problem with Mapserver WCS handling of NaN?

[Frank Warmerdam]

Jeff de La Beaujardiere wrote:
> The Web Coverage Service (WCS) feature is (sort of) working
> on our installation, now that our sysadmin recompiled --with-wcs.
> 
> However, the not-a-number (NaN) values in the floating-point GeoTIFF
> data files used as input do not seem to be handled correctly.
> 
> - When the GeoTIFF is a single global dataset, the NaNs are converted
> to zeroes. I can filter those out of these particular data only
> because the valid data are all in a range > 0.
> 
> - More seriously, when there are multiple GeoTIFF files enumerated
> in a tile index, the NaN areas overwrite data from earlier GeoTIFFs,
> even though the WMS component handles this properly. For example,
> this test image was generated via WMS:
> http://www.map.nasa.gov/test/soar/wms-nans.png
> The no-data areas are blank and transparent, as desired
> (the black rectangle has something to do with my attempt to classify
> the raster data, but is a different problem than the NaN problem).
> This test image was generated from the WCS output:
> http://www.map.nasa.gov/test/soar/wcs-nans.png
> The no-data areas are opaque zeroes that hide valid data
> from other granules.

Jeff,

GDAL does not generally support specifying NaN as a nodata value,
and neither does MapServer specifically support this.   If you wanted,
we could look at mechanisms to specify NaN as a nodata value in GDAL
but even at that I'm not positive that the case you are using for WCS
in MapServer even honours nodata values in the source data.

Is it practical for you to work with files with a more conventional
style of data value?  If not, perhaps we should follow up on this
by private email.

Best regards,
-- 
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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    | President OSGeo, http://osgeo.org