[Mapserver-users] Geting Image X and Y for dynamically-added points

[Erich Schroeder]

Chip,
  Thanks, now that you point it out I remember having this shown to me at 
MUM. I'll work on this tonight.

Erich

On Tue, 16 Sep 2003, Chip Hankley wrote:

> Erich -
> 
> You just need to work backwards. You will know the extent of your image
> in real coordinates, and the size of your image in pixels. Once you know
> these, it's pretty straightforward to solve for the pixel coordinates:
> 
> ImgX = ((MapX - MapMinX)/(MapMaxX - MapMinX)) * ImgWidth
> 
> The components of this are:
> ((MapX - MapMinX)/(MapMaxX - MapMinX)) gives you the % in the X
> direction, multiplied by the ImgWidth gives you the pixel number
> 
> so if you're point is located 50% along the current mapextent, and your
> image is 500 pixels wide, the ImgX location will be 0.5 * 500 = 250.
> 
> Do a similar thing for ImgY, but remember that ImgY STARTS at the top
> and increases down.
> 
> Chip
> 
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Erich Schroeder                    Phone: (217)785-0033
Curator, Information Technologies  FAX:   (217)785-2857
Illinois State Museum GIS Lab      email:erich(at)illinois.state.museum
                 http://illinois.state.museum/
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