Pathways through the Avebury Landscape; A study of spatial relationships associated with the Beckhampton Avenue, Avebury, Wilts.

Pathways through the Avebury Landscape – MSc dissertation

Pathways through the Avebury
Landscape

A study of spatial relationships associated with
the Beckhampton Avenue, Avebury, Wilts.

A dissertation submitted in partial fulfilment of the
requirements for MSc (Archaeological Computing) by
instructional course

September 2001.

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Table of contents.
INTRODUCTION; .................................................................................................................. 1
Historical background – Avebury Region. ...................................................................... 1
Theoretical Background – moving and experiencing; ..................................................... 4
Technological Background – GIS and three-dimensional reconstruction; ...................... 5
Geographic Information Systems; ............................................................................... 6
Three-dimensional Reconstructive technologies;........................................................ 6
Methodological background – analysing and visualizing;............................................... 8
AIMS AND OBJECTIVES ..................................................................................................... 12
General aims; ................................................................................................................. 12
Dynamic spatial relationships;....................................................................................... 13
Specific hypotheses; ...................................................................................................... 14
METHODOLOGY ................................................................................................................ 16
The three-dimensional reconstruction; .......................................................................... 16
The GIS;......................................................................................................................... 20
Linking the two;............................................................................................................. 22
Presentation of results;................................................................................................... 24
RESULTS ............................................................................................................................ 26
Results of the viewshed analyses;.................................................................................. 26
Results from the three-dimensional reconstruction; ...................................................... 28
DISCUSSION OF RESULTS .................................................................................................. 30
CRITIQUE OF THE METHODOLOGIES EMPLOYED ........................................................... 33
Implementing the GIS; .................................................................................................. 33
Constructing a three-dimensional reconstruction; ......................................................... 37
Using scripts to provide a dynamic link; ....................................................................... 38
Presentation of results;................................................................................................... 39
CONCLUSIONS ................................................................................................................... 40
BIBLIOGRAPHY ................................................................................................................. 43
Books, papers and journals; ........................................................................................... 43
World-wide-web references;.......................................................................................... 45
APPENDICES ...................................................................................................................... 47
Appendix I: Elevation model images............................................................................. 47
Appendix II: Cumulative viewsheds.............................................................................. 48
Appendix III: Frames from the Avenue viewshed animation........................................ 50
Appendix IV: Viewsheds calculated from locations around the study region............... 64
Appendix V: Rendered images from the three-dimensional reconstruction.................. 70
Appendix VI: Maps used in the project ......................................................................... 73

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Appendix VII: The “GoScript” Java program source code ........................................... 74
Appendix VIII: the VRML code designed to house GoScript....................................... 78
Appendix IX: the customised Avenue viewshed script ................................................. 78
ACKNOWLEDGEMENTS ..................................................................................................... 79

List of illustrations

FIGURE 1: PLAN OF LONGSTONES FIELD ................................................................................... 2
FIGURE 2: STUKELEY'S 1723 SKETCH OF THE WESTERN TERMINUS OF THE BECKHAMPTON
AVENUE ............................................................................................................................ 3
FIGURE 3: TENTATIVE INTERPRETATION OF THE STONE SETTINGS AT THE COVE (GILLINGS ET
AL. 2000)........................................................................................................................... 3

FIGURE 4; THREE-DIMENSIONAL RECONSTRUCTION OF ONE OF THE WEST KENNET AVENUE
STONES, FROM THE NEGOTIATING AVEBURY PROJECT ....................................................... 7

FIGURE 5; STUKELEY'S SKETCH OF THE BECKHAMPTON AVENUE, 1723 ................................ 15
FIGURE 6; SIMPLIFIED REPRESENTATION OF A RASTER DEM SHOWING POSITIVE AND
NEGATIVE LOS VECTORS ................................................................................................ 34

FIGURE 7; THE EFFECTS OF DEM RESOLUTION ON LOS VECTORS .......................................... 35
FIGURE 8: THE SAME SCENE VIEWED IN DIFFERENT BROWSERS TO SHOW INCONSISTENCIES
(GOODRICK, 1997) .......................................................................................................... 38
FIGURE 9: ELEVATION MAP OF THE 'FINAL STUDY REGION'.................................................... 47
FIGURE 10: CUMULATIVE VIEWSHED OF POINTS ALONG THE BECKHAMPTON AVENUE ......... 48
FIGURE 11: CUMULATIVE VIEWSHED, AS FIG.2, POST APPLICATION OF SMOOTHING ............. 49
FIGURE 12: AVENUE VIEWSHED ANIMATION - FRAME 1 ......................................................... 50
FIGURE 15: AVENUE VIEWSHED ANIMATION - FRAME 4 ........................................................ 51
FIGURE 21: AVENUE VIEWSHED ANIMATION - FRAME 10 ....................................................... 54

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FIGURE 34: AVENUE VIEWSHED ANIMATION - FRAME 23 ...................................................... 61
FIGURE 40: VIEWSHED CALCULATED FROM THE HYPOTHESISED WESTERN END OF THE
AVENUE .......................................................................................................................... 64
FIGURE 41: VIEWSHED CALCULATED FROM THE WESTERN HENGE ENTRANCE, THE EASTERN
END OF THE AVENUE ....................................................................................................... 65

FIGURE 42: VIEWSHED CALCULATED FROM THE COVE, LONGSTONES FIELD ........................ 66
FIGURE 43: VIEWSHED CALCULATED FROM LONGSTONES LONGBARROW............................. 67
FIGURE 44: VIEWSHED CALCULATED FROM SILBURY HILL .................................................... 68
FIGURE 45: VIEWSHED CALCULATED FROM THE SOUTHERN BANK OF WINDMILL HILL ........ 69
FIGURE 46: THE ENCLOSURE IN LONSGTONES FIELD .............................................................. 70
FIGURE 47: THE AVENUE AND COVE, LONGSTONES FIELD .................................................... 70
FIGURE 48: THE SECOND PHASE OF THE COVE, LONGSTONES FIELD ...................................... 71
FIGURE 49: THE HYPOTHESISED EXTENSION TO THE AVENUE BEYOND THE COVE,
LONGSTONES FIELD ........................................................................................................ 71
FIGURE 50: VIEW FROM ATOP SILBURY HILL LOOKING TOWARDS LONGSTONES LONG-
BARROW .......................................................................................................................... 72

FIGURE 51: VIEW FROM WINDMILL HILL TOWARDS LONGSTONES FIELD .............................. 72
FIGURE 52: HISTORIC OS MAPS OF THE AREA ......................................................................... 73
FIGURE 53: MODERN OS MAPS OF THE REGION ...................................................................... 73

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Introduction;

This project is an investigation into the spatial relationships associated with the
Beckhampton Avenue, Avebury, Wilts. through the Neolithic period; The study
region comprises the Beckhampton avenue and its environs. Notably, the study will
attempt to investigate dynamic spatial relationships, i.e. those associated with moving
around/through a landscape rather than from static viewpoints, as a means to shed
light on the position and development of the Beckhampton Avenue, which can be
seen as a formalised route, influencing movement. These relationships are to be
investigated by means of the concept of intervisibility using both the analytical
approach afforded by GIS techniques and a more subjective, reflexive approach
facilitated by an interactive three-dimensional model †.

Historical background – Avebury Region.

The Avebury complex comprises a substantial number of archaeological
monuments dating from the Early Neolithic through to the Early Bronze Age. The
earlier monuments comprised mainly long-barrows, including South Street and the
chambered tombs at West Kennet and East Kennet; there were also ditched enclosures
on Windmill Hill and in Longstones Field and the first phase of a henge at Avebury
itself as well as the first phase of activity at the Sanctuary on Overton Hill (see
Appendix I: Fig.9.). As the Neolithic progressed, the number of monuments increased
as the complex grew; apparent routes between monuments were formalised with stone
avenues, at West Kennet and Beckhampton, and older monuments were demolished,
replaced, added to or otherwise changed, as happened in Longstones Field and at the
henge itself. By the end of the Neolithic, a network of spatial relationships had been
defined by the monuments that had been placed within the landscape so that both
movement and vision were influenced.

† The term ‘three-dimensional reconstruction’ will be used in preference to any derivative of the
term ‘virtual-reality’ due to the problematic nature of the latter term (Gillings. 1997), especially in an
analytical context such as this project.

