# [mapserver-users] Convert Geo Points to Image Points

Gail Long codeburg at hotmail.com
Thu Jul 17 09:11:33 EDT 2008

```I'm trying to convert a geopoint into an image coordinate so I can place images on a floating div over a map.

I know how to go from image points to geo points and figured that just reversing the process was the way to go back.  Apparently it is not.

Here is what I was trying:

<?php
\$minx_geo = 2422041.973271;
\$miny_geo = 654245.367973;
\$maxx_geo = 2565405;
\$maxy_geo = 781169.610946;

\$minx_img = 0;
\$miny_img = 0;
\$maxy_img = 200;
\$maxx_img = 300;

\$mapwidth = 300;
\$mapheight = 200;

\$xdelta_geo = \$maxx_geo - \$minx_geo;
\$ydelta_geo = \$maxy_geo - \$miny_geo;

\$xdelta_img = \$maxx_img - \$minx_img;
\$ydelta_img = \$maxy_img - \$miny_img;

\$x_pix = 150;
\$y_pix = 100;

// Calculate the image coords to map extents
\$x_geo = \$minx_geo + ((\$x_pix/\$mapwidth) * \$xdelta_geo);
\$y_geo = \$maxy_geo - ((\$y_pix/\$mapheight) * \$ydelta_geo);

// Calculate map points to image coords
\$x_img  = \$minx_img + ((\$x_geo/\$mapwidth) * \$xdelta_img);
\$y_img = \$maxy_img  - ((\$y_geo/\$mapheight) * \$ydelta_img);

print "\$x_geo \$y_geo\n";
print "\$x_img \$y_img\n";

I'm math challenged so this probably is easier than it seems but I'm not groking it.

Thanks very much for any assistance.

Gail
?>

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