[gdal-dev] GDAL Cubic Interpolation

[Harvey Berger]

Hi,

I subsampled a GLOBE image of elevation data by a subsampling factor of 12
to a resolution of 0.1 deg x 0.1 deg on integer multiples of 0.1 deg. The
original GLOBE image is: Latitude from +90-1/240 deg to -90+1/240 deg in
1/120 deg steps, and Longitude from -180+1/240 deg to +180-1/240 deg in
1/120 deg steps.

I understand that the cubic interpolation method in gdalwarp accounts for
the subsampling factor, so 48x48 adjacent pixels influence the target pixel
for a subsampling factor of 12.

Does gdalwarp assume the original image is a sphere, where 48x48 adjacent
pixels influence all target pixels, or a rectangle, where a limited number
of pixels influence the target pixels at the top, bottom, left, and right
edges of the subsampled image? If gdalwarp assumes the original image is a
rectangle and uses a modified interpolation method at the four edges of the
subsampled image, the modified method affects two rows and two columns at
the top, bottom, left and right edges of the subsampled image. If gdalwarp
assumes the original image is a rectangle, is there a command option so
gdalwarp considers spherical wrapping when interpolating? Alternatively, I
assume I could augment the original GLOBE image with the appropriate
additional rows and columns on all four edges. If I did that, how do I tell
gdalwarp the extent of the augmented input image?

Kind regards,

Harvey
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