I have been working for about a year on a website designed to deliver GPS data about hiking trails to end users. I usually shy away from posting code; however, this is mostly not my code and the theory behind it comes from an article on DevGuru speaking directly to this. I was also able to locate a PHP port of this, to which I in term made some minor modifications (I like to think they are improvements!). The major shortcoming that I see with using PHP to perform any form of GIS calculations is limitations of PHP when it comes to calculating large numbers. There are some “big number” libraries available, however, I didn’t care to take the time to convert the code to use these, AND the question is ultimately raised, do you really want a web server having to use precious processing cycles on calculations best performed within a GIS. (The correct tool for the correct situation.) PHP’s float serves the accuracy needs of my purposes, and I use the library to produce an xml, gpx, and kml file for end user consumption. This minimizes the usage of a potentially processor intensive library, while providing me the conveniences of a web based management console. My primary modification was to eliminate an object constant used as a multiplier to convert the latitude and longitude values to radians (required for PHP’s trigonometry functions), and use PHP’s deg2rad function. I also upgraded the library to use PHP5’s OO functionality, and then added a function that is useful for calculating short distances. It takes elevation difference into account, but uses a Pythagorean approach to solving the distance question, failing to account for the curvature of the surface of the earth. (VERY useful for dealing with GPS tracks.)
<?php if (!defined('BASEPATH')) exit('No direct script access allowed');
/**
* Code Igniter
*
* An open source application development framework for PHP 4.3.2 or newer
*
* @package CodeIgniter
* @author Dariusz Debowczyk
* @copyright Copyright (c) 2006, D.Debowczyk
* @license http://www.codeignitor.com/user_guide/license.html
* @link http://www.codeigniter.com
* @since Version 1.0
* @filesource
*/
// ------------------------------------------------------------------------
/**
* GeoCalc - Geographic Calculator
*
* This code was converted to PHP from Visual C++
* by Steven Brendtro on behalf of imaginerc.com
* and updated to a PHP5 library for use with Code
* Igniter by Paul Edwin Mastin, adding a short distance
* calculator with height calculations
*
* The original code and an article can be found
* on CodeGuru at:
* http://www.codeguru.com/Cpp/Cpp/algorithms/print.php/c5115/
*
* @package CodeIgniter
* @subpackage Libraries
* @category GeoCalc - Geographic Calculator
* @author Steven Brendtro, Paul Edwin Mastin
* @link http://www.bunkertrails.org/wiki
*/
class GeoCalc {
const PI = 3.14159265359;
const TWOPI = 6.28318530718;
const DE2RA = 0.01745329252;
const RA2DE = 57.2957795129;
const ERAD = 6378.135;
const ERADM = 6378135.0;
const AVG_ERAD = 6371.0;
const EPS = 0.000000000005;
const KM2MI = 0.621371;
public $FLATTENING = 0;
public function __construct() {
$this->FLATTENING = 1.0/298.26; // Earth flattening
// (WGS 1972)
return;
}
function GCDistance($lat1, $lon1, $lat2, $lon2) {
$lat1 = deg2rad($lat1);
$lon1 = deg2rad($lon1);
$lat2 = deg2rad($lat2);
$lon2 = deg2rad($lon2);
$d = sin($lat1)*sin($lat2) + cos($lat1)*cos($lat2)*cos($lon1 - $lon2);
return (self::AVG_ERAD * acos($d));
}
function GCAzimuth($lat1, $lon1, $lat2, $lon2) {
$result = 0.0;
$ilat1 = intval(0.50 + $lat1 * 360000.0);
$ilat2 = intval(0.50 + $lat2 * 360000.0);
$ilon1 = intval(0.50 + $lon1 * 360000.0);
$ilon2 = intval(0.50 + $lon2 * 360000.0);
$lat1 = deg2rad($lat1);
$lon1 = deg2rad($lon1);
$lat2 = deg2rad($lat2);
$lon2 = deg2rad($lon2);
if (($ilat1 == $ilat2) && ($ilon1 == $ilon2)) {
return result;
}
else if ($ilat1 == $ilat2) {
if ($ilon1 > $ilon2) $result = 90.0;
else $result = 270.0;
}
else if ($ilon1 == $ilon2) {
if ($ilat1 > $ilat2) $result = 180.0;
}
else {
$c = acos(sin($lat2)*sin($lat1) + cos($lat2)*cos($lat1)*cos(($lon2-$lon1)));
