Projection trouble

[Bart van den Eijnden]

Hi Arnulf,

just checking a thing which maybe could cause displacement.

Does your Mapbender client use the exact same ratio of pixel coordinates
(width versus height) to world coordinates (maxx-minx versus maxy-miny).
Ofcourse there were changes in Mapserver WMS between 4.0.1 and 4.4.1 which
can cause non square pixels if the ratio differs, which maybe could cause
this ....

Just a thought.

Best regards,
Bart

On Sun, 2 Jan 2005 13:17:03 +0100, Arnulf Christl
<arnulf.christl at CCGIS.DE> wrote:

> Hi,
> sorry I postet a wrong link. The problem can be seen here:
> http://www.mapbender.org/testbed.html
> I just added a box where the projection can be changed on the fly. Zoom
> in to below 1:50000 and switch to WGS84 and everything looks fine, the
> geometries from both servers overlap perfectly. Switch to GK3
> (EPSG:31467) and there is that offset.
>
> Arnulf.
>
> Arnulf Christl wrote:
>> Hi,
>> we experience a strange offset when overlaying the same data as WMS maps
>> with MapServer versions 4.0.1 and 4.4.1.
>>
>> *4.0.1 server*
>> Windows 2000: SP4
>> IIS: 5
>> proj: came with 4.0.1
>> gd: came with 4.0.1
>> gdal: came with 4.0.1
>> Cap URL:
>> http://wms.ccgis.de/umn/bin/mapserv.exe?map=d:/umn/germany.map&SERVICE=WMS&REQUEST=GetCapabilities&VERSION=1.1.0
>>
>> Data: local shape files in EPSG:4326 projected to EPSG:31467
>>
>> *4.4.1 server*
>> FreeBSD: 4.10
>> Apache: 1.3.33
>> proj: 4.4.9
>> gd: 2.0.33
>> gdal: 1.2.1
>> Cap URL:
>> http://wms1.ccgis.de/cgi-bin/mapserv?map=/data/umn/germany_demo/germany_demo.map&VERSION=1.1.1&REQUEST=GetCapabilities&SERVICE=WMS
>>
>> Data: the same shape files as above (WGS84) but dumped to
>> PostgreSQL/PostGIS (and also projected to EPSG:31467).
>>
>> The problem does not seem to result from MapServer but from proj?
>>
>> You can have a look at the problem here:
>> http://www.mapbender.org/demoserver.html
>>
>> Zoom in to a scale of 1:100,000 or less to see the post code areas. They
>> overlap with an x-offset (north):
>> in northern Germany 190m
>> in central Germany 145m
>> in southern Germany 100m
>>
>> The y-offset (east) is:
>> in western Germany 45m
>> in eastern Germany 125m
>>
>> That resembles a lot to a datum shift which we stumbled accross (years
>> ago) when reading GPS EPSG:4326 WGS84 data directly into the database
>> and overlaying it with Gauss-Kruger EPSG:31467 (Bessel projection).
>>
>> What has been changed and what impact does it have on projects which
>> overlay other data?
>>
>> Best regards, Arnulf.
>>
>



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