[gdal-dev] Attempting to merge DEMs with gdal_merge.py - getting Float32 clipped to 255.0

[Chaitanya kumar CH]

Michal,

I can't think of anything else that may be causing this. Can you run this
using the latest version, gdal-1.8?

On Mon, May 16, 2011 at 11:14 PM, Michal Migurski <mike at stamen.com> wrote:

> Hi Chaitanya,
>
> 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 <mike at stamen.com>
> 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- mike at stamen.com
> >                 415.558.1610
> >
> >
> >
> > _______________________________________________
> > gdal-dev mailing list
> > gdal-dev at lists.osgeo.org
> > http://lists.osgeo.org/mailman/listinfo/gdal-dev
> >
> >
> >
> > --
> > Best regards,
> > Chaitanya kumar CH.
> > /tʃaɪθənjə/ /kʊmɑr/
> > +91-9494447584
> > 17.2416N 80.1426E
>
> ----------------------------------------------------------------
> michal migurski- mike at stamen.com
>                 415.558.1610
>
>
>
> _______________________________________________
> gdal-dev mailing list
> gdal-dev at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>



-- 
Best regards,
Chaitanya kumar CH.
/tʃaɪθənjə/ /kʊmɑr/
+91-9494447584
17.2416N 80.1426E
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