HDF AND HDF-EOS WORKSHOP II (1998) Source: http://hdfeos.org/workshops/ws02/presentations/ilg1/ilg1.ppt

1. An Overview of
HDF-EOS
(Part I)
Doug Ilg
Raytheon STX
Doug.Ilg@gsfc.nasa.gov
(301) 441-4089
1

2. Outline
What is HDF-EOS?
The Grid Interface
The Point Interface
2

3. What is HDF-EOS?
An HDF “Profile”
An extension to HDF
A library built “on top” of HDF
Three new data objects
Three new programming interfaces
3

4. Why HDF-EOS?
Standard HDF lacks well defined ways of
handling some key needs of EOSDIS
Data structures for Earth remote
sensing data and in-situ measurements
with:
– tightly coupled geolocation information
– subsetting services based on geolocation
ECS metadata model
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5. HDF-EOS Platforms
HDF-EOS Version 2.3 is available for:
Sun SPARC - Solaris
SGI - IRIX
DEC Alpha - Digital UNIX
HP 9000 - HP-UX
IBM RS/6000 - AIX
PC - Windows 95/NT
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6. HDF-EOS Interfaces
C and FORTRAN Interfaces for:
Grid Data (GD)
Point Data (PT)
Swath Data (SW)
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7. HDF-EOS Programming
Model
Writing
–
–
–
–
–
–
–
–
open file
create object
define structure
detach object*
attach object*
write data
detach object
close file
Reading
–
–
–
–
–
–
open file
attach object
inquire object
read data
detach object
close file
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8. A Grid Data Set
8

9. A Grid Structure
Xdim
Size: 2000
Projinfo
Ydim
Size: 800
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10. Projections Supported
Geographic
Transverse Mercator
Universal
Transverse Mercator
Hotine Oblique
Mercator
Space Oblique
Mercator
Polar Stereographic
Lambert Azimuthal
Equal Area
Lambert Conformal
Conic
Polyconic
Interrupted Goode’s
Homolosine
Integerized
Sinusoidal
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11. Components of the Grid
Interface
Access
Definition
Basic I/O
Inquiry
Subset
Tiling
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12. Tips on Writing a Grid
Order of calls is significant:
– Setting a compression method affects all
subsequently defined fields
– Setting a tiling scheme affects all
subsequently defined fields
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13. Grid Subsetting Features
By Geolocation
– GDdefboxregion/Gdextractboxregion
By “Vertical” Field
– GDdefvrtregion/GDextractvrtregion
By Time (special case of vertical)
Tip: use Geolocation, then Vertical/
Temporal
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14. Compression Methods for
Grids
Run-Length Encoding
Adaptive Huffman
Gzip
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15. A Point Data Set
Lat
61.12
45.31
38.50
38.39
30.00
37.45
18.00
43.40
34.03
32.45
33.30
42.15
35.05
34.12
46.32
47.36
39.44
21.25
44.58
41.49
25.45
Lon Temp(C) Dewpt(C)
-149.48 15.00 5.00
-122.41 17.00 5.00
-77.00 24.00 7.00
-90.15 27.00 11.00
-90.05 22.00 7.00
-122.26 25.00 10.00
-76.45 27.00 4.00
-79.23 30.00 14.00
-118.14 25.00 4.00
-96.48 32.00 8.00
-112.00 30.00 10.00
-71.07 28.00 7.00
-106.40 30.00 9.00
-77.56 28.00 9.00
-87.25 30.00 8.00
-122.20 32.00 15.00
-104.59 31.00 16.00
-78.00 28.00 7.00
-93.15 32.00 13.00
-87.37 28.00 9.00
-80.11 19.00 3.00
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16. A Point Structure
Lat
Long
Buoy ID
25.2645 091.2564
0126
22.3549 -93.4657
3564
23.2564 -89.2546
1256
Buoy ID
0126
0126
3564
1256
1256
0126
3564
Time Wave Height(ft) Temp(C)
01:26
2.54
18.4
05:56
3.58
18.2
06:28
12.64
16.4
08:12
7.58
17.1
09:58
7.76
17.2
09:59
4.23
20.1
10:16
10.23
17.5
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17. The Point Interface
Access
Definition
Basic I/O
Inquiry
Subset
17

18. Tips on Writing a Point
Every level in a Point data set must be
linked into the hierarchy.
Before two levels can be linked, a link
field must exist.
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19. Point Subsetting Features
By Time
– PTdeftimeperiod/PTextractperiod
By Geolocation
– PTdefboxregion/PTextractregion
Tip: use one or the other, not both
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20. Compression Methods for
Points
NONE
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21. Tips for HDF-EOS Coding
Most operations (read, write, subset)
work on a single field at a time.
Region IDs and Period IDs are interchangeable and can be reused to
further reduce a subset.
Partial writes (appending) on
compressed fields are only supported
through tiling.
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