[Gdal-dev] convert HDF ASTER to geotiff

[Andrey Kiselev]

Jon,

On Mon, May 02, 2005 at 06:52:56AM -0700, Jon Saints wrote:
> Yes, I agree that ASTER's come with ground control points, however,
> when using gdal_translate it seems that the utility doesnt apply the
> ground points correctly.

gdal_translate will not apply the control points, that is the task for
special application called gdalwarp, gdal_translate just tries to
transfer as much information as possible between two different file
formats. gdalwarp will do the trasformation based on GCPs or
corners coordinates.

Aslo I am sure you are missed important point: you need GDAL from CVS to
get ASTER transformation working.

> My observation is this: In the raw aster image the corners (ul and lr)
> of the raw image data are not the "corners" of the data. Along both
> edges of the actual data there are no data values hold space as
> padding. The actual image data is a slanted trazezoid padded on both
> sides with no data values within the rectangle that is the raw aster
> image. gdal_translate can apply the GCP points to the raw image, but
> does so incorrectly. It applies the ul and lr values to the no data
> padding of the raw image, rather than applying the point to the actual
> corner where the actual data begins.  

There are two types of ASTERs. The first one is Level 1A. These scenes
contains a set of GCPs and no corner coordinates and should be
georeferenced by the some appropriate application (gdalwarp in our case)
before using. You do not have other way of using these data.

The second type is Level 1B/Level 2 datasets. These ones contain both
GCPs and corner coordinates (and rotation angle in addition); they are
already transformed. These scenes can be georeferenced using both ways:
GCPs and corners, results will be the same. I am prefer use the first
approach, i.e., GCPs, but when I tried georeferencing with the corners
result was the same. These two approaches are equal. And you can't
apply the corner coordinates directly, the scene must be rotated
(rotation angle provided in the metadata as well, but it is not actually
needed).

Anyway, gdalwarp should solve all you problems with ASTER data.

Best regards,
Andrey

PS.
There is also the third type of ASTER scenes, the DEM (Level 3). It is
georeferenced with GCPs, but sligtly differntly from the previous two
types.

-- 
Andrey V. Kiselev
Home phone:  +7 812 5970603  ICQ# 26871517