PHP GeoCalc will calculate the distance in
kilometers and the azimuth between two Latitude/Longitude locations. It
will also calculate kilometers per degrees latitude/longitude and
degrees latitude/longitude per kilometer for a given location.
Geographic Distance and Azimuth Calculations
GeoCalc
is a PHP and (MySQL) API that is useful in performing distance
calculations between two distinct points on the earth's surface. Used
in most GIS (Geographic Information Systems), these are standard
algorithms with various levels of accuracy. Simple example of uses for
this software would be to find the nearest store location to you, or
finding the straight-line distance between two points on a map.
The GeoCalc library is available for download at the bottom of this page.
Methods
The following methods are available in the API. All code samples below are written in PHP.
Basic Methods
| 01 |
// The default constructor |
| 04 |
// Using the Great Circle formula, calculate the distance in |
| 05 |
// kilometers between Latitude/Longitude 1 and Latitude/Longitude 2 |
| 06 |
GCDistance($lat1, $lon1, $lat2, $lon2) |
| 08 |
// Using the Great Circle formula, calculate the azimuth between |
| 09 |
// Latitude/Longitude 1 and Latitude/Longitude 2 |
| 10 |
GCAzimuth($lat1, $lon1, $lat2, $lon2) |
| 12 |
// Using the Ellipsoidal Approximation formula, calculate the distance |
| 13 |
// in kilometers between Latitude/Longitude 1 and Latitude/Longitude 2 |
| 14 |
ApproxDistance($lat1, $lon1, $lat2, $lon2) |
| 16 |
// Using the Ellipsoidal Distance formula, calculate the distance in |
| 17 |
// kilometers between Latitude/Longitude 1 and Latitude/Longitude 2. |
| 18 |
// This formula is the most accurate, as it accounts for the "egg-like" |
| 20 |
EllipsoidDistance($lat1, $lon1, $lat2, $lon2) |
Basic Methods
| 01 |
// Get the number of Kilometers per degree longitude at the given latitude. |
| 02 |
getKmPerLonAtLat($dLatitude) |
| 04 |
// Get the number of degrees longitude per kilometer at the given latitude. |
| 05 |
getLonPerKmAtLat($dLatitude) |
| 07 |
// Get the number of kilometers per degree latitude (average of 111.0 |
| 08 |
// kilometers per degree of latitude) |
| 11 |
// Get the number of degrees latitude per kilometer (average of |
| 12 |
// 1/111 degrees per kilometer) |
Helper Function
| 1 |
ConvKilometersToMiles($dValue) // Convert a distance from kilometers to miles (km / 1.609344 = miles).
|
Examples
Here are some example uses for this class:
| 01 |
include_once("GeoCalc.class.php"); |
| 04 |
// Great Circle Distance |
| 05 |
$dDist = $oGC->GCDistance(38.9333,-94.3253,38.9314,-94.4876); |
| 07 |
// Great Circle Azimuth |
| 08 |
$dDist = $oGC->GCAzimuth(38.9333,-94.3253,38.9314,-94.4876); |
| 10 |
// Approximate Ellipsoid Distance |
| 11 |
$dDist = $oGC->ApproxDistance(38.9333,-94.3253,38.9314,-94.4876); |
| 13 |
// Accurate Ellipsoid Distance |
| 14 |
$dDist = $oGC->EllipsoidDistance(38.9333,-94.3253,38.9314,-94.4876); |
| 16 |
// Convert distance from kilometers to miles |
| 17 |
$dDistMiles = ConvKilometersToMiles($dDist); |
| 19 |
// Advanced Calculation: |
| 20 |
// The following will search for ZIP codes |
| 21 |
// within a radius (roughly calculated) |
| 23 |
// Define the center of the search bounds... |
| 24 |
$dLongitude = -94.44590241; |
| 27 |
// Define the maximum search distance |
| 28 |
$dRadius = 100.00; // in kilometers |
| 30 |
// Calculate the boundary distance in degrees longitude / latitude |
| 31 |
$dAddLat = $oGC->getLatPerKm() * $dRadius; |
| 32 |
$dAddLon = $oGC->getLonPerKmAtLat($dLatitude) * $dRadius; |
| 34 |
// Calculate the boundaries |
| 35 |
$dNorthBounds = $dLatitude + $dAddLat; |
| 36 |
$dSouthBounds = $dLatitude - $dAddLat; |
| 37 |
$dWestBounds = $dLongitude - $dAddLon; |
| 38 |
$dEastBounds = $dLongitude + $dAddLon; |
| 40 |
print "Center Longitude: $dLongitude\n"; |
| 41 |
print "Center Latitude: $dLatitude\n"; |
| 42 |
print "Radius: $dRadius kilometers\n"; |
| 44 |
print "North Bounds: $dNorthBounds\n"; |
| 45 |
print "South Bounds: $dSouthBounds\n"; |
| 46 |
print "East Bounds: $dEastBounds\n"; |
| |
print "West Bounds: $dWestBounds\n";
|
| 49 |
// Sample SQL query statement based on above boundaries: |
| 50 |
$strQuery = "SELECT * FROM PostalCodes " . |
| 51 |
"WHERE Latitude > $dSouthBounds " . |
| 52 |
"AND Latitude < $dNorthBounds " . |
| 53 |
"AND Longitude > $dWestBounds " . |
| 54 |
"AND Longitude < $dEastBounds"; |
For Additional Performance
Using MySQL User Defined Functions (UDF), it is possible to speed up
the execution of your distance calculation queries. The performance
increase is achieved by relying on a pre-compiled, native library being
linked into a running MySQL server.
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