[gdal-dev] Status of RFC 4: Geolocation Arrays especially Envisat wrt GCPs

[Brent Fraser]

Frank,

The short story:

  I've got some Single Look Complex EnviSat data I need to process.  Will gdalwarp do a piecewise (triangulated) warp using GCPs or only(!) use them to calculate an image-wide polynomial?

The longer story:
	ESA's Best (http://earth.esa.int/services/best/) does an OK job extracting the amplitude from the data, but because it uses tiff files for intermediate storage, and their implementation is limited to 2gb tiffs, it's necessary to tile an input image.  Best assigns a different affine transformation to each output GeoTiff tile, which causes a mis-alignment of the tiles when re-assembling them (using gdalwarp etc).  Best does output an extensive metadata text file with each tile including a geolocation "array" of latitude and longitude.  Unfortunately the "array" is not regular (eg, my test tile has values for lines 1, 811, 812, 1622, 1623, 2240; every 165 pixels except the last interval which is 195 pixels).  If gdalwarp would use this semi-regular array to triangulate the pixel locations, that would be great, otherwise I'll have to use something else...

Thanks!
Brent Fraser