[gdal-dev] Re: gdal_translate -unscale option

[jt2000]

Frank,

Does the unscale option work as advertised?

I have a raster with offset and scale set.

Driver: GTiff/GeoTIFF
Files: raster.tif
       raster.tif.aux.xml
Size is 10295, 7735
Coordinate System is:
PROJCS["unnamed",
    GEOGCS["unnamed",
        DATUM["North_American_Datum_1983",
            SPHEROID["GRS 80",6378137,298.257222101],
            TOWGS84[0,0,0,-0,-0,-0,0]],
        PRIMEM["Greenwich",0],
        UNIT["degree",0.0174532925199433]],
    PROJECTION["Transverse_Mercator"],
    PARAMETER["latitude_of_origin",0],
    PARAMETER["central_meridian",-87],
    PARAMETER["scale_factor",0.9996],
    PARAMETER["false_easting",500000],
    PARAMETER["false_northing",0],
    UNIT["Meter",1]]
Origin = (246885.000000000000000,4726455.000000000000000)
Pixel Size = (30.000000000000000,-30.000000000000000)
Image Structure Metadata:
  INTERLEAVE=BAND
Corner Coordinates:
Upper Left  (  246885.000, 4726455.000) ( 90d 5'15.87"W, 42d38'56.20"N)
Lower Left  (  246885.000, 4494405.000) ( 89d59'22.95"W, 40d33'42.29"N)
Upper Right (  555735.000, 4726455.000) ( 86d19'10.68"W, 42d41'18.81"N)
Lower Right (  555735.000, 4494405.000) ( 86d20'28.58"W, 40d35'54.87"N)
Center      (  401310.000, 4610430.000) ( 88d11' 5.93"W, 41d38'22.21"N)
Band 1 Block=10295x1 Type=Float32, ColorInterp=Gray
*  NoData Value=0
  Offset: -200,   Scale:0.00305185094759972*


when I do a gdallocationinfo on it, i get the value of -90.82 as follows:

gdallocationinfo -b 1  raster.tif 3000 3342
Report:
  Location: (3000P,3342L)
  Band 1:
    Value: -90.8230819702148
    Descaled Value: -200.277178508775

Applying unscale
 gdal_translate -unscale -of GTiff ~/raster.tif raster2.tif

 gdallocationinfo -b 1  raster2.tif 3000 3342                                    
Report:
  Location: (3000P,3342L)
  Band 1:
    Value: -200.27717590332

I would have expected -90.82 as the value.  Am I wrong?

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