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Figure 1: Plan of Longstones Field

In Longstones field, a series of developments took place during the Neolithic. In
sight of both South Street and Longstones long barrows, the first phase of
development consisted of an oval, ditched enclosure with an entrance at one end,
roughly contemporary with the initial development at the henge itself. This enclosure
was relatively short-lived, with no evidence for re-cutting and only a thin turf line
having formed before the ditch was backfilled (Gillings, et. al. 2000. p13). This act of
backfilling may well have left a noticeable rise along the path of the ditches for some
time after the event (Wheatley, pers. comm.). Once the enclosure had been removed
from the landscape, at least in its original form, the initial phase of construction
involving megaliths began with a stone setting being erected at the Cove and the
Avenue; this initial setting was subsequently remodelled to form a rectilinear stone
setting, as shown in Fig.3. It is hypothesised that the avenue may have either ended at
the Cove or continued west towards the Beckhampton Road long barrow; Stukeley
hypothesised that the western terminus of the Avenue was near to the barrows at Fox
Culvert.

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Figure 2: Stukeley's 1723 sketch of the western terminus of the Beckhampton Avenue

The Beckhampton Avenue may well have continued beyond the Cove, as Stukeley
came to think, despite the lack of any recent evidence from excavation or field survey:
As well as Stukeley’s testimony, a sarsen burial pit was found on the projected line of
the Avenue by the modern day Calne Road (Gillings et al. 2000. 14).

Figure 3: tentative interpretation of the stone settings at the Cove (Gillings et al. 2000).

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Theoretical Background – moving and experiencing;

Movement is something humans do all the time and while we do we experience.
As Thomas argues: “The identification of locations as the ‘place of’ something
demonstrates the relational character of place. Human lives thread their way through
spaces and in the process our memories of having been are localised” (Thomas, 1996.
89). As such, movement plays a key role in forming society. It has recently been
argued that double-entrance henges are in some way associated with movement; i.e.
passage through the monument (Loveday, 1998. 17). Although Avebury is not a
double-entrance henge, the multiple entrances and the two avenues would suggest that
the concept of movement was involved in the design of the henge. If we assume,
therefore, that the avenues are associated with the movement of people through the
Avebury complex, we can start to investigate how this movement provides a
particular perception of the region. Loveday also noticed an association between the
alignments of double-entrance henges and much later route-ways where there can
have been no significant archaeological relationship between them; the inference
being that both the henge alignments and the later road alignments are related to
notions of thoroughfare (ibid.). Loveday also notes that the modern concept of a path
is not necessarily applicable to ancient route-ways (ibid. p24-5); rather than being
clearly defined, ancient routes were braided and very much interpretative, whereby
users were free to pick their way along a general path, guided by their surroundings.
Indeed, Ingold suggests that to primarily mobile populations (and there is scant
evidence for large-scale settlements from the study period in Wessex) the notion of
paths and places is more applicable than borders and territories (Ingold, 1980). In the
Early Neolithic Avebury region, the patterns of intervisibility associated with long
barrows suggests that each barrow was placed in a discreet visibility envelope
(Wheatley, 1996); as such, each barrow was revealed in turn as one passed through
the landscape. This suggests that the barrows were placed deliberately to be viewed
not from any one significant point, but as a sequence, revealed to the observer as
he/she moves through the area.

Barnatt (1998) argues that “Where people moved around the land, pathways
between places would be emphasised, and monuments sited beside them. Given the
scale of many Neolithic monuments, they may also have been placed at locales where
groups were in closer proximity at certain times of the year. At such times and places

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there was an increased propensity for both social tension and cooperation; monuments
may have been designed to both resolve and take advantage of these non-everyday
situations” (ibid. 93). In this way, the Avenues, can be seen to be the formalisation of
significant routes, routes which may have pre-dated the majority of the complex; the
other monuments can be seen to have located with respect to these routes, as Barnatt
advocates. Further to this, Thomas (1999. 202) argues that Windmill Hill causewayed
enclosure was a place used to control the transfer of people and things in and out of
the Wessex area from the Thames Valley to the north and further afield, suggesting
that the movement through the region may well have not been restricted to a small,
local population but perhaps to a much wider group of users.

Existing theory therefore suggests that through the Neolithic, we are dealing with
an experiential Avebury landscape, one in which there are special places and ways of
moving between and around them which are themselves being constantly
renegotiated; it is these ideas which are evident in the megalithic structures, other
monuments and relationships between monuments and/or their surroundings.
“Monuments played a fundamental role in the organisation of the prehistoric
landscape, helping to mark and characterise important places in the perceived scheme
of things. They were key elements in ‘sacred geographies’: Landscapes charged with
meaning” (Ruggles, 1998. 208).

Technological Background – GIS and three-dimensional
reconstruction;

Archaeologists often make use of scientific methods in order to test archaeological
hypotheses. Various forms of statistics are often employed and there is generally a
spatial attribute to archaeological data. For many years, this spatial element was
reduced to a representational tool, whereby aspects of the data could be visualized
arranged using the spatial attribute of the data. This resulted in methodologies
primarily based around the subjective interpretation of maps produced to demonstrate
particular aspects of a given dataset. On one level, applications of GIS and VR can be
seen to be a new way of representing spatial data in two and three dimensions
respectively; a continuation of the traditional way of dealing with spatial data. On
another level, three-dimensional reconstructions and GIS can be used as analytic tools
in order to devise and test hypotheses rather than simply basing hypotheses on a

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cursory visual inspection of the data: The ability to perform computationally
expensive tasks within an acceptable time span has made complex interrogation of the
spatial dataset, and calculation using the results possible.

Geographic Information Systems;

Geographic Information Systems are not a technology invented specifically for/by
archaeologists, rather they are another example of a set of tools borrowed from
another discipline. As well as being an excellent means of managing and presenting
spatial data, they include a range of analytical functions which can be informative to
archaeological investigations. It is now widely accepted that for representational or
data management purposes, in the field of cultural resource management for example,
GIS is extremely useful, but more analytic approaches, such as viewshed analyses
have received criticism for lacking any underpinning archaeological theory (e.g.
Aldenderfer, 1996). More recently, there has been a trend towards critical analyses of
the methodologies associated with using such procedures, and reflexive thought
regarding the input and output of the GIS (e.g. Fisher, 1991&1996; Gillings &
Goodrick, 1996).

This process has resulted in novel solutions to some of the criticisms levelled at the
analytic use of GIS. Of particular relevance to this project is the development of so-
called probabilistic or ‘fuzzy’ viewsheds (Fisher, 1992; Nackaerts et al. 1997),
whereby the resultant GIS output represents the probability of a particular cell falling
within the viewshed rather than a simple binary option. Issues such as this will be
dealt with in the critical evaluation section of this project.

Having said this, there are many examples of the use of GIS to inform
archaeological thought, and the continual process of developing and refining the tools
available within the GIS advances apace.

Three-dimensional Reconstructive technologies;

Again, three-dimensional modelling and visualization was not invented specifically
for/by archaeologists. The origins of three-dimensional modelling and visualization
techniques come from a range of sources including the disciplines of graphic design,
film-making, and architecture. Often used to reconstruct sites and monuments for
presentation to the public, as ubiquitously seen on Channel4’s ‘Time-Team’

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programme, three-dimensional reconstructions are often presented as an accurate
depiction of times past, with little discussion of how the reconstruction relates to the
evidence, the project aims or more abstract factors such as the budget or available
computational power. Such investigations often produce visually attractive results, but
whose archaeological integrity is perhaps questionable.

Three-dimensional reconstruction has also been used as an analytical tool to
investigate specific hypotheses. Recent work in this field has included Jennifer
Garofalini’s work on the Sanctuary, Overton Hill, Wilts., which allowed a number of
different hypotheses regarding the phases and development of the site to be
investigated. Another good example of this is the work by Wheatley, Gillings and
Goodrick on the Negotiating Avebury project, which includes a three-dimensional
reconstruction of the Henge and West Kennet Avenue. The model allows different
hypotheses regarding the position of the stones, the configuration of the entrance and
the alignment of the last section of the avenue to be investigated.

Figure 4; Three-dimensional
reconstruction of one of the
West Kennet Avenue stones,
from the Negotiating Avebury
project

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Methodological background – analysing and visualizing;

This project aims to use a combination of GIS and three-dimensional
reconstruction to elucidate the development of the Beckhampton Avenue. As such,
this project can be seen to be more closely related to analytical and theoretical uses of
such technologies rather than more representational based studies: Therefore, this
related studies section will focus on those studies which have had a direct bearing on
this investigation by using a combination of GIS or three-dimensional reconstructions
in an analytical way, particularly in conjunction with other supporting technologies,
rather than try to summarise the extensive corpus of work which makes use of GIS or
three-dimensional reconstructive techniques in general. Of particular note are the
range of studies which have attempted to use such technologies to investigate three-
dimensional spatial relationships in terms of visibility. Studies regarding the
phenomenological approach to the understanding of the development of
archaeological monuments are also relevant, as human perception and the subjectivity
of an observer must be taken into account.

