Geolocation map X offsets in modis lib 250m and 500m producs are a half pixel off
|Reported by:||winkey||Owned by:||warmerdam|
The modis products have a fraction stored in another location that hdf-eos SWinqmaps() does not report.
MODIS Level 1B Product User's Guide page 14 http://mcst.gsfc.nasa.gov/uploads/files/M1054.pdf
"dimension maps, which define the relationship between the data fields and the geolocation fields. When the geolocation dimensions have a different size than the data dimension, an offset and an increment define the relation between them. These maps have been described as "the glue that holds the swath together." Unfortunately, the HDFEOS offsets are required to be integers, and the center of the first 1km geolocation pixel is offset by 1.5 250m pixels in the track direction from the first 250m data pixel. Therefore, the MODIS project requires that HDFEOS offsets be supplemented by a separate Fractional Offset file attribute, for each dimension map, that is to be added to the HDFEOS offset to get the true value."