Articles Tricks And Hacks
Tricks And Hacks
GIS Mapping with PHP - Page 3
by: Simon Moss
|
October 23, 2003
Plots and Schemes
The basic steps for generating the map are:
- Load the background map.
- Convert and scale the long/lat coordinates to screen coordinates.
- Plot the point.
- Return the finished map as an image.
To convert the long/lat to screen coordinate we have a created a function called
getlocationcoords. This takes the longitude and latitude coordinates
plus the size of the base map and return the screen coordinates in an associative
array. $width and $height are calculated from the
size of the background image. In future projects these variables are used scale
the map and set the zoom level.
<?php
function getlocationcoords($lat, $lon, $width, $height)
{
$x = (($lon + 180) * ($width / 360));
$y = ((($lat * -1) + 90) * ($height / 180));
return array("x"=>round($x),"y"=>round($y));
}
?>
Once the coordinates have been converted it's as simple as drawing a rectangle
on the base map using the returned array to mark our location.