The concept of visibility and intervisibility has been demonstrated to be a useful
concept for archaeologists ever since the first antiquarians travelled the country
drawing the vistas they saw. In recent years, the growth of computing has allowed
visibility studies to be performed using a range of computerised techniques, usually
adopted for the purpose. Studies which make use of the analytical qualities of GIS
systems include different types of visibility study: The ease with which computers can
calculate vast numbers of line-of-sight vectors greatly facilitates the formulation of
more advanced methodologies.

A good example of a viewshed based investigation which produced interesting
results was Wheatley’s (1996) investigation of the Early Neolithic Long Barrows of
the Avebury region. This investigation used viewsheds calculated from each barrow
in turn to show how each barrow was placed in its own distinct visibility envelope,
exposed in turn as the observer moved around the landscape.

A similar study of the Tall al-Umayri region, Jordan (Christopherson & Guertin,
1996), also used binary viewsheds calculated from points in the region to investigate
the intervisibility of the watchtowers present in the landscape. The investigation used
the observer height attribute of the viewshed calculation to represent the height of the

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walls and watchtowers, where the observer would most likely have been observing
from. This study demonstrated that although the visible area from the settlements
locations themselves were incredibly small, when each settlements network of
watchtowers was taken into account, each settlement showed a good level of control
over its respective territory, in terms of the area within the viewshed.

The calculation of viewsheds followed by their interpretation in terms of areas
visible is one of the most intuitive ways of using the GIS, but is by no means the only
way. The Tall al-Umayri investigation went further: The results from the preliminary
investigation were used to produce cumulative viewsheds over a long temporal range
for the study region. These viewsheds were used to test whether the number of
intervisible sites was statistically significant for each temporal zone compared to a
randomly generated set of sites and viewsheds.

While GIS based viewshed data can be interpreted both by visual inspection or
rigorous statistical association tests, it is often useful to further test the relationships
further; in the GIS this is not straightforward as the spatial dataset does not record
three-dimensional relationships, rather the system uses two-dimensions for recording
location with the elevation data being stored as another spatial attribute in the same
way as soil type or vegetation cover. Three-dimensional GIS is currently entering the
marketplace and is still firmly in development. This has resulted in the use of
supporting technologies which are capable of supporting corollary datasets or using
the same dataset in alternative ways, allowing the archaeologist to further test
potential relationships by whatever means.

An example of this is Gimblett et al.’s (1996) work on agent simulation, which has
attempted to use intelligent agents in three-dimensional simulated worlds derived
from GIS data to go further than would be possible using the GIS alone. The use of
intelligent agents dynamically interpreting GIS data, in order that the agents can make
decisions based on that data, has the potential to inform the archaeologist more than
evaluation of the GIS data alone.

Another good example of this is Bell’s (1998) study of the Whitby area where the
possibility of a Roman watchtower on a long eroded and disappeared section of coast
was confirmed using a combination of viewshed analyses and a CAD model of the
region. In this study, the model was used to approximate possible heights for the

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watchtower which could then be used as the observer height for further GIS viewshed
analysis. In Bell’s study, the model is not designed to reconstruct what was actually
there, but to augment the study by means of providing initial hypotheses to be tested
using the GIS: It is along these lines that this investigation of the Beckhampton
Avenue will progress, whereby the reconstruction will be used to test hypotheses
based on the results of the GIS analyses and vice-versa in a reflexive manner.

Methodologically speaking, this project can be seen to be strongly related to Earl’s
(1996) investigation of Danebury hill-fort. Earl’s methodology involved the creation
of landscape surfaces using the GRASS GIS and various modelling stages in
AutoCAD and 3D StudioMax. Unlike most reconstructions, where the modelled
structure is placed on an empty, flat plane, this methodology allows the effect of
topography to be taken into account, a factor which may prove highly significant in
the investigation of what is thought to be a formalised route-way, perhaps with far
more ancient origins.

If we now turn to some of the work relating to the perception of monuments,
particularly with respect to their visual appearance, there have a been a number of
important observations. One of the more important hypotheses with respect to this
project regards the use of colour, as described by Lynch (1998): This is critical to an
understanding of the patterns of visibility associated with the monuments that make
up the Avebury complex. The underlying bedrock is chalk, sometimes only a matter
of inches below the land-surface, and when cut into to form ditches, this white chalk
would have glowed in the light. The banks too, made up of the chalk rubble removed
from the ditches would have appeared brilliant. Factors such as these, that would
make some monuments more discernible at times of re-cutting or under different
lighting conditions, and certainly make them stand out from their surroundings,
cannot adequately be investigated using the GIS alone, but such factors can be
incorporated into the three-dimensional reconstruction for analysis. Indeed, Wood’s
(1998) paper which attempted to qualify some of the links between the analytical GIS
and the more subjective three-dimensional representation, considering factors such as
the mystery, drama, and satisfaction indices, measures of feeling or observer
experience.

Thomas’ (1999. 213-6) experiential account of moving along the West Kennet
Avenue and around the complex has also been useful in formulating ideas regarding

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how the complex may have developed. The Avebury Thomas describes is indeed an
experiential complex with many layers of meaning, some of which are associated with
the visibility relationships formed and broken as an observer moves around, and it is
against this background that this investigation of the Beckhampton Avenue will
proceed.

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Aims and objectives

The aim of this project, as already stated, is to investigate the spatial relationships
associated with the Beckhampton Avenue. Specifically, the aim is to investigate this
by means of a study of the patterns of intervisibility associated with the avenue and
associated monuments as one moves around the study region.

General aims;

The concept of movement is central to the aim of this investigation. It is possible
that the archaeologically significant relationships between monuments are not
necessarily direct, but involve a third party; the observer. In other words, while some
spatial relationships are fixed in the landscape, others are dynamically generated as
the observer moves around the landscape observing. Particular ways of moving
through the landscape will reveal a particular sequence of relationships: Some
monuments are nearly always visible, some only from within particular visibility
envelopes, and others seldom revealed. The aim is identify and investigate such
relationships in order to shed light on the development of the Beckhampton Avenue.

In order to do this, a combination of GIS and three-dimensional reconstruction was
chosen as being an ideal combination of investigative tools; the GIS can be used to
produce viewsheds for any given point in the study region while the three-
dimensional model can be used to investigate potential relationships highlighted by
the GIS. A dynamic link between the model and the GIS will provide a means of
producing three-dimensional views from within the GIS or calculating viewsheds
from within the reconstruction. It is anticipated that this link will facilitate the
reflexive nature of this investigation, whereby new ideas can be incorporated into the
system for analysis and the output from such analyses can be re-input and further
analysed.

As such, a secondary aim of the investigation is to critically evaluate the usefulness
of the chosen methodology in terms of the archaeological significance of the results
and the effectiveness of the system used. While it is believed that there is a sound
theoretical framework underpinning this investigation, the actual implementation will
be constrained by factors beyond control: The quality of the source data used,

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computer software/hardware limitations as well as time restrictions will all have a
bearing on the final project results. Indeed, the decisions made throughout the project
will also have been contributory to the results obtained. As such, it will be a
worthwhile exercise evaluating the ways in which such issues have impacted on the
project as a whole: As Hodder suggests, it is only through reflexivity and self-
criticism that research gains credibility in lieu of claims of objectivity (Hodder, 1999.
208).

The project aims are summarised below:

1. To investigate dynamic spatial relationships associated with moving
through the study region.

2. To construct a three-dimensional reconstruction and a GIS for the study
region, to facilitate 1.

3. To evaluate the effectiveness of the chosen methodology.

Dynamic spatial relationships;

One of the key aspects to this project is the idea of dynamic spatial relationships,
i.e. those which are constantly created and destroyed as an observer moves around a
landscape. There has already been much work using the notion of visibility defining
some of the static relationships between monuments in the Avebury complex (e.g.
Devereux, 1991 and Wheatley, 1996) which has demonstrated that some monuments
can be seen from others and that some monuments are placed in distinct visibility
envelopes. An aim of this project is to investigate the sequences in which
relationships between an observer and the monuments are formed, in terms of lines-
of-sight: This will be achieved by means of a dynamic link between a GIS and a
VRML model to allow movement through a virtual Avebury, where observations can
be made directly, while at the same time interrogating the spatial database, where
representations of the visibility envelopes, or viewsheds, can be output.

This dynamic link will be facilitated using the scripting facilities built into the
ArcView GIS, from ESRI. The aim is to provide an interface between the GIS and the
VRML world, which will involve passing data from the GIS to the VRML-enabled
web-browser, with the objective that potential sequences of relationships between the
observer and elements of the complex can be identified using the GIS and further

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investigated using the model before, if necessary, performing further analysis using
the GIS.

