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<?php
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// $Id: geonames_cck_earth.inc,v 1.2 2008/08/04 16:34:26 thegreenman Exp $
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// Trigonometry for calculating geographical distances.
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// All function arguments and return values measure distances in metres
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// and angles in degrees. The ellipsoid model is from the WGS-84 datum.
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// Ka-Ping Yee, 2003-08-11
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//$earth_radius_semimajor = 6378137.0;
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//$earth_flattening = 1/298.257223563;
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//$earth_radius_semiminor = $earth_radius_semimajor * (1 - $earth_flattening);
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//$earth_eccentricity_sq = 2*$earth_flattening - pow($earth_flattening, 2);
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// I don't know what's up: PHP is hating on my global variables (commented out above),
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// so I have to write functions that return them! (-Ankur)
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// Commenting out the global variables above and replacing them with functions that
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// return the same values is the only thing I changed since, for some reason, my
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// PHP wasn't acknowledging these global variables.
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// This library is an original implementation of UCB CS graduate student, Ka-Ping Yee (http://www.zesty.ca).
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function earth_radius_semimajor() {
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return 6378137.0;
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}
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function earth_flattening() {
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return (1/298.257223563);
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}
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function earth_radius_semiminor() {
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return (earth_radius_semimajor() * (1 - earth_flattening()));
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}
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function earth_eccentricity_sq() {
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return (2*earth_flattening() - pow(earth_flattening(), 2));
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}
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// Latitudes in all of U. S.: from -7.2 (American Samoa) to 70.5 (Alaska).
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// Latitudes in continental U. S.: from 24.6 (Florida) to 49.0 (Washington).
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// Average latitude of all U. S. zipcodes: 37.9.
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function earth_radius($latitude=37.9) {
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//global $earth_radius_semimajor, $earth_radius_semiminor;
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// Estimate the Earth's radius at a given latitude.
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// Default to an approximate average radius for the United States.
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$lat = deg2rad($latitude);
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$x = cos($lat)/earth_radius_semimajor();
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$y = sin($lat)/earth_radius_semiminor();
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return 1 / (sqrt($x*$x + $y*$y));
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}
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function earth_xyz($longitude, $latitude, $height = 0) {
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// Convert longitude and latitude to earth-centered earth-fixed coordinates.
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// X axis is 0 long, 0 lat; Y axis is 90 deg E; Z axis is north pole.
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//global $earth_radius_semimajor, $earth_eccentricity_sq;
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$long = deg2rad($longitude);
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$lat = deg2rad($latitude);
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$coslong = cos($long);
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$coslat = cos($lat);
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$sinlong = sin($long);
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$sinlat = sin($lat);
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$radius = earth_radius_semimajor() /
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sqrt(1 - earth_eccentricity_sq() * $sinlat * $sinlat);
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$x = ($radius + $height) * $coslat * $coslong;
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$y = ($radius + $height) * $coslat * $sinlong;
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$z = ($radius * (1 - earth_eccentricity_sq()) + $height) * $sinlat;
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return array($x, $y, $z);
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}
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function earth_arclength($angle, $latitude=37.9) {
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// Convert a given angle to earth-surface distance.
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return deg2rad($angle) * earth_radius($latitude);
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}
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function earth_distance($longitude1, $latitude1, $longitude2, $latitude2) {
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// Estimate the earth-surface distance between two locations.
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$long1 = deg2rad($longitude1);
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$lat1 = deg2rad($latitude1);
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$long2 = deg2rad($longitude2);
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$lat2 = deg2rad($latitude2);
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$radius = earth_radius(($latitude1 + $latitude2) / 2);
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$cosangle = cos($lat1)*cos($lat2) *
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(cos($long1)*cos($long2) + sin($long1)*sin($long2)) +
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sin($lat1)*sin($lat2);
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return acos($cosangle) * $radius;
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}
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/*
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* Returns the SQL fragment needed to add a column called 'distance'
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* to a query that includes the location table
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*
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* @param $longitude The measurement point
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* @param $latibude The measurement point
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* @param $tbl_alias If necessary, the alias name of the location table to work from. Only required when working with named {location} tables
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*/
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function earth_distance_sql($longitude, $latitude, $tbl_alias, $latcol, $lngcol) {
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// Make a SQL expression that estimates the distance to the given location.
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$long = deg2rad($longitude);
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$lat = deg2rad($latitude);
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$radius = earth_radius($latitude);
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// If the table alias is specified, add on the separator.
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$tbl_alias = empty($tbl_alias) ? $tbl_alias : ($tbl_alias .'.');
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$coslong = cos($long);
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$coslat = cos($lat);
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$sinlong = sin($long);
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$sinlat = sin($lat);
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return "(IFNULL(ACOS($coslat*COS(RADIANS({$tbl_alias}$latcol))*($coslong*COS(RADIANS({$tbl_alias}$lngcol)) + $sinlong*SIN(RADIANS({$tbl_alias}$lngcol))) + $sinlat*SIN(RADIANS({$tbl_alias}$latcol))), 0.00000)*$radius)";
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}
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/*
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* Returns the SQL fragment needed to add a column called 'distanceSquared'
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* to a query that includes the location table
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*
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* @param $longitude The measurement point
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* @param $latibude The measurement point
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* @param $tbl_alias If necessary, the alias name of the location table to work from. Only required when working with named {location} tables
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*/
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function earth_distancesqlared_sql($longitude, $latitude, $tbl_alias, $latcol, $lngcol) {
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// Make a SQL expression that estimates the distance to the given location.
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$long = deg2rad($longitude);
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$lat = deg2rad($latitude);
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// If the table alias is specified, add on the separator.
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$tbl_alias = empty($tbl_alias) ? $tbl_alias : ($tbl_alias .'.');
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return "(POW($lat - RADIANS({$tbl_alias}$latcol), 2) + POW($long - RADIANS({$tbl_alias}$lngcol), 2))";
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}
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function earth_longitude_range($longitude, $latitude, $distance) {
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// Estimate the min and max longitudes within $distance of a given location.
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$long = deg2rad($longitude);
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$lat = deg2rad($latitude);
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$radius = earth_radius($latitude);
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$angle = $distance / $radius;
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$diff = asin(sin($angle)/cos($lat));
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$minlong = $long - $diff;
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$maxlong = $long + $diff;
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if ($minlong < -pi()) { $minlong = $minlong + pi()*2; }
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if ($maxlong > pi()) { $maxlong = $maxlong - pi()*2; }
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return array(rad2deg($minlong), rad2deg($maxlong));
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}
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function earth_latitude_range($longitude, $latitude, $distance) {
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// Estimate the min and max latitudes within $distance of a given location.
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$long = deg2rad($longitude);
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$lat = deg2rad($latitude);
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$radius = earth_radius($latitude);
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$angle = $distance / $radius;
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$minlat = $lat - $angle;
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$maxlat = $lat + $angle;
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$rightangle = pi()/2;
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if ($minlat < -$rightangle) { // wrapped around the south pole
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$overshoot = -$minlat - $rightangle;
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$minlat = -$rightangle + $overshoot;
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if ($minlat > $maxlat) { $maxlat = $minlat; }
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$minlat = -$rightangle;
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}
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if ($maxlat > $rightangle) { // wrapped around the north pole
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$overshoot = $maxlat - $rightangle;
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$maxlat = $rightangle - $overshoot;
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if ($maxlat < $minlat) { $minlat = $maxlat; }
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$maxlat = $rightangle;
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}
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return array(rad2deg($minlat), rad2deg($maxlat));
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}
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