[OSGeo-Discuss] WCS/WMS accuracy tests?

Stephen Woodbridge woodbri at swoodbridge.com
Mon Dec 7 08:47:08 PST 2009

Steven M. Ottens wrote:
> Hi all,
> Working with Geoserver as a WCS we discovered that requesting a
> GeoTIFF in the same projection as the original GeoTIFF produces a
> shifted dataset. (http://jira.codehaus.org/browse/GEOS-3702) The
> shift is small, less than one pixel of the original dataset, but with
> a coarse dataset of 100m/pixel it can be 70meters. The Geoserver
> people are aware of the problem and at some point in time will fix it
> I'm sure, but it prompted me to test other OSS WCS servers (mapserver
> and deegree). Both of them showed a shift of the data as well. 
> Deegree has about the same error as Geoserver, while Mapserver does a
> better job but is still off.
> I know there have been speed tests between different WMS services,
> but I'm wondering has there been any data-quality/accuracy test been
> done between WMS and/or WCS services?

I wonder if this is the difference between pixel as a point versus pixel 
as an area. Mapserver uses gdal to handle GeoTiff files and Frank has 
put a lot of effort in Gdal to handle this correctly.

Also, I'm surprised that there is any shift in mapserver because I do 
not think mapserver reprojects data if the in and out projections are 
the same. I can speak for the other services as I don't know how they work.

-Steve W

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