[GRASS-user] MODIS HDF conversion in TIF tool.

[Hamish]

Ivan Shmakov wrote:
>  >> Reprojecting and subsetting of HDF-EOS grid data is, indeed,
>  >> straight-forward, and usually could be done with, e. g.,
>  >> gdalwarp(1).  Not so for the swath data.
> 
>  > Could the swath data be reprojected using gdalwarp's -tps thin plate
>  > spline function? ISTR that's what -tps was commisioned for. (??)
> 
> 	I've tried gdalinfo(1) on AIRS .hdf:
> 
> $ gdalinfo AIRS.2007.05.31.214.L2.RetStd.v4.0.9.102.D07281163221.hdf
> 
> 	and it shows no ground control points.  I suppose, this is
> 	because the GCP's are given in separate HDF arrays (Latitude &
> 	Longitude), and not in the metadata.  Solving this problem may
> 	make gdalwarp(1) an alternative to HEG.

you can use gdal_translate to add (per scanline) GCPs to the metadata before
running gdalwarp.
 gdal_translate  -gcp pixel line easting northing [elevation]


> 	The one more problem with the MODIS L2 data is that it consists
> 	of overlapping scans -- MODIS could ``see'' some parts of the
> 	Earth in consequent scans.  Like this (intended to be viewed
> 	with a monospace font):
> 
>    +--....                                             ....--+
>    |      `~~~-----....                    ....----~~~'      |
>    |                   `~~~~~--------~~~~~'                  |
>    |                                                         |
>    |                                                         |
>    +--....                                             ....--+
>    |......`~~~-----....                    ....----~~~'......|
>    |...................======--------======..................|
>    |......,...-----~~~'                    `~~~----..........|
>    +--~~~~                                             ~~~~--+
>    |                                                         |
>    |                                                         |
>    |                   ......--------......                  |
>    |      ,...-----~~~'                    `~~~----....      |
>    +--~~~~                                             ~~~~--+
> 
>         (Areas filled with periods are the ones which MODIS ``sees''
>         twice per orbit.)


I think you may get a much better answer about this if you ask on the gdal-dev
mailing list. (www.gdal.org)  Lots of smart experts on this stuff there.


Hamish



      ____________________________________________________________________________________
Never miss a thing.  Make Yahoo your home page. 
http://www.yahoo.com/r/hs