WCS: error on creating large Geotiff from ECW

[Frank Warmerdam]

On 1/6/06, Bart van den Eijnden <bartvde at xs4all.nl> wrote:
> Hi list,
>
> I am trying to create a Geotiff file from an ECW file using Mapserver WCS
> (Mapserver 4.8beta2, GDAL CVS 04/01/06, ECW SDK 3.3RC1).
>
> The request is:
> http://[ip]:[port]/cgi-bin/mapserv480?map=/data/OGC_UMN_services/basispakket_dkln.map&bbox=157200,456945,161080,459273&service=WCS&version=1.0.0&exceptions=application/vnd.ogc.se_xml&request=GetCoverage&coverage=AAA154&crs=epsg:28992&resx=.5&resy=.5&format=Geotiff
>
> The following error message occurs:
>
> error: could not get data:
> NCScbmReadViewLineBIL failed.: Unable to access file. GDALRasterIO()
> failed: drawGDAL()
>
> The same part of the ECW can be rendered by Mapserver WMS without
> problems. When I try a smaller WCS request, it does work.
>
> Any ideas what could be the problem and how to solve it?

Bart,

I can't think of any obvious reason this would be happening.
Especially why WCS and WMS would react differently in
this regard.

I have run into a few bugs in the last few months that relate
to unusual access patterns to the ECW SDK from GDAL.  Some
of these (or all?) all been fixed by ERMapper and should appear
in their next release.  But I don't know when that will be.

You might have some luck fiddling with the config settings
that can affect the GDAL ECW drivers low level access.
For instance, trying setting the following in your mapfile.

CONFIG "GDAL_FORCE_CACHING" "YES"

This will generally reduce MapServer performance since
the alternative (one big request to the ECW file is usually
faster than many smaller block reads for the cache), but
it might be more stable.

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