Think Blue

 

Code Tags: PHP;Mysql
I needed to plot visitors to a web site onto a world map to demonstrate world wide coverage. I had an initial google around and couldn't really find anything. It didn't take too long to realise what i needed to make this work with my own script. I also chose to make it pretty so have gone for a lights at night look.


Problem
* Put locations of visitors (for which i already had in a mysql database) on to a world map.

Pre-Requisites
* The data (this example will assume from mysql)
* A World Map (I have gone for "AVHRR Pathfinder" shot from here) the bigger the better)
* PHP with gd2 (I run this from the command line as it might take a while to render)

Understanding the Maths
Firstly to make this work you need a linear cylindrical (latitude/longitude) projection world map, the ones from the source outlined above are. This means that the latitude/longitude are directly proportional to the x/y of the image. So if you have the dimensions the image as $img_x, $img_y you can then plot a long/lat with this:

php code:
$pos_x = (int)(($img_x/2) + (($row['long']/180)*($img_x/2)));
$pos_y = (int)(($img_y/2) - (($row['lat']/90)*($img_y/2)));

For Longitude ($row['long']): the range is from -180°:180° so the above code work out the equivalent x position on the image. The same applies for Latitude($row['long']) with the range -90°:90°

With this sorted the rest of the code is simple.

The Code

php code:
//Setup Image
$imagein = "PathfinderMap.jpg";
$imageout = "output.jpg";
 
//Get Image Dimentions
list($img_x,$img_y) = getimagesize($imagein);
 
//Load in image
$im = imagecreatefromjpeg($imagein);
 
//Make Image "Night time"
$darkblue = imagecolorallocatealpha($im, 0x00, 0x00, 0x00, 25);
imagefilledrectangle($im, 0, 0, $img_x,$img_y, $darkblue);
 
//Mysql Bit
$mysqli = new mysqli("**","**","**","**");
if ($mysqli->connect_error) {
    printf("Connect failed: %sn", mysqli_connect_error());
    exit();
}
 
	$sql = "** Protected for Security **";
 
 
if ($result = $mysqli->query($sql)) {
 
    while ($row = $result->fetch_array(MYSQLI_ASSOC)) {	
 
	// work out long/lat on image
	$pos_x = (int)(($img_x/2) + (($row['long']/180)*($img_x/2)));
	$pos_y = (int)(($img_y/2) - (($row['lat']/90)*($img_y/2)));
 
	//if two positions share the same pixel then combine the result 
	if(!isset($data["{$pos_x}_{$pos_y}"])){
		$data["{$pos_x}_{$pos_y}"] = $row['Rows'];
	}else{
		$data["{$pos_x}_{$pos_y}"] += $row['Rows'];
	}
 
    }
    //free result set 
    $result->close();
 
}
 
// close connection 
$mysqli->close();
 
//Size of data array
$count = count($data);
 
echo "\n"; //debug
 
foreach($data as $key=>$value){
	//Decides for each value
	//	$yellow is the light color
	//	$size is the diameter of the light
	if($value>10000){
		$yellow = imagecolorallocatealpha($im, 0xFF, 0xFF, 0x00,0);
		$size = 15;
	}elseif($value>1000){
		$yellow = imagecolorallocatealpha($im, 0xFF, 0xFF, 0x00,0);
		$size = 10;
	}elseif($value>100){
		$yellow = imagecolorallocatealpha($im, 0xFF, 0xFF, 0x00,0);
		$size = 7;
	}else{
		$yellow = imagecolorallocatealpha($im, 0xFF, 0xFF, 0x00,0);
		$size = 5;
	}
 
	// Draw light
	list($pos_x,$pos_y) = split("_",$key);
	imagefilledellipse($im, $pos_x, $pos_y, $size,$size, $yellow);
 
	$i++; //Debug
	echo "\r$i/$count (".number_format(($i/$count)*100,1)."%)";
}
 
echo "\rSaving Image this could take a bit\n";
//save Image 
imagejpeg($im,$imageout);

So there we go, I welcome any comments.