On Jul 20, 2009, at 10:35 PM, grass-user-request@lists.osgeo.org wrote:
Date: Mon, 20 Jul 2009 20:50:57 +0200
From: Markus Neteler <neteler@osgeo.org>
Subject: Re: [GRASS-user] m.proj transformation to EPSG3785 / KML
To: Hamish <hamish_b@yahoo.com>
Cc: grass-user@lists.osgeo.org, peter.loewe@gmx.de
Message-ID:
<86782b610907201150v12dc3810w3ce6b43cee5bcdc5@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1On 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
Yes. But using wgs84 LL for Google Earth data also produces errors of up to a couple hundred meters...in GRASS. One of my students is trying to deal with this.
Michael