[Proj] Proj Digest, Vol 58, Issue 10

[Stephan Holl]

Hello Richard,

proj-request at lists.maptools.org, [20090311 - 12:00:02]

> Date: Wed, 11 Mar 2009 06:34:19 -0600
> From: Richard Greenwood <richard.greenwood at gmail.com>
> Subject: Re: [Proj] Errors between proj 4.5 and 4.6.1 with epsg:31467
> To: "PROJ.4 and general Projections Discussions"
> 	<proj at lists.maptools.org>
> Message-ID:
> 	<ae9185aa0903110534lef72ea1n6ccd516277a78497 at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
> 
> On Wed, Mar 11, 2009 at 4:07 AM, Stephan Holl
> <stephan.holl at intevation.de> wrote:
> > Dear proj-users,
> >
> > a customer has updated a test-server from proj 4.5.0 to 4.6.1
> > linked to a PostGIS-DB and a UMN MapServer with a WMS on top.
> >
> > The result of the identical WMS-request on a server working with
> > proj 4.5.0 and 4.6.1 have different results in their accurancy,
> > about a 100m north-shift.
> >
> > Did anybody came accross this problem?
> >
> > I tried to scan the ChangeLog of 4.6.1 but did not find any relevant
> > entries which might be the cause of this change.
> >
> > TIA.
> 
> Stephan,
> 
> >From PROJ 4.6.0 on datum shifts are only applied if datum
> >information  
> for both the source and destination coordinate systems is defined.
> EPSG:31467 defines a datum. I am guessing that is the coordinate
> system of your source data. Do you know what coordinate system the WMS
> request is asking for, and does that coordinate system have a datum
> defined, or twgs84 parameters?

Thanks for your quick answer. This is good news, but I am not quite
sure which values to add so that the results will be identical of the
proj 4.5.0-version.

I do have a source-projection of epsg:25832 which is defined (in both
pproj4.5.0 and 4.6.1) as
# ETRS89 / UTM zone 32N
<25832> +proj=utm +zone=32 +ellps=GRS80 +units=m +no_defs  <>

So towgs84 is missing here and I have to add this here in my MapFile?

So adding a +datum=wgs84 will suffice?

TIA

	Stephan

-- 
Stephan Holl <stephan.holl at intevation.de> | Tel.: +49 (0)541-33 508 3663
Intevation GmbH, Neuer Graben 17, 49074 OS  |  AG Osnabrück - HR B 18998
Geschäftsführer:  Frank Koormann, Bernhard Reiter, Dr. Jan-Oliver Wagner
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