[Proj] Algorithms & Plate Carrée

Irwin Scollar al001 at uni-koeln.de
Mon Jul 23 11:47:02 EST 2012

Noel Zinn wrote:

"Where does Plate Carree figure into this?  Not from Google Earth where the
poles can be displayed, not possible in Plate Carree.  I'd guess that the
"projection" you get in Google Earth is an ellipsoidal orthographic, ..."

That applies at the Poles, but:

The Google Earth help page says:

Google Earth uses Simple Cylindrical projection with a WGS84 datum 
for its imagery base. Simple Cylindrical (Plate Carree) Projection 
and displays an image of it.  See:


Hopefully, given some of the sources of distortion in a GE image, a 
correction solution may be fairly simple within the limits of the 
resolution of the imagery..

By small area, I mean something between 1 and 4 km square. Polar 
areas are of no interest for my application.  Only those areas with 
high resolution imagery are of concern. By this I mean the products 
which Google buys in the form of geometrically corrected orthophotos 
from national e.g. IGN-France or local mapping services, e.g. 
Germany, in those parts of the world where they expect that 
advertising revenue will accrue,  or where they get good quality 
imagery from their leased GeoEye now merged with Digital Globe which 
can be used in much of North Africa and the Middle and Far East.

20-30 cm per pixel is available and in a very few instances, ca.10-15 
cm (Netherlands), but 50 cm. per pixel is about average for built-up 
areas in Europe and the Middle East.  In some cases, Google has 
obtained their data from national or local GeoPortal sites whose 
imagery has been placed on the Web under the European Union Inspire directive.

It's usually easier to search with Google Earth or even with Bing 
Maps which sometimes has better material if Microsoft's own aircraft 
has been making the pictures using their Austrian subsidiary's Vexcel 
mapping cameras.  GeoPortals do not have uniform user interfaces or 
languages and quality varies widely.  Google is the only supplier of 
fairly decent data over much of the world, hence my interest.


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