Harvey, > > 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?
A rectangle, with fallback to bilinear resampling at edges > 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? Nothing directly straightforward. Your below plan is the a reasonable solution. > 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? You'll have to recreate a properly referenced input image, for example with gdal_translate -ullr upperleftx upperlefty lowerleftx lowerlefty Even -- Spatialys - Geospatial professional services http://www.spatialys.com
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