PHP Map projections

Question

I have Googled myself to death.. I am attempting to write 2 php functions that will return X and Y from Lat and Long, in both Mercator and flat non-projected (grid) maps. Pr

Answer 1

This presumes your lat/long coords are decimal values, and don't change direction from north/south or east/west within the visible range of the map. If they do, such values should be kept to a single format, and made negativel (eg: 1.0 S would become -1.0 N)

First you'd set the following variables, either finding them with PHP or if you know them already in the script:

$width=//width of image
$height=//height of image

$long_at_left=//Longitude of left-hand coordinates
$long_at_right=//Longitude of right-hand coordinates
$lat_at_left=//Latitude of left-hand coordinates
$lat_at_right=//Latitude of right-hand coordinates

$target_long=//Longitude you want to find
$target_lat=//Latitude you want to find

Then use:

$xtarget=$target_long-$long_at_left;
$ytarget=$target_lat-$lat_at_top;

$xdist=$long_at_left-$long_at_right;
$ydist=$lat_at_top-$lat_at_bottom;

$x=round(($xtarget/$xdist)*$width); //Percentage of distance times width
$y=round(($ytarget/$ydist)*$height); //Percentage of distance times height

Or something of that form should do the trick.