[gdal-dev] Georeferencing and reprojecting geostationary images

[Even Rouault]

Le mercredi 21 novembre 2012 18:46:59, Tobias Lohner a écrit :
> Hi List,
> 
> I'd like to reproject EUMETSAT EView (geostationary weather satellite)
> images to EPSG:3857 (aka web mercator), but I only got jpeg files
> without any georeference.
> 
> I tried to add several (up to 16 more or less) equally distributed
> ground control points to the image using gdal_transform and warping the
> result with gdalwarp:
> 
> # add gcps
> gdal_translate -gcp x y lon lat [...] image.jpg output.tiff
> # convert the image to EPSG:3857
> gdalwarp -t_srs EPSG:3857 output.tiff output_3857.tiff
> 
> Using third order warping or the thin plate transformer produces a
> reprojected image which doesn't fit to the target coordinate system,
> especially the corners are off by 0.1 to 0.3 degrees.
> 
> Is it possible to tell gdal that the source images are in geostationary
> satellite view (geos projection) for reprojecting them?

You can add -a_srs "+proj=geos [...]" on the gdal_translate command line (or -
s_srs on gdalwarp) if the GCP you specify are in coordinates compatible with 
the geos projection. In your example if you specify lon,lat, you'd likely want 
to use EPSG:4326.

The third order warping is known to suffer from numerical instability. Perhaps 
try second order with -order 2. The TPS warper should have a perfect fit on the 
GCPs

> 
> 
> Tobias Lohner
> 
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