BASIC CONCEPTS OF PHOTOGRAMMETRY

1. NAMITHA M. R.
ID. No: 2015664502
M. Tech, LWME
TNAU
BASIC PRINCIPLES OF
PHOTOGRAMMETRY

2.  Science and technology of obtaining spatial measurements
and other geometrically reliable derived products from
photographs
Photogrammetry

3.  Analysis procedures ranges form obtaining approximate
distances, areas and elevations using hardcopy photographic
products, unsophisticated equipment and simple geometric
concepts to generating precise Digital Elevation Models
(DEMs), orthophotos, thematic GIS data and other derived
products through the use of digital raster images and
relatively sophisticated analytical techniques
Contd…

4.  Photogrammetric operation involving the use of digital
raster photogrammetric image data – Digital / Softcopy
photogrammetry
 Most common use of photogrammetry- To produce
hardcopy topographic maps
Contd…

5.  Determining the scale of a vertical photograph and
estimating the horizontal ground distances
 Using area measurements made on a vertical photograph to
determine the equivalent areas in a ground coordinate
system
 Quantifying the effect of relief displacement on vertical
areal photographs
Photogrammetric
activities

6.  Determining object heights from relief displacement
measurements
 Determining object heights and terrain elevations by
measuring image parallax
 Using ground control points
 Producing maps and orthophotos
 Preparing a flight plan to acquire aerial photography
Contd…

7.  Geometric types of aerial photographs :-
i. Vertical photographs:
• Made with the camera axis directed as vertically as possible
• Unavoidable tilts cause slight (1° to 3°) unintentional
inclination of the camera optical axis- Tilted photographs
Basic Geometric Characteristics Of Aerial
Photographs

8. ii. Oblique photographs:
• Aerial photographs taken with intentional inclination of the
camera axis
• High oblique photographs include an image of the horizon
and low oblique photographs do not.
Contd…

9.  Taking vertical aerial photographs :-
• Mostly taken with flight cameras along the flight lines or flight
strips
• Nadir line- Line traced on the ground directly beneath the aircraft
during acquisition of photography
• Successive photographs are generally taken with some degrees of
end lap
• An end lap of 50% is essential for total stereoscopic coverage of a
project area
Contd…

10. Contd…

11. • Stereoscopic coverage consists of adjacent pairs of
overlapping vertical photographs called stereo pairs
• Stereo pairs provides 2 different perspectives of the ground
area in their region of end lap
• When stereo pairs are viewed through a stereoscope, the
result is the perception of a 3D stereo model
Contd…

12. • Intervalometer: Device that automatically trips the camera
shutter at desired time intervals.
• Stereoscopic overlap area: Area included in the overlap of
successive photographs
• Air base: Ground distance between the photo centers at the
times of exposure
Contd…

13. • The ratio between the airbase and the flying height above
ground determines the vertical exaggeration perceived by
photo interpreters
• Larger the base-height ratio, greater the vertical
exaggeration
Contd…

14. • Adjacent strips are provided with a side lap of 30%
• Multiple strips comprise what is called a block of
photographs
Contd…

15. Contd…

16.  Geometric elements of a vertical photograph:-
Contd…

17. • Light rays from terrain object  Camera lens exposure
station(L)  Plane of the film negative
• The negative is located behind the lens at a distance equal to
the lens focal length, f
• Paper print positive image positions can be depicted
diagrammatically in front of the lens in a plane located at a
distance, f
Contd…

18. • The x axis coincides with the line of flight and the y axis
is located 90° counter clockwise from the positive x axis
• Photo coordinate point o is assumed to coincide with the
principal point
• Principal point - Intersection of lens optical axis and the
film plane
Contd…

19. • Ground principal point, (O)– Point where the prolongation
of the optical axis of the camera intersects the terrain
• Images for terrain points A, B, C, D and E appear
geometrically reversed on the negative at a’, b’, c’, d’ and e’
and in proper geometric relationship on the positive at a, b,
c, d and e
Contd…

20.  Photo coordinate measurement:-
• Engineer’s scale or metric scale
• Coordinate digitizer
• Comparator – Mono comparator or Stereo comparator
Contd…

21.  The relationship between the photograph’s row and column
coordinate system and the camera’s fiducial axis
coordinate system is determined by a mathematical
coordinate transformation between the 2 systems
Contd…

22.  An expression that states that one unit of distance on the
photograph represents a specific number of units of actual
ground distance
 Expressed as unit equivalents, representative fractions or
ratios
Photographic Scale

23.  Larger scale shows ground features at a larger, more
detailed size (eg: 1:10000)
 Smaller scale shows ground features at a smaller, less
detailed size (eg: 1:50,000)
 Same objects are smaller on a smaller scale photographs
than on a larger scale photographs
Contd…

24.  Scale S is computed as the ratio of photo distance d to the
ground distance D,
Photo Scale, S =
𝑷𝒉𝒐𝒕𝒐 𝑫𝒊𝒔𝒕𝒂𝒏𝒄𝒆
𝑮𝒓𝒐𝒖𝒏𝒅 𝑫𝒊𝒔𝒕𝒂𝒏𝒄𝒆
=
𝒅
𝑫
 For a vertical photograph taken over a flat terrain, scale is a
function of focal length f of the camera and the flying height H’
above the ground,
Scale =
𝑪𝒂𝒎𝒆𝒓𝒂 𝑭𝒐𝒄𝒂𝒍 𝑳𝒆𝒏𝒈𝒕𝒉
𝑭𝒍𝒚𝒊𝒏𝒈 𝑯𝒆𝒊𝒈𝒉𝒕 𝒂𝒃𝒐𝒗𝒆 𝑻𝒆𝒓𝒓𝒂𝒊𝒏
=
𝒇
𝑯′
Contd…

25.  Average scale computed for the entire photograph,
Savg =
𝒇
𝑯−𝒉𝒂𝒗𝒈
where, havg  Average elevation of the terrain
Contd…

26. Contd…

27.  All points on a map are depicted in their true relative
horizontal positions, but points on photo taken over varying
terrain are displaced from their true map positions
 Result of photo scale variation- Geometric distortion
 Map is a scaled Orographic projection of the ground,
whereas a vertical photograph yields a Perspective
projection
Contd…

28. Contd…

29.  On a map  Top view of the object are seen in their true
relative horizontal positions
 On a photo  Areas of the terrain at the higher elevations
appear larger than corresponding areas lying at lower
elevations. top of the objects are always displaced from
their bases
 This distortion is called Relief displacement
Relief Displacement

30.  Causes any object standing above the terrain to lean away
from the principal point of a photograph radially
Contd…

31.  Relief displacement,
d =
𝒓𝒉
𝑯
where, r  radial distance on the photograph from the
principal point to the displaced image point
h height above datum of the object point
H  flying height above the same datum chosen to
reference h
Contd…

32.  Parallax – Apparent change in relative positions of
stationary objects caused by a change in viewing positions
 This phenomenon is observable when one looks at objects
through the side window of a moving vehicle
Image Parallax

33. THANK YOU