[FWTools] MODIS processing

Frank Warmerdam warmerdam at pobox.com
Wed Jan 4 17:01:18 EST 2006

On 1/4/06, Ned Horning <nedh at lightlink.com> wrote:
> Frank,
> First the good news. Using -s_srs "WGS84" fixed the problem.
> Now the bad news. The resulting image is poorly projected. After digging
> into this a bit it seems as if the initial GCP assignment might not be
> accurate. I noticed this when I loaded the HDF image into OpenEV_FW and
> checked the coordinates of some points around the image (using the cursor
> and overlaying a shapefile) and the coordinates were off 10's of kilometers.
> I would expect these coordinates to be quite accurate. The processing also
> took about 20 minutes for each image I supposed because there were so many
> GCPs. When I ran gdalwarp on some Landsat images it was lighting fast.


The problem with locations being off by large amounts is likely
something that Andrey would need to look into.

> I used ENVI to project the same file and that result looks fine so I'm
> pretty sure the data is okay (or at least as ok as HDF data ever gets). In
> any case, I uploaded a sample HDF file, the output from gdalwarp (band 1
> only), the output from ENVI, and a screen shot with a vector overlay on the
> HDF image in OpenEV_FW. These are all on my ftp site:
> ftp://ftp.amnh.org/pub/people/horning/downloads/MODIS
> Any thoughts before I start looking into other options?

Nope, I'm not convinced we will be able to provide a quick solution.

> One more question. Is it possible to project two images without doing
> interpolation using gdalwarp? In other words can you do a rigorous
> transformation using all pixels rather than interpolating between points or
> applying a polynomial?

It is my intention to implement warping support in gdalwarp
that uses the full data available in geolocation arrays at some
point.  But I'm not sure when I will get to that.

Best regards,
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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