[Gdal-dev] negative nodata value loaded as positive in gdal 1.4.0

[Hernán De Angelis]

Maciek,

> FWIW, this is not correct. r.in.srtm is a script which uses r.in.gdal,
> not gdal_translate.
Thanks for responding and thanks for pointing out this mistake.

Today I tried a large number of SRTM tiles, including 1" and 3" as well as  
versions 1 and 2 and the problem is still present, so I also came to the 
conclusion that it is likely a bug in GDAL. I hope some one else can comfirm 
this.

Thanks

Hernán


> However, both r.in.gdal and gdal_translate have the problem Hernán
> describes, so propapably this is an issue with GDAL itself; unless an
> issue with some problematic SRTM tiles, ?. I'm not up to tracing it
> down exactly, but anybody who can please read below.

> > nodata values are loaded
> > as 32768 (positive) even when -32768 is explicitly set in the script.
> > After import gdalinfo reports nodata as -32768, but r.info (in GRASS),
> > cmm (in OSSIM) and OpeneEV all report these cells as 32768 (positive). I
> > am using gdal 1.4.0. Is anyone else having this problem as well?
>
> I confirm. I can reproduce this with some 3" tiles, eg:
> ftp://e0srp01u.ecs.nasa.gov/srtm/version2/SRTM3/Eurasia/N49E023.hgt.zip
>
> I checked whether this is related to the SRTM version - it's not; same
> problem with the version 1 at:
> ftp://e0srp01u.ecs.nasa.gov/srtm/version1/Eurasia/N49E023.hgt.zip
>
> After importing the tile into GRASS with r.in.srtm (ie. r.in.gdal), the
> max value of the output raster is 32768 - wrong. Should be circa 1200.
> Min is OK - 153.
>
> I have also checked with gdal_translate, and the same issue remains.
> The value range is reported as 153-32768, see:
>
> $ gdalinfo N49E023.bil -mm
> Driver: EHdr/ESRI .hdr Labelled
> Size is 1201, 1201
> Coordinate System is `'
> Origin = (22.999583333333334,50.000416666666666)
> Pixel Size = (0.000833333333333,-0.000833333333333)
> Corner Coordinates:
> Upper Left  (  22.9995833,  50.0004167)
> Lower Left  (  22.9995833,  48.9995833)
> Upper Right (  24.0004167,  50.0004167)
> Lower Right (  24.0004167,  48.9995833)
> Center      (  23.5000000,  49.5000000)
> Band 1 Block=1201x1 Type=UInt16, ColorInterp=Undefined
>     Computed Min/Max=153.000,32768.000
>   NoData Value=-32768
>
> I have put the problematic SRTM V2 tile N49E023 (converted into
> bil+hdr) for download here:
>
> http://kufaya.googlepages.com/srtm_v2_N49E023_bil_hdr.tar.bz2
>
> Using GDAL 1.4 CVS 2007-01-14 (today).
>
> Maciek

-- 
Hernán De Angelis
Linux user # 397217