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<?php |
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/** |
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* Class PolylineSimplifyer |
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* |
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* @link https://github.com/mourner/simplify-js |
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* |
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* @created 04.10.2019 |
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* @author smiley <[email protected]> |
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* @copyright 2019 smiley |
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* @license MIT |
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*/ |
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namespace chillerlan\GeoJSON; |
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use function array_fill, array_keys, array_pop, array_push, array_values, count, is_array; |
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class PolylineSimplifyer{ |
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protected array $coords; |
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/** |
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* PolylineSimplifyer constructor. |
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*/ |
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public function __construct(array $polylineCoords){ |
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$this->coords = $polylineCoords; |
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} |
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/** |
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* @throws \chillerlan\GeoJSON\GeoJSONException |
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*/ |
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public function simplify(float $tolerance = 1, bool $highestQuality = false):array{ |
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$coords = array_values($this->coords ?? []); |
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if(count($coords) < 2){ |
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throw new GeoJSONException('not enough points'); |
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} |
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foreach($this->coords as $coord){ |
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if(!is_array($coord) || count($coord) < 2){ |
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throw new GeoJSONException('invalid coords found'); |
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} |
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} |
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$sqTolerance = $tolerance * $tolerance; |
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$points = $highestQuality ? $coords : $this->simplifyRadialDist($coords, $sqTolerance); |
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return $this->simplifyDouglasPeucker($points, $sqTolerance); |
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} |
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/** |
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* basic distance-based simplification |
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*/ |
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protected function simplifyRadialDist(array $points, float $sqTolerance):array{ |
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$prevPoint = $points[0]; |
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$newPoints = [$prevPoint]; |
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$point = null; |
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$len = count($points); |
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for($i = 1; $i < $len; $i++){ |
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$point = $points[$i]; |
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if($this->getSqDist(array_values($point), array_values($prevPoint)) > $sqTolerance){ |
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$newPoints[] = $point; |
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$prevPoint = $point; |
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} |
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} |
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if($prevPoint !== $point){ |
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$newPoints[] = $point; |
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} |
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return $newPoints; |
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} |
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/** |
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* square distance between 2 points |
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*/ |
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protected function getSqDist(array $p1, array $p2):float{ |
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$dx = $p1[0] - $p2[0]; |
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$dy = $p1[1] - $p2[1]; |
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return $dx * $dx + $dy * $dy; |
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} |
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/** |
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* simplification using optimized Douglas-Peucker algorithm with recursion elimination |
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*/ |
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protected function simplifyDouglasPeucker(array $points, float $sqTolerance):array{ |
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$len = count($points); |
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$markers = array_fill(0, $len - 1, null); |
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$first = 0; |
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$last = $len - 1; |
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$stack = []; |
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$newPoints = []; |
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$index = 0; |
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$markers[$first] = $markers[$last] = 1; |
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while($last){ |
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$maxSqDist = 0; |
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for($i = $first + 1; $i < $last; $i++){ |
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$sqDist = $this->getSqSegDist( |
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array_values($points[$i]), |
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array_values($points[$first]), |
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array_values($points[$last]) |
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); |
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if($sqDist > $maxSqDist){ |
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$index = $i; |
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$maxSqDist = $sqDist; |
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} |
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} |
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if($maxSqDist > $sqTolerance){ |
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$markers[$index] = 1; |
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array_push($stack, $first, $index, $index, $last); |
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} |
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$last = array_pop($stack); |
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$first = array_pop($stack); |
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} |
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foreach($points as $i => $point){ |
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if($markers[$i]){ |
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$newPoints[] = $point; |
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} |
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} |
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return $newPoints; |
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} |
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/** |
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* square distance from a point to a segment |
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*/ |
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protected function getSqSegDist(array $p, array $p1, array $p2):float{ |
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$x = $p1[0]; |
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$y = $p1[1]; |
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$dx = $p2[0] - $x; |
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$dy = $p2[1] - $y; |
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if((int)$dx !== 0 || (int)$dy !== 0){ |
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$t = (($p[0] - $x) * $dx + ($p[1] - $y) * $dy) / ($dx * $dx + $dy * $dy); |
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if($t > 1){ |
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$x = $p2[0]; |
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$y = $p2[1]; |
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} |
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elseif($t > 0){ |
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$x += $dx * $t; |
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$y += $dy * $t; |
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} |
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} |
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$dx = $p[0] - $x; |
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$dy = $p[1] - $y; |
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return $dx * $dx + $dy * $dy; |
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} |
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} |
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chillerlan /
php-geojson-helpers
