[FWTools] gdalwarp and image rotation

[Tom Webster]

I wish to rotate a typical image (resolution 25m, UTM) for 30 degrees and perform some pixel-level analysis, and then re-rotate back to north-up. In all these, I wish to keep the pixel resolution intact. 

I tried the following:

1. use gdal_translate to produce a baseline TIFF file (x.tif) and a worldfile(x.tfw)
2. modify the worldfile and specify the degrees to be changed
3. use gdalwarp to make the first rotation: gdalwarp x.tif y.tif
however, in this step, the 'pixel resolution' is changed, something close to 100. If I still specify -tr 25 25 in the gdalwarp commandline, then the size of the output is getting very large, close to 4 x 4 times larger. I guess gdalwarp assumes the x.tif has a 'resolution' of 100 in this regard. I lost here and hope someone can help me. Really appreciate any help and advice.








      
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