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93 lines
3.6 KiB
93 lines
3.6 KiB
<?php
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namespace p3k\geo;
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//RamerDouglasPeucker
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//Reduces the number of points on a polyline by removing those that are closer to the line
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//than the distance $epsilon.
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//The polyline is provided as an array of arrays, where each internal array is one point on the polyline,
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//specified by easting (x-coordinate) with key "0" and northing (y-coordinate) with key "1".
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//It is assumed that the coordinates and distance $epsilon are given in the same units.
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//The result is returned as an array in a similar format.
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//Each point returned in the result array will retain all its original data, including its E and N
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//values along with any others.
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function ramerDouglasPeucker($pointList, $epsilon)
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{
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if(count($pointList) == 0)
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return array();
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// Find the point with the maximum distance
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$dmax = 0;
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$index = 0;
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$totalPoints = count($pointList);
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for ($i = 1; $i < ($totalPoints - 1); $i++)
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{
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$d = perpendicularDistance($pointList[$i][0], $pointList[$i][1],
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$pointList[0][0], $pointList[0][1],
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$pointList[$totalPoints-1][0], $pointList[$totalPoints-1][1]);
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if ($d > $dmax)
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{
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$index = $i;
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$dmax = $d;
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}
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}
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$resultList = array();
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// If max distance is greater than epsilon, recursively simplify
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if ($dmax >= $epsilon)
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{
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// Recursive call
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$recResults1 = ramerDouglasPeucker(array_slice($pointList, 0, $index + 1), $epsilon);
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$recResults2 = ramerDouglasPeucker(array_slice($pointList, $index, $totalPoints - $index), $epsilon);
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// Build the result list
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$resultList = array_merge(array_slice($recResults1, 0, count($recResults1) - 1),
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array_slice($recResults2, 0, count($recResults2)));
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}
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else
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{
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$resultList = array($pointList[0], $pointList[$totalPoints-1]);
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}
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// Return the result
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return $resultList;
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}
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// http://www.loughrigg.org/rdp/
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//The author has placed this work in the Public Domain, thereby relinquishing all copyrights.
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//You may use, modify, republish, sell or give away this work without prior consent.
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//This implementation comes with no warranty or guarantee of fitness for any purpose.
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//=========================================================================
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//An implementation of the Ramer-Douglas-Peucker algorithm for reducing
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//the number of points on a polyline
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//see http://en.wikipedia.org/wiki/Ramer%E2%80%93Douglas%E2%80%93Peucker_algorithm
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//=========================================================================
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//Finds the perpendicular distance from a point to a straight line.
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//The coordinates of the point are specified as $ptX and $ptY.
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//The line passes through points l1 and l2, specified respectively with their
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//coordinates $l1x and $l1y, and $l2x and $l2y
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function perpendicularDistance($ptX, $ptY, $l1x, $l1y, $l2x, $l2y)
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{
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$result = 0;
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if ($l2x == $l1x)
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{
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//vertical lines - treat this case specially to avoid divide by zero
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$result = abs($ptX - $l2x);
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}
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else
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{
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$slope = (($l2y-$l1y) / ($l2x-$l1x));
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$passThroughY = (0-$l1x)*$slope + $l1y;
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$result = (abs(($slope * $ptX) - $ptY + $passThroughY)) / (sqrt($slope*$slope + 1));
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}
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return $result;
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}
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// Calculate the Great Circle distance between two points, in meters
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function gc_distance($lat1, $lng1, $lat2, $lng2) {
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return ( 6378100 * acos( cos( deg2rad($lat1) ) * cos( deg2rad($lat2) ) * cos( deg2rad($lng2) - deg2rad($lng1) ) + sin( deg2rad($lat1) ) * sin( deg2rad($lat2) ) ) );
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}
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