The document provides an overview of HDF-EOS, an extension of HDF designed for Earth science data management, including features like geolocation and data subsetting. It details the programming interfaces and data structures for grid and point data sets, outlines supported projections, and offers tips for implementation and coding. Additionally, it highlights the platforms for HDF-EOS version 2.3 and discusses compression methods for both grid and point data.

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
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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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