PHP Extension to handle common geospatial functions. The extension currently has implementations of the Haversine and Vincenty's formulas for calculating distances, an initial bearing calculation function, a Helmert transformation function to transfer between different supported datums, conversions between polar and Cartesian coordinates, conversions between Degree/Minute/Seconds and decimal degrees, a method to simplify linear geometries, as well as a method to calculate intermediate points on a LineString.
git clone [email protected]:php-geospatial/geospatial.git cd geospatial phpize ./configure --enable-geospatial make sudo make install
Then add the extension to an ini file e.g. /etc/php.ini:
extension = geospatial.so
The extension makes use of the GeoJSON standard format for specifying points as co-ordinates. One important thing to note about this format is that points are specified longitude first i.e. longitude, latitude.
e.g.:
$greenwichObservatory = array( 'type' => 'Point', 'coordinates' => array( -0.001483 , 51.477917); );
$from = array( 'type' => 'Point', 'coordinates' => array( -104.88544, 39.06546 ) ); $to = array( 'type' => 'Point', 'coordinates' => array( -104.80, 39.06546 ) ); var_dump(haversine($to, $from));
Vincenty's formula attempts to provide a more accurate distance between two points than the Haversine formula. Whereas the Haversine formula assumes a spherical earth the Vincenty method models the earth as an ellipsoid:
$flinders = array( 'type' => 'Point', 'coordinates' => array(144.42486788889, -37.951033416667 ) ); $buninyong = array( 'type' => 'Point', 'coordinates' => array(143.92649552778, -37.652821138889 ) ); var_dump(vincenty($flinders, $buninyong));
The Helmert transformation allows for the transformation of points between different datums. It can for instance be used to convert between the WGS84 ellipsoid (GEO_WGS84) used by GPS systems and OSGB36 (GEO_AIRY_1830) used by Ordnance Survey in the UK:
$greenwichObservatory = array( 'type' => 'Point', 'coordinates' => array(-0.0014833333333333 , 51.477916666667) ); $greenwichObservatoryWGS84 = transform_datum($greenwichObservatory, GEO_WGS84, GEO_AIRY_1830); var_dump($greenwichObservatoryWGS84);
The initial_bearing
function calculates the initial bearing to go from the
first to the second point, as expressed in a GeoJSON wrapper:
$from = array( 'type' => 'Point', 'coordinates' => array( 2.351, 48.857 ) ); $to = array( 'type' => 'Point', 'coordinates' => array( 0.119, 52.205 ) ); var_dump(initial_bearing($from, $to));
The range of the resulting heading is 0° to +360°.
These two functions calculate between Polar and Cartesian Coordinates, with results depending on which ellipsoid you use.
From Polar to Cartesian:
$lat = 53.38361111111; $long = 1.4669444444; var_dump(polar_to_cartesian($lat, $long, GEO_AIRY_1830));
And back:
$x = 3810891.6734396; $y = 97591.624686311; $z = 5095766.3939034; $polar = cartesian_to_polar($x, $y, $z, GEO_AIRY_1830); echo round($polar['lat'], 6), PHP_EOL; echo round($polar['long'], 6), PHP_EOL; echo round($polar['height'], 3), PHP_EOL;
From decimal to dms. The second argument is either "longitude" or "latitude":
$dms = decimal_to_dms(-1.034291666667, 'longitude'); var_dump($dms);
Which outputs:
array(4) { ["degrees"]=> int(1) ["minutes"]=> int(2) ["seconds"]=> float(3.4500000011994) ["direction"]=> string(1) "W" }
And back from DMS to decimal, where the fourth argument is either "N", "S", "E", or "W":
$decimal = dms_to_decimal(0, 6, 9, 'S');
Which outputs:
float(-0.1025)
The rdp_simplify
method implements RDP to simplify a LineString
according to a certain accuracy (epsilon). As first argument it takes a
GeoJSON LineString (in PHP variable format), and it outputs a similar
structure but then simplified
The fraction_along_gc_line
function can be used to calculate intermediate
points along a Greater Circle Line. For example if you need to draw lines with
more accuracy with for example Leaflet. The function takes the start and end
coordinates (as GeoJson Point), and calculates the intermediate point along
those line. To calculate the point 25% from the start point to the end point,
you would use:
$point1 = [ 'type' => 'Point', 'coordinates' => [ 5, 10 ] ]; $point2 = [ 'type' => 'Point', 'coordinates' => [ 15, 10 ] ]; var_dump(fraction_along_gc_line($point1, $point2, 0.25));
The interpolate_linestring
functions takes a GeoJSONLineString. If the
Pythagorean distance in degrees between two points in the line than the
epsilon
value, it inserts a new point every epsilon / distance
fraction of the Great Circle Line.
Given the Linestring:
$lineString = [ 'type' => 'Linestring', 'coordinates' => [ [ 5, 10 ], [ 15, 10 ], [ 0, -50 ], ] ];
The following will return an array with 26 elements:
var_dump(interpolate_linestring($lineString, 3));
Five for the first pair, at fractions 0.0
, 0.3
, 0.6
, 0.9
and
1.0
, and then two times, each another 0.0485
fraction along the Great
Circle Line for the second pair.
The geohash_encode function can be used to convert GeoJSON Point to a geohash of a specific length (in this case, 12):
$point = [ 'type' => 'Point', 'coordinates' => [ 16.4, 48.2 ] ]; echo geohash_encode( $point, 12 );
Which outputs:
u2edjnw17enr
Similarly, a hashed coordinates pair can be decoded using geohash_decode function:
var_dump(geohash_decode('u2edjnw17enr')); array(2) { ["type"]=> string(5) "Point" ["coordinates"]=> array(2) { [0]=> float(16.40000006184) [1]=> float(48.199999993667) } }