Specific hypotheses;

From an initial inspection of the model, a number of ideas emerged. In a similar
way to the arrangement of long barrows in the area, it would appear that the avenue is
positioned in such a way as to control what is visible to an observer travelling along
the avenue. Indeed, Thomas (1999. 214-6) has commented on the experiential nature
of the West Kennet Avenue and how the path the Avenue takes serves to control what
enters an observers visibility envelope and when. If the West Kennet Avenue is seen
as analogous to the Beckhampton Avenue, then it would seem logical to assume a
similarly controlled experience. As such, this investigation will focus on how the
viewshed changes along the Beckhampton Avenue in order to test the hypothesis that
this Avenue was carefully placed in relation to the surrounding topography and
existing monuments.

The Avenue may or may not have continued past the Cove in Longstones Field;
Stukeley certainly recorded it as far as the barrows at Fox Culvert, where he claimed
it terminated. If this was indeed the case, then it would be interesting to investigate
the associated patterns of visibility to test the hypothesis that this stretch of the
Avenue too was carefully placed with respect to the visibility of the other monuments
in the complex.

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Figure 5; Stukeley's sketch of the Beckhampton Avenue, 1723

The Cove in Longstones Field and the Beckhampton Avenue are assumed to be a
parts of a multi-phase monument (Gillings et al. 2000. 14-5), with the Cove marking
an original terminal to the Avenue. This would mean that Stukeley’s recorded stretch
is an addition: The three-dimensional reconstruction can be used to investigate
different phase arrangements in order to test this hypothesis.

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Methodology

As there are a number of distinct elements to this aspect of the project, each one
will be dealt with in turn.

The three-dimensional reconstruction;

The process of creating a three-dimensional reconstruction consisted of two
distinct modelling stages: The monuments themselves and the landscape on which
they are positioned. The process of modelling the various elements involved the use
of a number of different tools available in various software packages. AutoCAD R14
was used for the initial accurate modelling stages and georeferencing while later
assembly stages made use of the intuitive interface of 3D StudioMax. A number of
other utilities were used for various specific tasks along the way.

The barrows were modelled using AutoCAD, based on existing digitised base
plans, known measurements and accounts of the size and shape of the barrows. The
barrows were modelled using solid modelling techniques in order to facilitate later
stages of the methodology. The base plans, being georeferenced, enabled the model
elements to be constructed using real-world coordinates. The enclosures, on Windmill
Hill and in Longstones Field, were modelled using a similar range of techniques. The
measurements were once again based on existing excavation data.

The avenue and cove both involved a different set of techniques. The megaliths
were all based on generic rock-type surface models, freely available on the internet:
These models came in the form of three-dimensional triangulated wire-frames. These
rocks were deformed using the modifiers available in 3D StudioMax, which allow
fairly freeform, intuitive three-dimensional deformation, facilitating creating stones of
approximately the right shape and size. Having been satisfactorily modelled, the rocks
were exported as dxf files to be imported into AutoCAD where the individual rocks
could be placed in their appropriate georeferenced locations. A number of different
rocks had to created, as detailed in the table.

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Male Avenue stone Tall, thinner stones – approx 2-2.5m high
Female Avenue stone Squatter, squarer stones – similar height
Beacock stone Massive stones, analogous to obelisk at the henge (?) – approx
3-4m high
Adam (cove stone) Massive, rectangular slabs – based on the still standing Adam
stone
Eve (final avenue stone) Slightly larger avenue stone adjacent to cove – based on the still
standing Eve stone
Once the individual monuments had been modelled, each element was imported
into 3D StudioMax for the final assembly of the monumental complex. As each
element had been modelled using real-world coordinates, the x and y spatial attributes
of the complex as modelled was correct, although at this stage, the z (elevation)
attribute was limited to being correct within the individual elements only. The next
stage, construction of the landscape surfaces, would alleviate this problem by
providing elevation data for the model.

Creating three-dimensional landscapes has been crucial in the disciplines of
computer generated art and computer gaming although the focus of development has
been the generation of aesthetically pleasing landscapes rather than being an accurate
representation of a given spatial dataset. As such, many of the tools available for
creating landscapes in commercially available software packages are not suitable for
creating accurate representations of DEMs: There are becoming increasingly available
dedicated landscape modelling packages capable of importing a variety of commonly
available GIS software formats although these are currently very expensive,
commercially available packages, not suited to such a project as this. The
methodology adopted is reflective of the software available and the need for a
justifiable level of accuracy over purely aesthetic values.

The landscape surfaces needed to be of an acceptable level of accuracy in order
that the model is representative of the real-world situation, essential if the model is to
be used to test hypotheses based on the concept of visibility. There are, however,
problems with this approach. Firstly, a high level of detail (LOD) requires a high
number of surface nodes. Secondly, there are constraints on the number of surface
nodes which can be used within a given surface, both those defined as part of the
VRML standard and also those imposed by available computational power. These two
considerations must be considered together with the resultant surface being an
acceptable compromise between the two. A good way of representing surfaces with
an acceptable LOD whilst reducing the number of nodes is as a Triangular Irregular

17


Network (TIN) rather than an Elevation Grid: Unlike the Elevation Grid, the TIN does
not have a fixed sample rate allow more nodes to be used to represent areas of the
surface with the greatest amount of change. The process of creating and
georeferencing such land-surfaces involves a number of different steps, outlined
below:

Step1: Export DEM from GRASS as ASCII raster
Step2: Produce VRML Elevation Grid from DEM using LandSerf
Step3: Clean/validate VRML using Chisel
Split Elevation Grid into compound Elevation Grid using Chisel
Step4: Import VRML into 3d StudioMax
Apply ‘simplify grid’ modifier to each of the grid objects
Step5: Export all of the grid objects as a dxf file, with all objects on one layer
Step6: Import into AutoCAD
Scale and position grids to real-world coordinates
Adjust base elevation of grids to real-world elevation

The original dataset consisted of digitised 1:50,000 contour data for a 20km square
around Avebury. It would be impossible to use the whole of this dataset for the
construction of a model due to the sheer scale; instead, it was decided to create a
surface based on a smaller region, a subset of the data, but on which all of the
monuments being modelled could be placed. Initially, it was intended to interpolate
the contour data at a five meter resolution although it soon became apparent that the
area which could be modelled at this resolution would be too small and there would
be questions relating to the validity of such an interpolation, given the resolution of
the original dataset. Given the need for a large enough study region, and the resolution
of the original data, it was decided to interpolate a larger DEM at a resolution of ten
meters. The regions defined in the GRASS GIS are detailed in the following table:

Region Name Lower-Left corner Upper-Right corner Interpolated No.
DEM resolution cells
FinalStudyRegion 407000,168000 411000,172000 10m 400x400

MiddleBit 408475,168775 410625,170425 5m 430x330

Having defined suitable regions, DEMs of each were produced. This was
accomplished by sampling the vector data at the required resolution using the v.to.rast
command; the resultant file was then used as the input for the r.surf.contour
command, which uses an algorithm to interpolate elevation values for each pixel in
the resultant raster output file. The resultant DEMs were then output as ASCII text
files using the r.out.ascii command ready for the next step of the methodology.

18


The next step was to create surfaces based on the DEMs output from GRASS. This
was achieved using the LandSerf GIS package which has the ability to import GRASS
ASCII raster files and export VRML elevation grids. There is native support within
GRASS for producing VRML format output using the v.out.vrml command but,
unfortunately, this was not available at the time of this project. The resultant elevation
grids, in their original state, contained vast amounts of redundant elevation data;
indeed, given that LandSerf exports one elevation grid square for each cell in the
original DEM, the number of nodes far exceeded the maximum permissible number
of 16000. This led to the need to further process the elevation grid files in order to
make them useable. For this, a package called Chisel was used which includes a suite
of tools for optimising, cleaning and validating VRML files. Each Elevation Grid was
split into a number of smaller spatially referenced grids, which when displayed
together appear indistinguishable from the original grid, but each one with fewer than
the maximum permissible number of nodes: This operation resulted in a considerable
reduction in file size and removed all VRML non-complicity errors.

The final stage of producing the surfaces was to simplify the Elevation Grids in order
to reduce the amount of redundant data. This was achieved using the simplify grid
modifier in 3d StudioMax applied to each of the sub-grid objects, which uses a
triangulation algorithm to optimise the surfaces and reduce the number of nodes and
faces contained within a surface. This process is often referred to as ‘decimation.’
Once complete, the files were saved as dxf files for import into AutoCAD where the
surfaces were positioned and scaled to real-world coordinates.

