[Gdal-dev] HDF control point dump for Aster DEM (and Modis)

[Andrey Kiselev]

On Thu, Feb 12, 2004 at 02:01:23PM -0700, Brent Fraser wrote:
>   I'm looking into control points in HDF files again, this time for
>   Aster DEMs.  Can gdalinfo or gdal_translate dump the control points
>   as text to the screen?
> 
> Some background...
> 
> I've downloaded an Aster DEM from the EOS Data Gateway
> (http://edcimswww.cr.usgs.gov/pub/imswelcome/) and translated it to
> GeoTIFF with gdal_translate.  For comparison, I also translated it
> GeoTIFF using HEG
> (http://hdfeos.gsfc.nasa.gov/hdfeos/details.cfm?swID=59).  The
> positioning of HEG's GeoTIFF was accurate to about 200m (compared to
> 1:250k VMAP1 vector data), while GDAL's was out by about 2 kilometers.
> 
> I expect the difference is due to HEG using the 8 x 8 array of control
> points in the HDF file.  I've got a program that will use the points
> to warp the DEM using triangulation, but I don't have an easy way to
> get a list of the gcps.
> 
> I used to HDFview (http://hdf.ncsa.uiuc.edu/hdf-java-html/hdfview/) to
> see how the gcps are stored in the HDF file, and it's not simple.
> Under "Geolocation Fields", it's a single grid named as
> MRGFLD_Latitude, as a single three-dimensional (2 x 8 x 8) array of
> 64-bit floats (64 gcps with lat in the first plane and lon in the
> second).  This is significantly different from Modis HDF gcps which
> are stored as 2 two-dimensional arrays(one Latitude, the other
> Longitude) of 32-bit floats.
> 
> Given the popularity of Aster DEMs and Modis data it might make for a
> nice enhancement to gdalinfo to dump the gcps for these two types of
> HDF datasets...

Brent,

I'm working on the new HDF driver driver which will be much better than
the current one. New driver will be based on HDF-EOS code and will be
able to work properly with wider range of HDF products. I have
implemented support for HDF-EOS Grid datasets (MODIS L2 products) and
have implemented partial support for Swath datasets (different ASTERs,
MODIS L1 and L3 etc.) Unfortunately it is not possible to support all
products without hardcoding their parameters into the driver.

I'm aware of the deficiences of ASTER DEM supporting, but it should be
fixed in the new driver version. Stay tuned, it will be available very
soon.

					Andrey

-- 
Andrey V. Kiselev
Home phone:  +7 812 5274898  ICQ# 26871517