[Gdal-dev] Projected vs Geographic Coordinate Systems

Simon Perkins sy at perkins.net
Tue Mar 20 00:48:09 EDT 2007

Simon Perkins wrote:
> In a related question, if I have a vector layer in a geographic 
> coordinate system, does OGR provide some convenient way to compute the 
> relative scaling of degrees in the east-west and north-south 
> directions? I guess it comes down to some simple geometry (the size of 
> latitude degrees is uniform, the size of longitude degrees go like 
> square of cosine of latitude, I think) , but just wondered if there 
> was some more sophisticated procedure for what must be a common task.

Er, I mean, longitude degrees go like the cosine of the latitude. Not 
sure where the square came from...

This is assuming a sphere of course, but as Frank says, all projections 
are lies, so this is probably good enough.



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