Opened 15 years ago
Closed 15 years ago
#42 closed defect (fixed)
No support for the Google Mercator projection.
| Reported by: | Norm Olsen | Owned by: | hugueswski |
|---|---|---|---|
| Priority: | major | Milestone: | 2.0 |
| Component: | Library | Version: | svn-trunk |
| Keywords: | Mercator Google | Cc: |
Description
The CS-MAP implementation does not support explicitly the Google Mercator projection; named Popular Visulation Mercator by EPSG.
The Google Mercator uses the spherical formulation of the standard Mercator projection even though the CRS definition teferences a datum, and therefore an ellipsoid. Thus, a CRS directly referenced to a "spherical ellipsoid" would do the trick, but this disables all datum shifts.
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Corrected at revision # 1619.
The submission which addressed this issue added three new projection vairations.
* Popular Visualization Pseudo Mercator -- This variation uses the spherical formulation of the standard Mercator projection even if the CRS is referenced to an ellipsoid (usually through a datum reference). Thus, the projection calculations match those of Google Maps and Microsoft Virtual Earth without disabling datum shift calculations where appropriate. The new projection key name is MRCAT-PV, the projection code is 69, and the name is "Popular Visualisation Pseudo Mercator"; name and spelling chosen to match EPSG.
* Ellipsoidal form of the Equidistant Cylindrical -- CsMap has always supported the spherical form of this projection, but not the ellipsoidal form. To properly implement the Plate Carree (next described), it was appropriate to implement the ellipsoidal form of the the Equidistant Cylindrical (formulation obtained from EPSG Guidance Note 7.2). To ensure no regressions, this has been implemented as a complete new projection with key name "EDCYL-E", projection code 67, and name of "Equidistant Cylindrical Projection (Ellipsoidal or Spherical)". The older implementation has been marked as "Deprecated" but remains fully supported. * Plate Carree -- This is a rigorous implementation of the Plate Carree projection. It is _NOT_ the pseudo Plate Carree as implemented by EPSG (that remains another project). The key name is "PCARREE", projection code is 68, and the projection name is "Plate Carree / Simple Cylindrical". The projection name is of French origin and the first 'e' in Caree should have an accent; this was not attempted in the code.
The Plate Carree implementation was intended to enable proper coordinate system assignment for raster images which are images of maps rendered using, for example, "LL84". This is a problematical situation as the raster images whould often exceed the traditional boundas for latitude and lonitude, producing undesirable side affects when LL84 is used.