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

[Michael Barton]

On Jul 20, 2009, at 10:35 PM, grass-user-request at lists.osgeo.org wrote:

> Date: Mon, 20 Jul 2009 20:50:57 +0200
> From: Markus Neteler <neteler at osgeo.org>
> Subject: Re: [GRASS-user] m.proj transformation to EPSG3785 / KML
> To: Hamish <hamish_b at yahoo.com>
> Cc: grass-user at lists.osgeo.org, peter.loewe at gmx.de
> Message-ID:
>        <86782b610907201150v12dc3810w3ce6b43cee5bcdc5 at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> On Mon, Jul 20, 2009 at 8:16 PM, Hamish<hamish_b at 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