[gdal-dev] Re:

[Jason Roberts]

Riki,

Please let us know whether Frank's suggestion works or not. I have been
experimenting with writing GeoTIFFs using GDAL 1.6.0 and the Python bindings
and have not been successful so far at using GDAL to calculate statistics
that ArcGIS recognizes. It would be interesting to know whether this
suggestion will work.

If anyone is interested, after creating a GTiff with one band, writing
values to the band, flushing the cache, I have been calling

    band.SetStatistics(*band.GetStatistics(False, True))

and then looking at the resulting file from ArcGIS 9.3.1 (the latest
version). ArcGIS reports that there are no statistics. I can then calculate
them with ArcGIS, if desired, but like Riki, it would be useful if I did not
need to do this.

The technique works for .img files (HFA driver). If I do not call
SetStatistics, ArcGIS reports there are no statistics. But when I do call
it, as shown above, ArcGIS can see the statistics. This led me to believe it
was the right technique but that there is a GDAL/ArcGIS incompatibility
around statistics in GeoTIFFs.

Another thing that ArcGIS users should be aware of is the that the Calculate
Statistics tool in ArcGIS also creates a raster attribute table. GDAL
SetStatistics does not do this. GDAL 1.6.x appears to have some
functionality relating to raster attribute tables but I have not
experimented with it yet. It is another thing to check for if you're looking
for 100% compatibility between GDAL and ArcGIS.

Finally, I am encountering an issue with NoData values. Riki can you please
let us know if NoData cells show up properly in ArcGIS? When I call
band.SetNoDataValue when creating a GTiff with the Python API, ArcGIS does
not seem to recognize it. I also tried CreateMaskBand() with
GDAL_TIFF_INTERNAL_MASK set to YES. It did not work either.

Best regards,

Jason

-----Original Message-----
From: gdal-dev-bounces at lists.osgeo.org
[mailto:gdal-dev-bounces at lists.osgeo.org] On Behalf Of Frank Warmerdam
Sent: Thursday, September 17, 2009 2:05 PM
To: Riki Tiki
Cc: gdal-dev at lists.osgeo.org
Subject: [gdal-dev] Re:

Riki Tiki wrote:
> @Frank and Hermann: Thanks a lot!
> 
> My other question is as follows:
> 
> 1) gdal_translate -of AAIGrid a.tif a.asc
> 
> it creates the following: a.asc (ASC File), a.asc.aux (XML Document), and
a
> (IDL project file)...

Riki,

Not that the .prj file is not an IDL project file, it is an ArcGIS
projection file.

> now to do the reverse i do the following:
> 
> 2) gdal_translate -of GTiff a.asc a.tif
> 
> it creates: a.tif (TIF Image)
> 
> but when i open a.tif with ArcGIS it shows that its statistics are not
> calculated...
> 
> Can you tell me how to create the 2) with statistics already computed? So
> that when i open it in ArcGis for example I do not have to ask ArcGIS to
> compute the statistics? Thanks a lot!

If you use a recent enough version of ArcGIS the following *might*
precompute the stats in a useful fashion for ArcGIS.

   gdalinfo -stats a.tif

Best regards,

-- 
---------------------------------------+------------------------------------
--
I set the clouds in motion - turn up   | Frank Warmerdam,
warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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