[Proj] Common term for geographic and projected coordinates?

Eric Miller EMiller at dfg.ca.gov
Wed Feb 4 14:43:46 EST 2009

>>> On 2/4/2009 at 10:37 AM, "Karney, Charles" <ckarney at Sarnoff.com>
>>  From: Mikael Rittri [Mikael.Rittri at carmenta.com] 
>> Date: Wednesday, February 04, 2009 05:19
>> Subject: [Proj] Common term for geographic and projected
>>    I am trying to document a method that tranforms pixel
>> to either projected or geographic coordinates, depending on whether
>> the window is presented with a map projection or just as lat-lon
>> right, Pseudo Plate Carrée).
> In the vision world, the conversion for "world" coordinates to pixels
> accomplished by a "camera matrix"
>     http://en.wikipedia.org/wiki/Camera_matrix 
> In general this is a projective map from 3d to 2d.  The simple case
> you're considering is a similarity transform.  The transformation
> pixel to projected coordinates is given by the inverse of the camera
> matrix.

I don't think that's what the op is interested in.  It's just 2D to 2D
scaling and translation with some type conversion handling (int <->
double).  I couldn't find a good explanation online but search for
"converting screen coordinates to map coordinates" or something similar.
 The map coordinates are always some projection as the op noticed.  It's
basic algebra/geometry. 


Eric G. Miller
Staff Programmer
CA Dept. of Fish & Game

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