I have a project using various members of Wikipedia's grey maps: http://en.wikipedia.org/wiki/Wikipedia:Blank_maps. I fill them in with colors depending on which countries, states or provinces a user selects by clicking on the shape or by checking a checkbox.
I would like to write a script that creates imagemaps automatically of each country, state or province by somehow getting the X and Y pixel location of the borders of a country, state or province albeit without the names of these entities, which I will fill in later. I have already done the World map by hand and found a open source US map image map demo. I would now like to create my maps more rapidly.
I use PHP and GD to floodfill the shapes, so I guess I could use one central pixel location of the shapes as well. Any suggestions? This script is a possibility but is still somewhat manual: http://abhinavsingh.com/blog/2009/03/using-image-maps-in-javascript-a-demo-application/. Also Mapedit, http://www.boutell.com/mapedit/, has a magic wand feature that works pretty well, but again I have a feeling this can be done automatically.
I see I can use GD PHP's imagecolorat and cycle through all the pixels to find those that are black. This works:
<?php
$im = ImageCreateFromPNG("india.png");
$width = imagesx($im);
$height = imagesy($im);
for ($cy=0;$cy<$height;$cy++) {
echo '<p>';
for ($cx=0;$cx<$width;$cx++) {
$rgb = ImageColorAt($im, $cx, $cy);
$col = imagecolorsforindex($im, $rgb);
if ($col["red"] == 0 && $col["green"] == 0 && $col["blue"] ==0){
echo $cx.", ".$cy." ";
} else {echo "";}
}
}
?>
Can anybody suggest how to find the polygons in the huge multipolygon complex that results from running the above code on say a black and white 2 color map of India, where all the borders are black and the interior of the states and Indian Ocean is white??
Here is image of India: http://wherehaveibeen.info/images/india.png and the mess now of the coordinates for the imagemap that needs to be split up into separate polygons: http://wherehaveibeen.info/images/black.php