Once the land-surfaces and monuments were complete, the AutoCAD files were
imported directly into 3D StudioMax for the final assembly stages. As the AutoCAD
files made use of real-world coordinates, at least in the x-y plane, each element was
automatically placed in the appropriate position upon import. The elevation of the
megaliths in relation to the land-surface was corrected by moving each element
manually parallel to the z-axis until it looked to be in the appropriate place in the
perspective view. The other monuments (the enclosures, henge and Silbury Hill) were
attached to the land-surface by means of a conform Space Warp. This was applied to
the base vertices of each monument and works by forcing these vertices to obtain their
z-coordinate from a user specified plane, in this case the land-surface.

19


Having corrected the relative elevations within the model, it was necessary to correct
the absolute elevation of the model as a whole in order that the three-dimensional
coordinates of any point within the model is representative of the real-world situation.
This was accomplished by moving the entire model parallel to the z-axis to the
appropriate position, based on known coordinates/elevations provided by the GIS.

Finally, textures and lighting were applied to the model before final rendering of still
images and animations. Colour bitmaps were used to provide textures for the stones
and the grass, while the same bitmaps were used as bump-maps to provide the illusion
of three-dimensional surface texture. The lighting was accomplished by means of a
sunlight system, allowing fairly realistic light to be added. The still images and
animations were rendered using a variety of resolutions and levels of detail: Generally
a small version of each animation was created, for potential web-based dissemination.

The model was then exported as a VRML world to be linked to the GIS. Additional
scripts were added manually to provide a means of controlling the phases of the Cove
and enclosure in Longstones Field.

The GIS;

The GIS part of this project involved the use of the GRASS GIS to produce the
DEMs used in the subsequent analysis, performed using ArcView. The decision was
made to implement the analytical part of the project using the ArcView GIS rather
than the GRASS GIS due to the internal structure and workings of the system:
ArcView runs on the Windows platform and is based around the Avenue scripting
language, an object-oriented language similar to Java, compared to GRASS, which
runs primarily on Unix platforms and is based around the C procedural programming
language. The use of the Windows based, object-oriented system greatly facilitated
the aim of providing a dynamic link between the GIS and the VR model.

The ArcView GIS was set up using the same data as was used for the VR model:
The interpolated DEMs output from the GRASS GIS. The ASCII raster files output
from GRASS are of a slightly different format to those accepted by ArcView. As
such, it was necessary to first modify the file-headers using a text editor to make the
files compliant with the ArcView ASCII raster file format. The differences in the file
headers is illustrated in the table below:

20


GRASS ASCII raster header ArcView ASCII raster header
north: value Most northerly coordinate nrows: value Number of rows
south: value Most southerly coordinate ncols: value Number of columns
east: value Most easterly coordinate xllcorner: value x-coordinate, lower-left corner
west: value Most westerly coordinate yllcorner: value y-coordinate, lower-left corner
rows: value Number of rows cellsize: value grid resolution
cols: value Number of columns

Once made compliant, the ASCII raster files were imported into ArcView. Both of
the interpolated DEMs based on the original GRASS regions were imported as well as
an interpolated DEM representative of the whole area covered by the original dataset.

Features were added to the GIS by means of the CAD-reader extension, facilitating
the inclusion of AutoCAD files generated from the original two-dimensional files.
Two such files were included, one containing the prehistoric features in the region,
bounded by the World Heritage Site boundary, the other containing modern features
to facilitate understanding and interpreting the area. A third AutoCAD file was also
included which contained a line representing a theorised path along which the
Beckhampton Avenue may have continued past Longstones Field.

Binary viewsheds were calculated using a customized version of the SA: Visibility
script which is part of the ArcView vistools extension (vistools.avx) written by Esri
and available on their website. This script calculates a binary viewshed based on user
defined observer and target locations, observer and target offsets and a field of view.
For the purposes of this investigation, the offsets were both set to two metres and the
field of view was set to three-hundred-and-sixty degrees to provide a complete
viewshed.

In addition to this, cumulative viewsheds were prepared for the points along the
theorised path of the Beckhampton Avenue. This was accomplished using the
Spatial.SimpleVisibility script, the input being a digitised line in a shapefile theme
following the theorised path. The cellObserved flag was set to false in order that the
resultant product represented the frequency of each cell being observed from the
observer locations. The resultant map had a frequency range of 0-25, representing the
twenty-five observer locations (nodes) along the line.

Viewsheds calculated from points along the Avenue were then labelled and
assembled into a short animation using Macromedia Fireworks in order to illustrate
how the viewshed changes as the observer moves along the Avenue.

21


Linking the two;

The process of linking the two components of the system together involved a
number of stages. The first stage involved creating a viewshed using the GIS, the
second stage involved converting and passing data describing the view to the VRML
browser, and the final stage involved rendering the view in the browser.

Calculating viewsheds is one of the scripts available in the vistools package,
available from ESRI. For this project, the SA: Visibility script was modified to include
extra code which would save necessary data to a user specified file: This data
consisted of the x,y coordinates and elevations for the observer and target locations.
Views in the world of VRML are defined in a slightly different way: rather than being
defined by two locations representing an observer and a target, the view is described
by the following attributes:

• Position – a three dimensional vector describing translation from the
origin.

• Orientation – a three-dimensional unit vector representing the axis of
rotation plus an angle of rotation.

• Field-of-view – the preferred minimum viewing angle, in the range 0-pi.

According to the VRML97 ISO specifications, Java and JavaScript are the
recommended means of interfacing with VRML worlds. The process of modelling
responsive, dynamic events in VRML makes use of the ‘event’ concept whereby any
action within the VRML world triggers an event: these events are then routed between
‘nodes’, the building blocks of the world. A simple example of this would be a set of
traffic lights, where the light nodes would have events routed to them from a
timeSensor node, causing the lights to turn on and off in sequence according to the
events generated by the timeSensor. For this project, a slightly more complex
arrangement is required as the event which changes the position and orientation of the
observer needs to obtain values from a file output from the GIS: This is achieved by
means of a script node, which is able to change values of exposed fields within parent
nodes according to some external input. In this case, the parent node is the viewpoint
node and the exposed fields which need to be altered are position and orientation.

22


For simple scripts, it is possible to use JavaScript embedded directly within the
VRML file, but the functionality of JavaScript is limited, especially in the area of file
input/output: JavaScript does not have the capability to write to files due to the
inherent security risks associated with this in most situations in which JavaScript is
deployed. This combined with the need to process the incoming data before passing it
to the vrml-browser made JavaScript unsuitable for the task in hand: As such, a full-
blown Java program implementation was used instead.

The Java program had to provide three main functions. Firstly, the program had to
read input from the file output from the GIS; secondly, the data had to be processed;
finally, the exposed fields in the parent node had to be set to the new values. The
calculation part of the process is based on Loren Siebert’s “VRML Camera
Calculator”, a JavaScript application based on Stephen Chenney’s C code. This led to
the creation of two initial classes of object. Firstly, the CameraCalc class, based on
Loren Siebert’s work, which had methods for performing the calculations necessary,
with additional methods for choosing an input file, and reading from the input file.
Secondly, the GoScript class, which has methods for being initialised and processing
events, according to the VRML97 specification: It is this class which is instantiated
by the script node and then subsequently instantiates the CameraCalc class as part of
the processEvent() method. There are also subsidiary classes of objects needed by the
CameraCalc class: These are the Vector class, the Quaternion class and the Orient
class.

23


As a contingency measure, the observer and target locations were converted to
VRML viewpoints manually using Loren Siebert’s ‘VRML camera converter’; this
was achieved by simply using the camera converter from within the web-page from
whence it originally came. The z-value had 2m added each time to allow for the
observer/target offsets. The results of this are summarised in the table below:

Avenue script Obs. Target Orientation (x,y,z) Theta (radians) Focal
output location location Distance
filename (x,y,z) (x,y,z) (m)
Silbury 2 409996, 407545, 0.040881639172605365, 1.562795088595225 2459
avend 168530, 168733, 0.9983441463351585,
187 163.166 0.04046797569541446
Avend 2 407552, 408666, 0.4806582348425075, 1.9071559325418645 2946
windmill 168735, 171463, -0.7200793338820061,
165.044 196 -0.5004532087959187
Avstart 2 410060, 407547, -0.21286764278843428, 1.6207478516012154 2775
avend 169913, 168735, 0.9534568797707983,
158 165.012 -0.2135587625723392
Cove 2 silbury 408898, 410007, -0.2825422250920499, 1.6697325198648671 1337
169303, 168555, -0.9150970922977689,
166 182.145 0.2876928965202337
Longstoneslb 408701, 408672, 0.25825318067922, 2.6274083165759205 2316
2 windmill 169147, 171463, 0.6703017339068092,
163.498 196 0.6957017178292658
Southstreet 2 409027, 410063, 0.2611585885319172, 1.6367790838244908 1215
avstart 169276, 169912, -0.9300930677282172,
166.893 158 -0.25830810478947485
Windmill 2 408749, 410239, -0.3338701813329973, 1.6785795741329381 1996
henge 171305, 169977, -0.8853477062082908,
195.636 163 0.3235585590405373

In the table, the location avend is the hypothesised end of the Avenue, at Fox
Culvert while avstart is the other end of the Avenue at the Henge: This does not imply
a direction of movement along the Avenue, rather the terms are simply a means of
differentiating between each end of the Avenue.

