I've been starting to use GeoServer caching (geowebcache) more often and
have a question regarding the caching for the web mercator or Google
projection.
The "official" EPSG code for the web mercator projection is EPSG:3857.
GeoServer does support this by default. However, geowebcache uses 900913
as a default gridset. Perhaps that should be 3857?
As well, the default definition for 3857 in GeoServer is missing the datum
transformation parameters. Adding something like the following should work.
TOWGS84[0,0,0,0,0,0,0],
(In PROJ.4 format, "+nadgrids=@null" could also be added to not use any
grid shift fileand apply a zero shift.)
It was also mentioned in the article
http://alastaira.wordpress.com/2011/01/23/the-google-maps-bing-maps-spherical-mercator-projection/(good
summary), that the prpjection name should be changed to:
PROJECTION["Mercator"]
Apparently, 3857 is not in spatialreference.org but these two are very
close.
http://spatialreference.org/ref/sr-org/6864/
http://spatialreference.org/ref/sr-org/7483/
So, with all that said, my questions are:
1) Should GeoWebCache use 3857 rather than 900913 as the default web
mercator gridset?
2) Should the definitions of 3857 and/or 900913 be changed in GeoServer?
or maybe entries can be added to override these reference systems
in \geoserver_data\user_projections?
3) Would anyone recommend building cache tile sets for both 3857 and 900913
(since clients may be use either one)?
Thanks for your help/.
- John
John Callahan
Research Scientist
Delaware Geological Survey
University of Delaware
http://www.dgs.udel.edu
john.calla...@udel.edu
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