[Gdal-dev] Re: AVHRR NOAA level 1b

[Juan Castaneda]

We have a receiver and download images continously. The software we have
produces level 1b images and can export to .img. Those img are correctly
geocoded and they work fine. But I cannot set that software up to create
.img images for each l1b produced. So I thaught GDAL would do the work.

I have tryed using gdalwrap -tps but it doesn't seem to work. It
produces errors of 600Km... it's way too much. I'm more like a GIS guy
so I took the GCPs from gdalinfo and using ArcGIS I attempted to
geocode. It produced pretty much the same results as gdal. I'm wondering 
if I am missing something! should I have to apply some other correction? 
Maybe I am taking the same assumptions as gdalwrap and they are wrong. 
Maybe the GCPs read from gdal are not correct.

I appreciate any thoughts

Juan C

Markus Neteler wrote:

> On Fri, May 19, 2006 at 09:58:50AM +0100, Juan Carlos Castaneda
> wrote:
> 
>> Dear list,
>> 
>> I'm trying to use GDAL to geocode AVHRR level 1b images. It's not
>> giving me good results. I went to the archives and Google to find
>> what's happening and I read that the algorithm to geocode is not
>> the best for these type of image. From the documentation: "that
>> GDAL simple affine georeference model completely unsuitable for the
>> NOAA data. So you should not rely on it. It is recommended to use 
>> the thin plate spline warper (tps). Automatic image rectification
>> can be done with ground control points (GCPs) from the input file.
>> NOAA stores 51 GCPs per scanline both in the LAC and GAC datasets."
>> 
>> 
>> Any suggestions how to do the "thin plate spline warper (tps)" for
>> these images? Can it be done with GDAL? I've used gdalwrap -tps but
>> it's not working neither. I used the GCPs and they don't seem to
>> give accurate positions on the image. Can anybody give me some
>> advice?
> 
> 
> Please use gdalwarp with -tps option:
> 
> http://www.gdal.org/gdalwarp.html "-tps Enable use of thin plate
> spline transformer based on available GCPs. Use this instead of the
> -order switch. "
> 
> Please let us know how it performs (I am also interested in the AVHRR
> geocoding business).
> 
> Markus