[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>
wrote:
>> From: Mikael Rittri [Mikael.Rittri at carmenta.com]
>> Date: Wednesday, February 04, 2009 05:19
>> Subject: [Proj] Common term for geographic and projected
coordinates?
>>
>> I am trying to document a method that tranforms pixel
coordinates
>> to either projected or geographic coordinates, depending on whether
>> the window is presented with a map projection or just as lat-lon
(all
>> right, Pseudo Plate Carrée).
>
> In the vision world, the conversion for "world" coordinates to pixels
is
> 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
from
> 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
More information about the Proj
mailing list