#1536: add EPSG:900913 to location wizard
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Reporter: timmie | Owner: grass-dev@…
Type: defect | Status: new
Priority: normal | Milestone: 6.4.2
Component: Projections/Datums | Version: 6.4.2 RCs
Keywords: | Platform: MSWindows XP
Cpu: Unspecified |
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The Google Mercator Projection sometimes referred to as ESRI-EPSG code
900913 while it does not have an official code? http://spatialreference.org/ref/sr-org/6/
after originally reacting with horror, AFAIU the epsg people have given up
the fight and issued the spherical mercator with wgs84's major ellipsoid
radius its own epsg code. So this will be fixed in time with a new version
of the epsg file and the only action needed is to wait. it is not
recommended to use spherical merc for real analysis, only data transfer
and matching visual cartography.
it is designed to be very fast on their servers, not to seek the ultimate
perfection in geodesy. (fair enough for their needs)
I think g.proj works but it isn't listed in the wizard as the wizard just
parses the main epsg file while g.proj uses the PROJ4 library which also
checks the esri.extra file that contains the "Chris's funny" projection.
be careful calling it the 'google' projection, their google maps slippy
tile projection is a slightly different thing again (and even more
distorted). each row of tiles has its own slightly different projection!
the two are related but get confused a lot.
#1536: add EPSG:900913 to location wizard
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Reporter: timmie | Owner: grass-dev@…
Type: enhancement | Status: new
Priority: normal | Milestone: 6.4.2
Component: Projections/Datums | Version: 6.4.2 RCs
Keywords: google projection, epsg | Platform: All
Cpu: Unspecified |
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Changes (by neteler):
* platform: MSWindows XP => All
Comment:
I would note that it is not the official code:
{{{
tail -3 /usr/share/proj/esri.extra
# Chris' funny epsgish code for the google mercator
#
<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 +wktext +no_defs <>
}}}
The fact that 900913 exists is AFAIK historically: to get +nadgrids=@null
into a code. For subsequent history, see Hamish's comment above.
The SphericalMercator projection in OpenLayers uses code epsg:900913. When
Google started to use the SphericalMercator projection, a corresponding
EPSG
code did not yet exist, so a temporary code '900913' (notice the
resemblance
to the word 'google') was invented. Many other services, such as
OpenStreetMap,
Bing and Yahoo are now also using the same projection, but are not
necessarily
supporting the use of code EPSG:900913. Other codes, such as EPSG:3857 and
EPSG:102113 were invented. Today, there is an officially registered EPSG
code
3857 whose projection is identical to EPSG:900913.
(http://www.epsg-registry.org/export.htm?gml=urn:ogc:def:crs:EPSG::3857)."
I would suggest to support the official code rather than the inofficial
one
which may disappear since superceeded.
