[GRASS-user] m.proj transformation to EPSG3785 / KML

GRASS GRASS user
1

Hi,

how can m.proj (being the frontend to cs2cs) be configured to create output in the "Google projection" (aka EPSG 900913 / EPSG 3785) ?

These EPSG codes are currently not included in /usr/share/proj/epsg.

Peter
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2

Hi Peter,

how can m.proj (being the frontend to cs2cs) be configured
to create output in the "Google projection" (aka EPSG 900913
/ EPSG 3785) ?

just use the expanded version as proj_out proj4 terms.

These EPSG codes are currently not included in
/usr/share/proj/epsg.

they can be found in /usr/share/proj/esri.extra

FWIW & AFAIK, KML takes coordinates as wgs84 LL, and the "Google
projection" is a highly dubious beast that should be avoided if
at all possible.

Hamish

3

On Mon, Jul 20, 2009 at 8:16 PM, Hamish<hamish_b@yahoo.com> wrote:
...

FWIW & AFAIK, KML takes coordinates as wgs84 LL, and the "Google
projection" is a highly dubious beast that should be avoided if
at all possible.

Yes!
See also comment here:
http://www.epsg-registry.org/export.htm?gml=urn:ogc:def:crs:EPSG::3857
"<remarks>
Uses spherical development of ellipsoidal coordinates. Relative to an
ellipsoidal development errors of up to 800 metres in position and 0.7
percent in scale may arise. It is not a recognised geodetic system:
see WGS 84 / World Mercator (CRS code 3395).
</remarks>
"

The error is significant for many GIS applications.

Markus

4

Hi Markus, hi Hamish,

thank you for your feedback and advice. The 900913-projection is a "strange beast", indeed. But it's good that GRASS allows to communicate with communities which willfully avoid everything else.

Peter

-------- Original-Nachricht --------

Datum: Mon, 20 Jul 2009 20:50:57 +0200
Von: Markus Neteler <neteler@osgeo.org>
An: Hamish <hamish_b@yahoo.com>
CC: grass-user@lists.osgeo.org, peter.loewe@gmx.de
Betreff: Re: [GRASS-user] m.proj transformation to EPSG3785 / KML

On Mon, Jul 20, 2009 at 8:16 PM, Hamish<hamish_b@yahoo.com> wrote:
...
> FWIW & AFAIK, KML takes coordinates as wgs84 LL, and the "Google
> projection" is a highly dubious beast that should be avoided if
> at all possible.

Yes!
See also comment here:
http://www.epsg-registry.org/export.htm?gml=urn:ogc:def:crs:EPSG::3857
"<remarks>
Uses spherical development of ellipsoidal coordinates. Relative to an
ellipsoidal development errors of up to 800 metres in position and 0.7
percent in scale may arise. It is not a recognised geodetic system:
see WGS 84 / World Mercator (CRS code 3395).
</remarks>
"

The error is significant for many GIS applications.

Markus

--
Dr. Peter Löwe
<peter.loewe@gmx.de>

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