Encoding Polylines for Google Maps

PolylineEncoder.php

<?php

// http://facstaff.unca.edu/mcmcclur/GoogleMaps/EncodePolyline/

$numLevels = 18;
$zoomFactor = 2;
$verySmall = 0.00001;
$forceEndpoints = true;

for($i = 0; $i < $numLevels; $i++) 
{
	$zoomLevelBreaks[$i] = $verySmall*pow($zoomFactor, $numLevels-$i-1);
}

function computeLevel($dd)
{
    global $verySmall, $zoomLevelBreaks;

    if($dd > $verySmall)
    {
        $lev = 0;
        while($dd < $zoomLevelBreaks[$lev])
	{
	    $lev++;
	}
    }
    return $lev;
}
function dpEncode($points) 
{
    global $verySmall;

    if(count($points) > 2) 
    {
	$stack[] = array(0, count($points)-1);
	while(count($stack) > 0) 
	{
	    $current = array_pop($stack);
	    $maxDist = 0;
	    for($i = $current[0]+1; $i < $current[1]; $i++)
	    {
	    	$temp = distance($points[$i], $points[$current[0]], $points[$current[1]]);
		if($temp > $maxDist)
		{
		    $maxDist = $temp;
		    $maxLoc = $i;
		    if($maxDist > $absMaxDist) 
		    {
		        $absMaxDist = $maxDist;
		    }
		}
	    }
	    if($maxDist > $verySmall)
	    {
	    	$dists[$maxLoc] = $maxDist;
		array_push($stack, array($current[0], $maxLoc));
		array_push($stack, array($maxLoc, $current[1]));
	    }
	}
    }

    $encodedPoints = createEncodings($points, $dists);
    $encodedLevels = encodeLevels($points, $dists, $absMaxDist);
    $encodedPointsLiteral = str_replace('\\',"\\\\",$encodedPoints);

    return array($encodedPoints, $encodedLevels, $encodedPointsLiteral);
}

function distance($p0, $p1, $p2)
{
    if($p1[0] == $p2[0] && $p1[1] == $p2[1])
    {
        $out = sqrt(pow($p2[0]-$p0[0],2) + pow($p2[1]-$p0[1],2));
    }
    else
    {
        $u = (($p0[0]-$p1[0])*($p2[0]-$p1[0]) + ($p0[1]-$p1[1]) * ($p2[1]-$p1[1])) / (pow($p2[0]-$p1[0],2) + pow($p2[1]-$p1[1],2));
        if($u <= 0)
        {
            $out = sqrt(pow($p0[0] - $p1[0],2) + pow($p0[1] - $p1[1],2));
        }
        if($u >= 1) 
	{
            $out = sqrt(pow($p0[0] - $p2[0],2) + pow($p0[1] - $p2[1],2));
        }
        if(0 < $u && $u < 1) 
	{
            $out = sqrt(pow($p0[0]-$p1[0]-$u*($p2[0]-$p1[0]),2) + pow($p0[1]-$p1[1]-$u*($p2[1]-$p1[1]),2));
        }
    }
    return $out;
}

function encodeSignedNumber($num)
{
   $sgn_num = $num << 1;
   if ($num < 0) 
   {
       $sgn_num = ~($sgn_num);
   }
   return encodeNumber($sgn_num);
}

function createEncodings($points, $dists)
{
    for($i=0; $i<count($points); $i++)
    {
        if(isset($dists[$i]) || $i == 0 || $i == count($points)-1) 
	{
	    $point = $points[$i];
	    $lat = $point[0];
	    $lng = $point[1];
	    $late5 = floor($lat * 1e5);
	    $lnge5 = floor($lng * 1e5);
	    $dlat = $late5 - $plat;
	    $dlng = $lnge5 - $plng;
	    $plat = $late5;
	    $plng = $lnge5;
	    $encoded_points .= encodeSignedNumber($dlat) . encodeSignedNumber($dlng);
	}
    }
    return $encoded_points;
}

function encodeLevels($points, $dists, $absMaxDist) 
{
    global $numLevels, $forceEndpoints;

    if($forceEndpoints)
    {
        $encoded_levels .= encodeNumber($numLevels-1);
    }
    else
    {
        $encoded_levels .= encodeNumber($numLevels-computeLevel($absMaxDist)-1);    
    }
    for($i=1; $i<count($points)-1; $i++)
    {
        if(isset($dists[$i]))
	{
	    $encoded_levels .= encodeNumber($numLevels-computeLevel($dists[$i])-1);
	}
    }
    if($forceEndpoints)
    {
        $encoded_levels .= encodeNumber($numLevels -1);
    }
    else
    {
        $encoded_levels .= encodeNumber($numLevels-computeLevel($absMaxDist)-1);
    }
    return $encoded_levels;
}

function encodeNumber($num)
{
    while($num >= 0x20) 
    {
        $nextValue = (0x20 | ($num & 0x1f)) + 63;
        $encodeString .= chr($nextValue);
	$num >>= 5;
    }
    $finalValue = $num + 63;
    $encodeString .= chr($finalValue);
    return $encodeString;
}

?>