[postgis-users] Question on transform.

[Luís Mota]

Hi Frank.

Thanks a lot for the clarification. This way I already know what to count
on...

I suppose that adding sth lihe primemer=9.23 to the proj4text won't change
anything, right?

Bye and thanks, Luís
----- Original Message -----
From: "Frank Warmerdam" <warmerdam at pobox.com>
To: <postgis-users at postgis.refractions.net>
Sent: Thursday, October 03, 2002 5:05 AM
Subject: Re: [postgis-users] Question on transform.


> Luis Mota wrote:
> > Hi everyone.
> >
> > I've been using the transform function, but I have some surprising
> > results...
> >
> > For instance, if I issue the following query:
> >
> > select transform(geomfromtext('POINT(0 38)',4803),4326);
> >
> > the result I get is:
> >       transform      -----------------------
> > SRID=4326;POINT(38 0)
> > (1 row)
> >
> > ie, exacly the same point... This is obviously wrong, since the two
> > GEOGCS's are different. For instance, the prime meridian is different..
> >
> > Is it possible that I have some instalation problem? Was this a bug
> > corrected in a later version?
>
> Luis,
>
> Note that PROJ.4 does not generally have good prime meridian support at
this
> time.  Sometimes this can be faked by using altered central merdians (for
> applicable projected coordinate systems) but the geographic/geodetic
> mechanism (+proj=latlong) does not support a prime meridian at this time.
>
> I see in the PostGIS spatial_ref_sys.sql that the PROJ.4 definition for
> 4803 is just '+proj=longlat +ellps=intl' while the more correct WKT shows
> that it should have a lisbon prime meridian.
>
> In short, I don't think you can operate on coordinate systems with
> non-greenwich prime meridians properly at this time.
>
> The following bugzilla enhancement request addresses this issue:
>
>    http://bugzilla.remotesensing.org/show_bug.cgi?id=186
>
> There is no schedule for which prime meridian support will be implemented.
> Once that is done appropriate updates to the PostGIS spatial_ref_sys.sql
> will be required.
>
> 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
>
>
>
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