agnes123 wrote:
Dear all,
i have one question on the default pixel size in gdalwarp.
In gdalwarp, we can use -tr to determine output pixel size in x and y
direction, however, if i omit the argument -tr , gdal will have a default
pixel size value which is in target projection units.
For example, if the orginal input raster which has geodetic projection with
pixel size 0.000277778 (decimal degree), after projecting to Lambert
Conformal Conic without typing the argument -tr, gdal will have output
raster pixel size 28.793808m. What is the algorithm behind to obtain the
value 28.793808?
I was wondering if there is somebody who knows it. I would greatly
appreciate it.Thanks!
Regards,
Agnes
Agnes,
The computation is done by the GDALSuggestedWarpOutput2() function. I would
suggest you read it's documentation and if still in doubt scan through the
code.
http://trac.osgeo.org/gdal/browser/trunk/gdal/alg/gdaltransformer.cpp#L162
It is basically a heuristic to maintain approximately the same diagonal
size of a pixel in the destination coordinate system as it was in the
source coordinate system.
Best regards,
--
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