Presentation of results;

The presentation of results will involve a number of different formats. There will
be a printed, bound write-up of the project, according to University regulations, but
there will also be a multimedia element incorporating as much of the data used in the
project as possible. This multimedia element will be based around a series of HTML
pages and will include animations rendered from the model to illustrate particular
routes as well as high-resolution still images of particular views. The CAD files and

24


other files associated with the construction of the model will also be included. The
aim is to provide the reader with as much of the data used in the investigation as
possible, to allow them to replicate parts of the project or try out their own ideas:
Ideally, the whole model/GIS system would be mounted on CD for distribution
alongside the traditional bound version.

The output files from both the GIS and the reconstruction, in the form of images
and animations, are included in a series of HTML pages on the CD, allowing the user
to browse the images easily and have a reference. The VRML world is also linked to
these pages, as are links to install suitable browsers (two of which, Cortona and
CosmoPlayer are included on the CD). Finally, the 3D StudioMax files are also
included as an archive, as is the GIS. The GIS data is included as a self-extracting
archive that will install the GIS to the appropriate directory and add shortcuts to it
(Windows platforms only).

25


Results

Results of the viewshed analyses;

Starting with the cumulative viewshed analysis (see Appendix II; Figs. 10-11),
calculated using points along the path of the Beckhampton Avenue, it is clear that
certain parts of the landscape consistently fall within viewsheds (indicated by areas of
higher frequency represented by darker shades of red). These include the western side
of Waden Hill, notable for its lack of prehistoric archaeology, and Silbury Hill both of
which have very high frequency responses. Other places, such as Longstones and
South Street long-barrows and Windmill Hill’s southernmost outer bank and ditch
circuit fall within, have mid-frequency responses indicating that they fall within a
significant number of viewsheds. An interesting observation is that the enclosure in
Longstones Field sits in an area of low frequency, surrounded by an area of higher
frequency suggesting that it can be seen from fewer locations along the Avenue than
its immediate surroundings.

If we know turn to individual viewsheds calculated along the path of the avenue,
the patterns of visibility highlighted by the cumulative viewshed analysis can be
investigated in more detail (See Appendix III: Figs 12-39). As the observer moves
along the avenue, it is possible to note the changing viewshed. In particular, there are
a number of distinct phases to the changing viewshed, as detailed in the table below:

26


Phase Frames Description
A 1-5 Visibility is restricted to the section of the Avenue nearer to the Henge and to
the high ground: Silbury Hill is prominent throughout, as is Waden Hill. The
middle section of the Avenue is obscured including the site of Longstones
enclosure and the South Street and Longstones long-barrows.
B 6-14 Visibility becomes restricted to the mid-section of the avenue, with the section
nearer to the Henge gradually disappearing from view from frame 7. Silbury
Hill also becomes obscured from frame 8. The end section of the Avenue
beyond Longstones long-barrow is also outside of the calculated viewshed.
Longstones long-barrow is tentatively close to the edge of the viewshed and
may well come into view at some time during this phase; certainly is would be
visible by frame 14.
C 15-20 The section of the Avenue between the Henge and Longstones Enclosure
gradually disappears from sight while at the same time, the area of the valley
floor to the south enters the viewshed and everything to the north, apart from
the summit of Windmill Hill is obscured: By frame 18, Windmill Hill has also
become obscured. Waden Hill also disappears from sight during this phase
while Silbury Hill reappears when the observer reaches Longstones long-
barrow (frame 18). The end section of the Avenue towards Fox Culvert is still
obscured by the slight prominence over which the Avenue rises.
D 21-23 The end of the Avenue is finally revealed at Fox Culvert with South Street and
Longstones long-barrows and Longstones enclosure still falling within the
viewshed. The whole top of Waden Hill also becomes visible again as does the
Henge as the observer rises up onto higher ground, although the Avenue
between the henge and Longstones enclosure is obscured.
E 24-28 The monuments in and around Longstones Field disappear from the viewshed,
as does the Henge and the majority of the Avenue, while at the same time the
whole of the section of the Avenue towards Fox Culvert is exposed. Silbury
Hill and Waden Hill both remain prominent.

In other words, as an observer moves along the path of the avenue, monuments
enter and leave the visibility envelope in sequence. The avenue is revealed a section at
a time and at no point is it possible to see the Avenue as a whole; rather it is revealed
as the observer moves along and around the Avenue.

Taking the viewsheds calculated from neighbouring locations into account (see
Appendix IV: Figs 40-45), it becomes clear that there are patterns of intervisibility
between the Avenue and the other monuments within the monumental complex. The
viewsheds are summarised in the table below.

27


Observer location Description of viewshed
Western Henge Silbury Hill, South Street long-barrow and the initial stretch of the
entrance, end of the Beckhampton Avenue are within the viewshed as are the northern slopes of
Avenue: Fig.41. Waden Hill and the southern slopes of Windmill Hill, including the
causewayed enclosure. The other end of the Avenue may have passed
through the viewshed: The hypothesised path runs tentatively close.
The Cove, The viewshed calculated from this location encompasses many of the
Longstones Field: monuments of the study region: Both Longstones and South Street long-
Fig.42. barrows, Windmill Hill and Beckhampton enclosures, the Henge itself and
the middle section of the Avenue. Waden Hill is also within the viewshed
but Silbury Hill and both ends of the Beckhampton Avenue are
conspicuously excluded.
Longstones long- Only a small section of the Avenue is within the viewshed, although the
barrow: Fig.43. Cove and enclosure in Longstones Field, South Street long-barrow,
Windmill Hill enclosure and Silbury Hill are included. Waden Hill and the
Henge are excluded.
Silbury Hill: This viewshed is fairly all-encompassing: The only monuments not within
Fig.44. the viewshed are those in Longstones Field (the Cove, enclosure and South
Street long-barrow and a short middle section of the Avenue).
Windmill Hill, All the monuments in the study region are within the viewshed, although
southern-most the Avenue is only included as far as Longstones long-barrow.
bank: Fig.45.

Results from the three-dimensional reconstruction;

The results from this part of the analysis are presented as series of rendered images
(see Appendix V: Figs.46-51) and animations, which can be found on the
accompanying CD. In addition there is a vrml world, originally intended to be linked
to the GIS, also found on the accompanying CD. The results support those found
using the viewshed analyses but by incorporating perspective, provide more
information regarding the view: It is interesting to note how quite large megaliths
disappear into their surroundings and are unperceivable in the rendered images
although the calculated viewshed would suggest that a line-of sight relationship exists.

If we look at the development of the monuments in Longstones Field, a number of
observations can be made. Firstly, the way in which the later Avenue respects the
earlier enclosure is quite clear (Fig. 46-7) with the Avenue running through what
would have been the entrance to the enclosure. Secondly, the way in which the initial
Cove layout was centred on the line of the Avenue is apparent, but the transition from
phase one to phase two of the Cove is interesting as the box-like arrangement is
noticeably off the centre-line of the Avenue, centred on the northern line of megaliths
instead. Indeed, there appears to be a slight shift in alignment between phases one and
two of the Cove as well, bringing the more open side of the cove in phase two, to the

28


south-east, round to be more in alignment with Silbury Hill: This is quite noticeable
from an elevated view which allows the observer to look over the intervening terrain.

Another observation is the way in which the western end of the Beckhampton
Avenue is not visible from Windmill Hill. First highlighted using the GIS, the
reconstruction confirms the way in which the Avenue moves behind a prominence
past Longstones long-barrow.

29


Discussion of results

The GIS highlighted some interesting patterns with respect to the changing
patterns of visibility associated with moving along the Beckhampton Avenue. These
were supported by the views from the three-dimensional reconstruction. As first
thought, the Avenue is positioned in such a way a to guide movement and visibility
without being restrictive. The way in which monuments enter and leave the viewsheds
calculated from points along the Avenue suggests that the Avenue may well have
been deliberately positioned to take advantage of the topography in guiding the
observers gaze. As with the southern Henge entrance at Avebury, the course of the
Avenue follows the terrain in such a way as to provide a succession of false horizons
to the observer, with monuments along the path of the Avenue exposed in sequence.