$A = asin(cos($lat2)*sin(($lon2-$lon1))/sin($c));
$result = deg2rad($A);
if (($ilat2 > $ilat1) && ($ilon2 > $ilon1)) $result = $result;
else if (($ilat2 < $ilat1) && ($ilon2 < $ilon1)) $result = 180.0 - $result;
else if (($ilat2 < $ilat1) && ($ilon2 > $ilon1)) $result = 180.0 - $result;
else if (($ilat2 > $ilat1) && ($ilon2 < $ilon1)) $result += 360.0;
}
return $result;
}
function ApproxDistance($lat1, $lon1, $lat2, $lon2) {
$lat1 = deg2rad($lat1);
$lon1 = -deg2rad($lon1);
$lat2 = deg2rad($lat2);
$lon2 = -deg2rad($lon2);
$F = ($lat1 + $lat2) / 2.0;
$G = ($lat1 - $lat2) / 2.0;
$L = ($lon1 - $lon2) / 2.0;
$sing = sin($G);
$cosl = cos($L);
$cosf = cos($F);
$sinl = sin($L);
$sinf = sin($F);
$cosg = cos($G);
$S = $sing*$sing*$cosl*$cosl + $cosf*$cosf*$sinl*$sinl;
$C = $cosg*$cosg*$cosl*$cosl + $sinf*$sinf*$sinl*$sinl;
$W = atan2(sqrt($S),sqrt($C));
$R = sqrt(($S*$C))/$W;
$H1 = (3 * $R - 1.0) / (2.0 * $C);
$H2 = (3 * $R + 1.0) / (2.0 * $S);
$D = 2 * $W * self::ERAD;
$return = ($D * (1 + $this->FLATTENING * $H1 * $sinf*$sinf*$cosg*$cosg - $this->FLATTENING*$H2*$cosf*$cosf*$sing*$sing));
return $return;
}
function EllipsoidDistance($lat1, $lon1, $lat2, $lon2) {
$distance = 0.0;
$faz = 0.0;
$baz = 0.0;
$r = 1.0 - $this->FLATTENING;
$tu1 = 0.0;
$tu2 = 0.0;
$cu1 = 0.0;
$su1 = 0.0;
$cu2 = 0.0;
$x = 0.0;
$sx = 0.0;
$cx = 0.0;
$sy = 0.0;
$cy = 0.0;
$y = 0.0;
$sa = 0.0;
$c2a = 0.0;
$cz = 0.0;
$e = 0.0;
$c = 0.0;
$d = 0.0;
$cosy1 = 0.0;
$cosy2 = 0.0;
if(($lon1 == $lon2) && ($lat1 == $lat2)) return $distance;
$lat1 = deg2rad($lat1);
$lon1 = deg2rad($lon1);
$lat2 = deg2rad($lat2);
$lon2 = deg2rad($lon2);
$cosy1 = cos($lat1);
$cosy2 = cos($lat2);
if($cosy1 == 0.0) $cosy1 = 0.0000000001;
if($cosy2 == 0.0) $cosy2 = 0.0000000001;
$tu1 = $r * sin($lat1) / $cosy1;
$tu2 = $r * sin($lat2) / $cosy2;
$cu1 = 1.0 / sqrt($tu1 * $tu1 + 1.0);
$su1 = $cu1 * $tu1;
$cu2 = 1.0 / sqrt($tu2 * $tu2 + 1.0);
$x = $lon2 - $lon1;
$distance = $cu1 * $cu2;
$baz = $distance * $tu2;
$faz = $baz * $tu1;
while(abs($d - $x) > self::EPS) {
$sx = sin($x);
$cx = cos($x);
$tu1 = $cu2 * $sx;
$tu2 = $baz - $su1 * $cu2 * $cx;
$sy = sqrt($tu1 * $tu1 + $tu2 * $tu2);
$cy = $distance * $cx + $faz;
$y = atan2($sy, $cy);
$sa = $distance * $sx / $sy;
$c2a = - $sa * $sa + 1.0;
$cz = $faz + $faz;
if($c2a > 0.0) $cz = - $cz / $c2a + $cy;
$e = $cz * $cz * 2.0 - 1.0;
$c = ((-3.0 * $c2a + 4.0) * $this->FLATTENING + 4.0) * $c2a * $this->FLATTENING / 16.0;
$d = $x;
$x = (($e * $cy * $c + $cz) * $sy * $c + $y) * $sa;
$x = (1.0 - $c) * $x * $this->FLATTENING + $lon2 - $lon1;
}
$x = sqrt((1.0 / $r / $r - 1.0) * $c2a + 1.0) + 1.0;
$x = ($x - 2.0) / $x;
$c = 1.0 - $x;
$c = ($x * $x / 4.0 + 1.0) / $c;
$d = (0.375 * $x * $x - 1.0) * $x;
$x = $e * $cy;
$distance = 1.0 - $e - $e;
$distance = (((($sy * $sy * 4.0 - 3.0) * $distance * $cz * $d / 6.0 - $x) * $d / 4.0 + $cz) * $sy * $d + $y) * $c * self::ERAD * $r;
return $distance;
}
//Short Distance (For distances less than ~10 miles)
function sDistance($input_lat1, $input_lon1, $height1, $input_lat2, $input_lon2, $height2) {
$lat1 = deg2rad($input_lat1);
$lon1 = deg2rad($input_lon1);
$lat2 = deg2rad($input_lat2);
$lon2 = deg2rad($input_lon2);
$height1 = $height1;
$height2 = $height2;
$x1 = (self::ERADM + $height1) * ( cos($lat1) * cos($lon1) );
$y1 = (self::ERADM + $height1) * ( sin($lat1) );
$z1 = (self::ERADM + $height1) * ( cos($lat1) * sin($lon1) );
$x2 = (self::ERADM + $height2) * ( cos($lat2) * cos($lon2) );
$y2 = (self::ERADM + $height2) * ( sin($lat2) );
$z2 = (self::ERADM + $height2) * ( cos($lat2) * sin($lon2) );
$dx = ( $x2 - $x1 );
$dy = ( $y2 - $y1 );
$dz = ( $z2 - $z1 );
return sqrt( ( $dx * $dx ) + ( $dy * $dy ) + ( $dz * $dz ) );
}
function getKmPerLonAtLat($dLatitude) {
// Thanks to Eric Iverson for this correction! Must convert degrees to radians...
$dLatitude = deg2rad($dLatitude);
return 111.321 * cos($dLatitude);
}
function getLonPerKmAtLat($dLatitude) {
return 1 / $this->getKmPerLonAtLat($dLatitude);
}
function getKmPerLat() {
return 111.000;
}
function getLatPerKm() {
return 1 / $this->getKmPerLat();
}
}