[FWTools] Gdaltranslate ESRI grid to GeoTIFF: pixel values are blown up.

[Frank Warmerdam]

Frans Knibbe wrote:
> Hello,
> 
> I am trying to prepare elevation grids for display and query with the 
> UMN MapServer. The source data are ESRI floating point grids. As I 
> understand geoTIFF to be a good format to use with MapServer I use 
> gdaltranslate (from FWTools 1.0.5) to convert the grids to geoTIFFs. The 
> problem is that in the resulting geoTIFF images the pixel values are 
> somehow blown up. Gdalinfo does not report the minimum and maximum 
> values of the GeoTIFFs, but opening a file in ArcMAP reveals the minimum 
> value to be 1.17E-38 and the maximum value to be 3.4E38, when the 
> original values were -6.96 and 30.5.
> 
> When I use ArcMap to convert the grids to TIFF, the pixel values do seem 
> correct, but somehow those TIFFs are not drawn by MapServer. MapServer 
> does draw the files made by gldaltranslate. Can anyone help me with 
> getting the pixel values right?

Frans,

If you could create a small arcinfo grid, and convert it to geotiff both
ways, and then send me the two outputs and the input all zipped up I can
try to analyse the difference.

I vaguely suspect the problem is that ArcMap isn't getting min/max metadata
value from the GDAL produced GeoTIFF and that is resulting in default
scaling.  But it is hard to be sure.

It would be best to submit this as a bug report against GDAL in the GDAL
bugzilla.

Best regards,
-- 
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