Walking from the hypothesised Fox Culvert end of the Avenue, the observer walks
over a rise and is presented with a view of the Longstones and South Street long-
barrows, the Cove and, in the distance, perhaps a brief glimpse of the Henge, although
the Avenue itself disappears again beyond the area once occupied by the
Beckhampton Enclosure. All this time, Silbury Hill rises above the horizon over on
the right. As the observer passes Longstones long-barrow, Silbury Hill becomes
obscured and more and more of Windmill Hill, with its banks and ditches, rises above
the near horizon. The end of the Avenue from whence the observer came has now
dropped out of sight and gradually the Avenue towards the Henge is revealed as the
observer continues. Having reached the area once occupied by the Beckhampton
Enclosure, the Henge gradually comes into view and on the final approach to the
Henge, the monuments in Longstones Field drop behind the near horizon. In other
words, as an observer moves through the landscape, the position of the monuments
relative to each other, the landscape and the observer, and the relationships that are
constantly formed and broken serve to produce a narrative, an experiential journey.

As regards the hypothesised section of the Avenue between the Cove in
Longstones Field and Fox Culvert, both the GIS and three-dimensional reconstruction
suggest that this section of the Avenue would also have followed the pattern exhibited
by the known section of Avenue. As with the West Kennet Avenue, the end furthest
away from the Henge curves around a prominence, resulting in a view dominated by

30


near horizons and the high ground to the south of the study region. Indeed, it is only
from this hypothesised extension to the Avenue that Silbury Hill once more comes
into view, having been obscured for much of the known path of the Avenue: Again,
this could be analogous to the West Kennet Avenue where Waden Hill obscures the
view of Silbury Hill apart from at the Henge and towards the Sanctuary.

The three-dimensional reconstruction of the cove provided a useful means of
investigating its potential development. Using the hypothesised phases for the Cove as
defined by Gillings et al (2000) and the reconstruction (see Appendix VI: Figs.46-50),
it was possible to identify the following stages in the development of the monuments
around Longstones Field:

Stage Description
I Before the construction of the Avenue, the enclosure was constructed near to South
Street and Longstones long-barrows, with an entrance to the north-east towards the
Henge. The area chosen for the enclosure was situated so as to only be seen from
certain places in the landscape.
II The enclosure was backfilled and the Avenue constructed as far as the Cove,
respecting the alignment of the enclosure entrance. Phase 1 of the Cove probably
constructed during this stage.
III Phase 2 of the Cove constructed, probably shortly after Stage II.
IV Avenue continuation added, heading past Longstones long-barrow, over a slight rise
and out of view.
While this is a probable sequence of development for the monuments in
Longstones Field, in reality the final three stages may well have been almost
consecutive or even contemporaneous. The apparent shifting in the Cove’s alignment
between stages II and III in order to bring it more into alignment with Silbury Hill is
an interesting observation. Although Silbury Hill cannot be seen due to the
intervening rise, and the shift in alignment is slight, it may be an archaeologically
significant observation, perhaps related to the broader patterns of visibility associated
with the full hypothesised length of the Avenue and Silbury Hill: While Silbury Hill is
visible from either end of the Avenue, it is obscured for the middle stretch through
Longstones Field where the Cove appears to be have repositioned to face it. Indeed,
the box-like arrangement open out along this alignment.

A number of issues have to be considered when interpreting the viewsheds
calculated using ArcView. Firstly, the calculation of a binary viewshed is not
necessarily the most satisfactory means of investigating visibility patterns, but given
the scope of this project and time available, it is a useful tool: As the aim was to
investigate the dynamics of the situation, how the viewshed changes, without making

31


assertions based on spatial statistics, it was felt justifiable. This will be dealt with in
full in the critique of the methodology. The binary viewsheds show quite well, when
viewed in sequence, the way in which patterns of visibility change as an observer
moves along. Secondly, they do not take into account issues such as perceivability or
vegetation cover, both of which would have had a significant influence on what an
observer would be able to see.

If we first take the evidence for the vegetation cover in the region, there is
evidence for a significant amount of clearance by the time of the mid-third
millennium BC (Malone, 1989. 34). Indeed, assuming a relatively late date for the
formalisation in stone of the Avenue, it would have been placed in countryside that
would have been cleared previously and then subsequently regenerated to a level of
scrub (ibid. 14-5). Whittle argues that by the mid-third millennium BC, there was a
phase of renewed clearance, after the regeneration mentioned by Malone (Whittle,
1993.35). If the scope of the projects had allowed, it would have been worthwhile
investigating hypotheses regarding vegetation cover in the region and how this affects
visibility based studies, particularly how vegetation may have affected the specific
observations herein noted.

The results from the three-dimensional reconstruction augmented the results of the
GIS and provided a means of testing the issue of perception. Despite the scale of the
Avenue, the stones themselves can easily blend into their surroundings when viewed
from a distance, especially if the lighting conditions are less than perfect or there is a
little fog; see the rendered images on the accompanying CD. The banks, with their
chalky texture, proved to be highly visible, as first thought. To thoroughly investigate
how the appearance of the monuments in their environmental context affected their
visibility and their visual impact, it would have been necessary to more rigorously test
different materials and environmental conditions using the three-dimensional
reconstruction; despite this, the results from the analysis were interesting and the
resultant images did serve to illustrate the effect of selected conditions on visibility.

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Critique of the methodologies employed

The various stages of the methodology were at times rather complex, involving
many operations and a range of software. “The equivocality, heterogeneity or
multiplicity of the material world means that choices must be made in perception and
to what we attend” (Shanks & Hodder, 1995. 11). Each section will be taken in turn,
the methods and decisions made analysed and discussed in terms of their effectiveness
and how improvements could possibly be made in future. In particular, the way in
which the underpinning theoretical framework supports the use of the GIS will be
discussed, especially how the technology itself has impacted on the investigation
(Rivett, 1997. 15).

Implementing the GIS;

Implementing the GIS itself was unproblematic and performing the viewshed
calculations was not that complicated (Kvamme, 1993. 77), although a number of
caveats need to be examined. Firstly, there needs to be a discussion of the nature of
DEMs and how they affect subsequent analyses, particularly visibility based studies.
Fisher (1991. 1321) has noted how the DEM can often be the prime determinant
factor in viewshed analyses, due to the way in which line-of-sight calculations are
performed by the GIS, and due to error inherent in the DEM.

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Figure 6; Simplified representation of a raster DEM showing positive and negative LOS vectors

The script used in ArcView performs viewshed calculations on elevation grids,
raster representations of the landscape with a fixed resolution. As such, the landscape
can be seen as being represented by an array of blocks of equal area and varying
heights (see Fig.6&7). This method of representing landscape surfaces tends to be
most effective at representing surfaces with little change in elevation: The lower the
resolution, the more rounding of elevation values occurs, producing a land-surface
with less detail. In Fig.7, the same landscape surface is represented by increasingly
higher resolution raster DEMs and it is clear how the resolution of the schematic
Deleted:
DEM affects lines-of-sight. Also of importance is the interpolation algorithm used to
interpolate the DEM from the original contour data. It is worth noting that the
algorithm implemented in the r.surf.contour GRASS command is known to have
problems when the distance between known values exceeds a certain limit: Due to the
use of 10m contour data, over what is effectively a region with a relatively small
elevation range, this problem became evident. Indeed, r.surf.contour uses a flood-fill
type algorithm rather than a more complex inverse distance weighting interpolation
algorithm, as found in other commands such as r.surf.idw: The use of such an
algorithm would have reduced the noticeable stepping effect in the DEM. Indeed, the

34


secondary products calculated from the interpolated DEM, particularly the slope map,
clearly showed the stepped nature of the DEM caused by the use of the r.surf.contour
interpolation algorithm.

Figure 7; the effects of DEM resolution on LOS vectors

In the case of this investigation, a resolution of 10m was chosen for the
interpolated DEM as the original contour data was at 10m intervals: Any higher
resolution would be most likely to represent the nature of the interpolation algorithm
rather than the actual landscape surface. As can be seen from Fig.7, if the resolution
of the DEM is not sufficient, the DEM can have adverse effects on subsequent
analyses.

