[Gdal-dev] r.out.gdal vs gdal_translate vs gdalwarp

[Maciej Sieczka]

Hi

I have noticed that analogous options settings in r.out.gdal,
gdal_translate and gdalwarp result in GeoTIFF's of significantly
different sizes. Sorry for crossposting, but I have no idea if it is
and issue in GDAL or GRASS.

Take the following example, based on GRASS spearfish60 location, raster
elevation.dted:

$ r.out.gdal in=elevation.dted format=GTiff type=Byte out=grass_copy.tif

	grass_copy.tif = 36965 bytes

$ gdal_translate grass_copy.tif grass_trans_copy.tif

	grass_trans_copy.tif = 29153 bytes

$ gdalwarp grass_copy.tif grass_warp_copy.tif

	grass_warp_copy.tif = 36336 bytes

Each command does only a raw copy of input. Sizes of the r.out.gdal and
gdalwarp outputs are similar, but the gdal_translate output is 1/6
smaller. Is that normal?



Another example, with LZW compression:

$ r.out.gdal in=elevation.dted format=GTiff type=Byte out=grass_lzw.tif
createopt=COMPRESS=LZW

	grass_lzw.tif = 23497 bytes

$ gdal_translate -co "COMPRESS=LZW" grass_copy.tif grass_trans_lzw.tif

	grass_trans_lzw.tif =  21601 bytes

$ gdalwarp -co "COMPRESS=LZW" grass_copy.tif grass_warp_lzw.tif

	grass_warp_lzw.tif = 22868 bytes

Differences between the 3 tiffs here are not huge, yet still
significant. Is that OK? I thought each should be more less the same.



The only difference in the gdalinfo output of each of the 3 tiffs in
either the first or second example is 7 lines of metadata, which are
present in r.out.gdal and gdal_translate output while missing in
gdalwarp output. However, it is only 397 bytes, which is not enough to
explain kilobytes of differences.

Maciek