[mapserver-users] Google Mercator and +nadgrids=@null

[Rahkonen Jukka]

Hi,

I saw from the thread that they are not the same. This is sad because I
have seen during just a few last days on various mailing lists and
forums that many people are now using and advising others to use the
strings from Spatialreference.org.  If I understood right, this will
lead to large offset. 

-Jukka-
 
GTsui Gerry wrote:

 
> in case you didn't see this Frank Warmerdam already addressed 
> this here:
> 
> http://n2.nabble.com/Difference-between-nadgrids-null-and-towg
> s84-0-0-0-
> td4543036.html
> 
> -----Original Message-----
> From: mapserver-users-bounces at lists.osgeo.org
> [mailto:mapserver-users-bounces at lists.osgeo.org] On Behalf Of Rahkonen
> Jukka
> Sent: Thursday, March 18, 2010 5:27 AM
> To: mapserver-users at lists.osgeo.org
> Subject: [mapserver-users] Google Mercator and +nadgrids=@null
> 
> Hi,
> 
> I have in my epsg file the following line for Google Mercator
> projection:
> 
> <900913> +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
> 
> I have copied the definitions from somewhere, I do not remember where.
> Now I noticed that http://spatialreference.org/ref/epsg/3785/proj4/
> gives this proj4 string:
> 
> +proj=merc +lon_0=0 +k=1 +x_0=0 +y_0=0 +a=6378137 +b=6378137
> +towgs84=0,0,0,0,0,0,0 +units=m +no_defs 
> 
> There seems to be one difference: my line has +nadgrids=@null 
> while the
> Spatialreference one has +towgs84=0,0,0,0,0,0,0 instead. Do they mean
> just the same thing?
> 
> -Jukka Rahkonen-
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