[postgis-users] degree vs. metric projection performance?

[Obe, Regina]

Its not in there.  The closest in there is SRID=3395 which is just
mercator.

+proj=merc +lon_0=0 +k=1.000000 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84
+units=m +no_defs

I'm not clear the differences.

I suppose we should add it since for example looking at the OpenLayers
list -  a lot of people use it
and it seems to be a defacto id if not an official EPSG code.  though
whether to use 900913 or 3785.  Neither of which are in the
spatial_ref_sys to my knowledge.

I think Google Mercator does go by multiple SRIDs, so maybe its not
really in the standard yet.  I'm actually not quite sure about that.

Here are a couple of threads
http://crschmidt.net/blog/243/google-projection-900913/

http://lists.gpsdrivers.org/pipermail/gpsdrive/2008-March/000855.html

According to this the agreed standard is EPSG:3785 but never heard of
anyone using that SRID.  Most
of the examples I have seen use 900913 so maybe the new 3785 is to cover
both Virtual Earth and Google but not sure if that quite describes both
to the letter.

http://www.sharpgis.net/post/2008/05/SphericalWeb-Mercator-EPSG-code-378
5.aspx


Hope that helps,
Regina

-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of
Pedro Doria Meunier
Sent: Wednesday, November 26, 2008 9:11 AM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] degree vs. metric projection performance?

Hi Regina :)

Could you please provide the entry for the spatial_ref_sys table for 
this SRID ?

Best regards,
Pedro Doria Meunier

Obe, Regina wrote:
>>  By the way, are the Google Mercator and WGS84 systems equivalent
>>     
>
> No they aren't.  I think Google is a mercator meter projection (not
good
> for measurement though but more or less good for presentation) and
they
> use WGS84 datum when accepting data.  I think it actually has an
> official SRID (could be wrong)
> that is EPSG:900913
>
> and proj4 looks like this
>
> +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0
+y_0=0
> +k=1.0 +units=m +nadgrids=@null +no_defs
>
> People usually plot WGS84 longlat (4326) on Google Maps, thus the
> confusion.
>
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