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

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

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

4. 4 Standard HDF lacks well defined ways of handling some key needs of EOSDIS Why HDF-EOS? n Data structures for Earth remote sensing data and in-situ measurements with: –tightly coupled geolocation information –subsetting services based on geolocation n ECS metadata model

5. 5 HDF-EOS Platforms HDF-EOS Version 2.3 is available for: n Sun SPARC - Solaris n SGI - IRIX n DEC Alpha - Digital UNIX n HP 9000 - HP-UX n IBM RS/6000 - AIX n PC - Windows 95/NT

6. 6 HDF-EOS Interfaces C and FORTRAN Interfaces for: Grid Data ( GD ) Grid Data ( GD ) Point Data ( PT ) Point Data ( PT ) Swath Data ( SW ) Swath Data ( SW )

7. 7 HDF-EOS Programming Model n Writing –open file –create object –define structure –detach object* –attach object* –write data –detach object –close file n Reading –open file –attach object –inquire object –read data –detach object –close file

8. 8 A Grid Data Set

9. 9 Xdim Size: 2000 Ydim Size: 800 Projinfo A Grid Structure

10. 10 Projections Supported n Geographic n Transverse Mercator n Universal Transverse Mercator n Hotine Oblique Mercator n Space Oblique Mercator n Polar Stereographic n Lambert Azimuthal Equal Area n Lambert Conformal Conic n Polyconic n Interrupted Goode’s Homolosine n Integerized Sinusoidal

11. 11 Components of the Grid Interface n Access n Definition n Basic I/O n Inquiry n Subset n Tiling

12. 12 Tips on Writing a Grid n Order of calls is significant: –Setting a compression method affects all subsequently defined fields –Setting a tiling scheme affects all subsequently defined fields

13. 13 Grid Subsetting Features n By Geolocation –GDdefboxregion/Gdextractboxregion n By “Vertical” Field –GDdefvrtregion/GDextractvrtregion n By Time (special case of vertical) n Tip: use Geolocation, then Vertical/ Temporal

14. 14 Compression Methods for Grids n Run-Length Encoding n Adaptive Huffman n Gzip

15. 15 A Point Data Set

16. 16 A Point Structure

17. 17 The Point Interface n Access n Definition n Basic I/O n Inquiry n Subset

18. 18 Tips on Writing a Point n Every level in a Point data set must be linked into the hierarchy. n Before two levels can be linked, a link field must exist.

19. 19 Point Subsetting Features n By Time –PTdeftimeperiod/PTextractperiod n By Geolocation –PTdefboxregion/PTextractregion n Tip: use one or the other, not both

20. 20 Compression Methods for Points n NONE

21. 21 Tips for HDF-EOS Coding n Most operations (read, write, subset) work on a single field at a time. n Region IDs and Period IDs are inter- changeable and can be reused to further reduce a subset. n Partial writes (appending) on compressed fields are only supported through tiling.