[Gdal-dev] GTOPO30 and max value

[Markus Neteler]

On Wed, May 30, 2007 at 12:56:35PM -0400, Frank Warmerdam wrote:
>  Markus Neteler wrote:
> > Hi,
> > should GDAL read the GTOPO30 data properly?
> > gdalinfo -mm W100N40.DEM
> > Driver: EHdr/ESRI .hdr Labelled
> > Size is 4800, 6000
> > Coordinate System is:
> > GEOGCS["WGS 84",
> >     DATUM["WGS_1984",
> >         SPHEROID["WGS 84",6378137,298.257223563,
> >             AUTHORITY["EPSG","7030"]],
> >         TOWGS84[0,0,0,0,0,0,0],
> >         AUTHORITY["EPSG","6326"]],
> >     PRIMEM["Greenwich",0,
> >         AUTHORITY["EPSG","8901"]],
> >     UNIT["degree",0.0174532925199433,
> >         AUTHORITY["EPSG","9108"]],
> >     AXIS["Lat",NORTH],
> >     AXIS["Long",EAST],
> >     AUTHORITY["EPSG","4326"]]
> > Origin = (-100.000000000000000,39.999999999999993)
> > Pixel Size = (0.008333333333330,-0.008333333333330)
> > Corner Coordinates:
> > Upper Left  (-100.0000000,  40.0000000) (100d 0'0.00"W, 40d 0'0.00"N)
> > Lower Left  (-100.0000000, -10.0000000) (100d 0'0.00"W, 10d 0'0.00"S)
> > Upper Right ( -60.0000000,  40.0000000) ( 60d 0'0.00"W, 40d 0'0.00"N)
> > Lower Right ( -60.0000000, -10.0000000) ( 60d 0'0.00"W, 10d 0'0.00"S)
> > Center      ( -80.0000000,  15.0000000) ( 80d 0'0.00"W, 15d 0'0.00"N)
> > Band 1 Block=4800x1 Type=UInt16, ColorInterp=Undefined
> >   Min=-9999.000 Max=6710.000   Computed Min/Max=1.000,55537.000
> >   Minimum=-9999.000, Maximum=6710.000, Mean=-6078.800, StdDev=5044.200
> >   NoData Value=-9999
> > -> Computed Min/Max=1.000,55537.000
> > is confusing me. Maybe a bug in the data set?
> 
>  Markus,
> 
>  It would be helpful to see the .HDR file.  It seems likely that the
>  data is actually signed 16bit integer, but being interpreted as
>  unsigned 16bit integer.  EHDR .HDR files are notoriously underspecified.
>  I think when used with Arc/Info there was some information (like pixel
>  type) that was passed on the commandline or something.
>

Frank, 

it looks like this:

cat W100N40.HDR
BYTEORDER      M
LAYOUT       BIL
NROWS         6000
NCOLS         4800
NBANDS        1
NBITS         16
BANDROWBYTES         9600
TOTALROWBYTES        9600
BANDGAPBYTES         0
NODATA        -9999
ULXMAP        -99.99583333333334
ULYMAP        39.99583333333333
XDIM          0.00833333333333
YDIM          0.00833333333333

Best,
Markus

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ITC -> dall'1 marzo 2007 Fondazione Bruno Kessler
ITC -> since 1 March 2007 Fondazione Bruno Kessler
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