[gdal-dev] Geolocation arrays - location interpretation

[Agram, Piyush S (334D)]

Hi,
     I’m trying to track down systematic pixel shift effects observed with warping data using geolocation arrays:
https://trac.osgeo.org/gdal/ticket/6959

Essentially, the same data (image and location) provided as geolocation arrays is warped to a different output depending on how the arrays are laid out – WESN, WENS, EWSN, EWNS.
Gdalwarp produces least shift in warped data when the input arrays themselves are oriented WENS.

Is there a definitive definition for interpretation of lat,lon,value when geolocation arrays – i.e, are the lat/lon representative of pixel center (which I think should be the intent)?
Does GDAL by default assume that the geolocation value corresponds to the top/left of the pixel? Could this confusion result in the observed systematic shift?

Alternately, could the input arrays be reoriented to WENS using VRTs instead of rewriting large raster files?

Piyush
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