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https://github.com/php-geospatial/geospatial

PHP Extension to handle common geospatial functions.
https://github.com/php-geospatial/geospatial

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PHP Extension to handle common geospatial functions.

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README 

        
=====================================

geospatial - PHP Geospatial Extension

=====================================

.. image:: https://travis-ci.org/php-geospatial/geospatial.svg?branch=master

    :target: https://travis-ci.org/php-geospatial/geospatial

.. image:: https://codecov.io/gh/php-geospatial/geospatial/branch/master/graphs/badge.svg?branch=master

    :target: https://codecov.io/github/php-geospatial/geospatial?branch=master



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.



Instalation

===========



::



    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



Usage

=====



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);

    );



Haversine

---------



::



    $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

------------------



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));



Helmert Transformation

----------------------



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);



Calculating Initial Bearing

---------------------------



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°.



Converting between polar and Cartesian Coordinates

--------------------------------------------------



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;



Converting between Degree/Min/Sec and Decimal coordinates

---------------------------------------------------------



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)



Simplifying LineStrings

-----------------------



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



.. _RDP: https://en.wikipedia.org/wiki/Ramer%E2%80%93Douglas%E2%80%93Peucker_algorithm



Interpolation along a Greater Circle Line

-----------------------------------------



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));



Interpolating a GeoJSONLineString

---------------------------------



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.



Geohashing

----------



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)

	  }

	}