gdalwarp very slow at updating big rasters, even if a small part is changed

[redl]

Hi,

gdalwarp is very slow when the output is a big already existing raster, even if only a small part has to be updated (by providing a cutline).

gdalwarp -cutline C:/cutline.csv C:/source.tif C:/target.tif

This takes over 45 seconds to process. To compare, copying the target.tif through gdal_translate takes around 30 seconds.

If I crop target.tif to the small part affected by the cutline, this executes in less than 1 sec. So it's clearly not the actual wrapping that is slow, but there's something in the save method.

It seems it's rewriting the whole raster, where as this is obviously unnecessary in case of updating an existing raster !

Thanks