Given the problems outlined above, there has to be a level of uncertainty regarding
the resultant output: The binary viewshed suggests that there are only two possible
options regarding the visibility of a given cell in the analysis which, given the
problems associated with DEM interpolation, represents a considerable simplification
of the situation. While it would have been preferable to use a technique which would
be able to take into account the error factor inherent in the DEM, such as the Monte-

35


Carlo methodology advocated by Nackaerts et al. (1997), the binary viewsheds
calculated as part of this project were indeed informative; the use of probabilistic
viewsheds should undoubtedly be considered for any future study.

As such there are two important observations to be noted: Firstly, the interpolation
stage used to produce the DEM is critical for subsequent analyses. Secondly, the
resolution of the DEM is critical for viewshed analyses. These problems have to be
accepted due to the strict time constraints set for the project, but for future
investigations the following steps would greatly improve the methodology:

• Original data – 10m interval contour data is not sufficiently detailed to create
accurate DEMs using the r.surf.contour command: It would be better to
use at least 5m contour data, obtainable from the Ordnance Survey.
Alternatively, a more sophisticated interpolation method should be used.

• Viewshed calculation – raster based elevation grids can prove unreliable for the
calculation of viewsheds, as described above. An alternative would be to
use a TIN-based system, as used for the three-dimensional reconstruction.
Unfortunately, the Avenue scripts contained in the spatial analyst
extension for ArcView calculate viewsheds using the elevation grid
approach, and it was necessary to modify existing scripts rather than write
new ones due to time constraints.

• Advanced viewshed calculation – rather than simply calculating binary
viewsheds, a better approach would be to use probabilistic or ‘fuzzy’
viewsheds. In a probabilistic viewshed, at least a hundred viewsheds are
calculated, each using a different degree of random noise applied to the
DEM within user-defined parameters: The resultant viewshed represents a
percentage chance of a given point being within the viewshed rather than a
simple in/out binary value.

These criticisms do not mean that the binary viewsheds calculated as part of this
project are meaningless; rather, the incorporation of the recommendations listed
above would have facilitated more detailed, statistical analyses of the results,
including tests to measure statistically the degree of association between the
monuments and the viewsheds. As such, the viewshed analyses conducted as part of

36


this project have been useful in identifying changing patterns of visibility within the
study region.

Constructing a three-dimensional reconstruction;

The construction of an accurate three-dimensional reconstruction proved to be less
straightforward than first imagined. The range of software needed to perform each
step of process resulted in a cumbersome methodology. Unfortunately, there was no
easy way to simplify the process: Each step provided a specific means to an end and
was essential for subsequent steps.

The production of realistic land-surfaces was quite effective, despite the number of
stages involved. The main problem was again one of resolution. The export utilities
found in ArcView and LandSerf create vrml elevation grids from the GIS dataset, bit
it of a grid or TIN arrangement. This led to vast, unusable files (greater than 100Mb)
if the export resolution was set to high or poor levels of detail if the resolution was set
too low. Eventually, this led to the definition of a smaller study region as a
compromise in order to allow a sufficiently high resolution.

A major problem involved attaching the individually modelled monuments to the
land-surface. While the process was straightforward for the individual megaliths, the
process for the more complicated monuments, such as the enclosures and Henge, was
more subjective and less controlled involving the use of a conform space and much
manual adjustment of individual vertices. This resulted in the reconstruction being
less accurate than originally desired, with the barrows being modelled as generic
forms, the Henge and enclosures being modelled as banks only. This was considered
an acceptable compromise as the banks would have been the most prominent parts of
the monuments when viewed from around the landscape, the ditches being below
ground level and, thus, out of sight from the majority of the study region. It would
have definitely been worthwhile to investigate the ditches, especially the effects of
recutting on their visibility, as this would have been a significant factor but, as already
stated, time constraints did not allow for the modelling of every possible influencing
factor; so there was a necessity for prioritisation.

37


Using scripts to provide a dynamic link;

The use of scripting to form a dynamic way of generating views proved a little too
involved for the scope of this project, resulting in a rather more manual approach. The
Java program designed did indeed function correctly, but the intricacies of vrml script
nodes were not properly resolved, particularly with the additional problem of differing
implementations of the VRML97 standard by the different browsers available. As it
was possible to achieve comparable results by more manual means, the lack of a truly
dynamic link did not prove to be too compromising; one drawback was a limit on the
number of vrml viewpoints it was possible to create manually using the output from
the GIS, given the time constraints.

Figure 8: The same scene viewed in different browsers to show inconsistencies (Goodrick, 1997)

Indeed, the quality of the exported vrml world was far from perfect. The 3D
StudioMax export utility produced a model with a number of errors, including gaps
where surfaces did not meet properly, missing planes and a complete lack of textures.
In addition, the model does not always render correctly within the browser. While the
lack of textures was purely an aesthetic fault, not affecting the use of the model as an
investigative tool, the other faults did impinge on the usefulness of the system. A
potential solution to this issue would have been to use a dedicated vrml authoring
package, such as CosmoWorlds, which, having native support for vrml, produce much

38


better results than most commercially available 3D modelling packages, which work
using proprietary formats with a conversion option.

Presentation of results;

The presentation of the results in the form of animations based on the GIS output
and rendered views from the reconstruction proved very useful. While no direct
statements could be made regarding specific lines-of-sight or locations, the more
general experiential patterns could clearly be observed. In addition to walk-throughs,
animations along paths at observer height, the animations and renders from
viewpoints that would have been impossible proved useful in spotting alignments
between the monuments.

Unfortunately, the vrml world proved a less successful way of visualizing the
spatial dataset. Without the dynamic script link, it proved time-consuming to
construct and provided little or no advantage over the use of rendered images and
animations to corroborate the GIS output.

With respect to visualizing data as part of an analytical approach rather than a
purely aesthetic one, there a number of pieces of software available as plug-ins for 3D
StudioMax which allow highly detailed models to be exported as very small files
which can be viewed in a plug-in equipped browser with little or no degradation when
compared to the original. Originally designed for selling objects over the web, the
plug-ins allow the customer to spin the object round to see all sides, zoom in and out
and pan around. In addition to this, the WildTangent software has an additional
Software Development Kit available including a full API, allowing the user to fully
customise the product and integrate it with other systems making it possible to control
the visualization and use it for analytical purposes, as was attempted in this project.
While such proprietary systems do not comply to any form of internationally agreed
standards such as the VRML97 ISO standard, they do represent a much simpler way
of achieving accurate visualisations of three-dimensional reconstructions which, due
to the Development Kit, can easily be tailored to specific needs, such as having strict
control over the viewpoints, even from another application.

39


Conclusions

To conclude, this project has certainly been an interesting one to undertake and the
various strands have led to a number of conclusions regarding both the methodology
for analysing and visualizing three-dimensional spatial data as well as the positioning
and development of elements within the Avebury complex.

Archaeologically speaking, the results of the various analyses performed served to
demonstrate the significance of movement when dealing with the Avebury complex.
Thomas (1999) has already described the effect on perception of the course of the
West Kennet Avenue, and it is hoped that the results from this investigation go some
of the way at least towards a tentative interpretation of the Beckhampton Avenue.
Barnatt (1998) writes “A site’s impact can be emphasised both by careful architecture
and by careful placing. Thus, although a distant monument is visible, sometimes
spectacularly so as a skyline feature or because of strong colour contrasts with its
surroundings, its interior is hidden by a bank or mound. At other monuments a careful
choice of site makes them invisible until the participants approach, the impact
emphasised by their sudden appearance” (ibid. 96). The results from this project have
demonstrated these factors in operation: The Henge can be viewed from a number of
locations, but the inside is only revealed in the last stretch of the Beckhampton
Avenue approaching it; the Beckhampton enclosure was placed in a depression, a
pocket of low frequency on the cumulative viewshed analysis, causing it to be
shielded from view from much of the course of the Beckhampton Avenue; Silbury
Hill appears silhouetted against the horizon for much of the course of the Avenue,
only disappearing as one approaches the Cove and the area once occupied by the
enclosure.

Such an experiential account of the patterns of visibility associated with the
Beckhampton Avenue could, in part, explain the development of monuments in and
around Longstones Field, particularly the very short primary phase of the Cove and
the destruction of the earlier enclosure: As social meanings changed over time, it
became necessary to remodel the monuments to take into account new social
interpretations. Perhaps as the Neolithic progressed and more sedentary lifestyles
became prevalent, it became necessary to formalise the ancient route-way leading

40

Pathways through the Avebury Landscape; A study of spatial relationships associated with the Beckhampton Avenue, Avebury, Wilts.

Pathways through the Avebury Landscape; A study of spatial relationships associated with the Beckhampton Avenue, Avebury, Wilts.

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Pathways through the Avebury Landscape; A study of spatial relationships associated with the Beckhampton Avenue, Avebury, Wilts.