[Proj] Proj Digest, Vol 58, Issue 10

[Richard Greenwood]

On Thu, Mar 12, 2009 at 2:24 AM, Stephan Holl
<stephan.holl at intevation.de> wrote:
> 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
>

Yes, that should work. I notice that it is usually upper case:
+datum=WGS84, or adding +towgs84=0,0,0 should do the trick also.

-- 
Richard Greenwood
richard.greenwood at gmail.com
www.greenwoodmap.com