[gdal-dev] gdalwarp problems with MODIS L1B

[Even Rouault]

Rutger,

> 
> Maybe i'm missing something, but for as far as i know, the MODIS MOD021KM
> product is still a 'swath', and therefore still containing the bow-tie
> effect as the result of the scanning sensor. Wouldn't this mean that
> gdalwarp will never work? The lat/lon arrays aren't continuous, 

yes you're right. I looked at the first column of the latitude array, and the 
derivative apparently changes sign for each row,

>>> from osgeo import gdal
>>> ds = 
gdal.Open('HDF4_SDS:UNKNOWN:"MOD021KM.A2012062.0455.006.2014220083128.hdf":0')
>>> first_col = ds.ReadAsArray()[:,0]
>>> first_col[1:] - first_col[0:-1]
array([-0.07051849,  0.0051384 , -0.07039642,  0.00334167, -0.07026672,
        0.00508118, -0.07014084,  0.00319672, -0.07001114,  0.00492477,
       -0.06988907,  0.00340271, -0.06975555,  0.00507736, -0.06962967,
....

So yes I don't think the GDAL transformers can work properly with that kind of 
data.

On lines, the values look more continuous. So a potential workaround might be 
to reorder the lines of the raster and of the lat,lon arrays priorly to any 
warping.

Even

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