Hi Chatinya, Thanks for the advice - I've definitely ensured that the file does not exist first, cleared it out and re-ran gdal_merge.py. The result still has the same clipping to 255.
-mike. On May 15, 2011, at 9:19 PM, Chaitanya kumar CH wrote: > Michal, > > Check if the output file already exists. The script won't create a new one if > it already exists. > > On Mon, May 16, 2011 at 12:45 AM, Michal Migurski <[email protected]> wrote: > Hello, > > I'm attempting to merge a number of DEMs in .flt format using gdal_merge.py. > It's NED 1/3 arc second data, so each one is a Float32 10812x10812 raster > with a range of values from a few meters below sea level to 1.4km. I'm > getting back an image with an incorrect datatype even though I believe that > I'm using the right "-ot Float32" parameter to gdal_merge.py. I appear to > have gdal 1.5.4 on this machine; I can upgrade to a newer one if necessary > but I'd first like to make sure I'm not using the tool incorrectly. > > Here's the command I use: > > gdal_merge.py -o 38122.tif -of GTiff -ot Float32 -v -ul_lr -122.05 > 38.05 -121.95 37.95 10m/*.flt > > What I get back is a 1080x1080 GeoTIFF with the correct bounds that I'm > expecting, but what appears to be garbage data or perhaps just raw floating > point values misinterpreted as bytes. Here's the output showing Byte values > instead of Float32 as I'd expect: > > Band 1 Block=1080x7 Type=Byte, ColorInterp=Gray > Min=0.000 Max=255.000 > Minimum=0.000, Maximum=255.000, Mean=108.657, StdDev=66.615 > > This is a sample of the resulting image in pseudocolor, showing the vertical > banding every 4px that makes me think the bytes are just a raw Float32 stream: > > http://mike.teczno.com/img/38122-rainbow.png > > Here is a sample input band: > > Band 1 Block=10812x1 Type=Float32, ColorInterp=Undefined > Computed Min/Max=-8.170,1440.937 > NoData Value=-9999 > > Am I using -ot incorrectly? > > -mike. > > ---------------------------------------------------------------- > michal migurski- [email protected] > 415.558.1610 > > > > _______________________________________________ > gdal-dev mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/gdal-dev > > > > -- > Best regards, > Chaitanya kumar CH. > /tʃaɪθənjə/ /kʊmɑr/ > +91-9494447584 > 17.2416N 80.1426E ---------------------------------------------------------------- michal migurski- [email protected] 415.558.1610 _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
