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<?php |
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declare(strict_types=1); |
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/** |
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* Simplify Polyline with the Douglas-Peucker-Algorithm |
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* |
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* The Algorithm is described here: |
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* http://en.wikipedia.org/wiki/Ramer%E2%80%93Douglas%E2%80%93Peucker_algorithm |
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* |
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* The formula for the Perpendicular Distance is described here: |
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* http://biodiversityinformatics.amnh.org/open_source/pdc/documentation.php |
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* |
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* @author Marcus Jaschen <[email protected]> |
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* @license https://opensource.org/licenses/MIT |
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* @link https://github.com/mjaschen/phpgeo |
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*/ |
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namespace Location\Processor\Polyline; |
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use Location\Line; |
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use Location\Polyline; |
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use Location\Utility\PerpendicularDistance; |
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/** |
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* Simplify Polyline with the Douglas-Peucker-Algorithm |
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* |
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* @author Marcus Jaschen <[email protected]> |
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* @license https://opensource.org/licenses/MIT |
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* @link https://github.com/mjaschen/phpgeo |
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*/ |
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class SimplifyDouglasPeucker implements SimplifyInterface |
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{ |
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/** |
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* @var float |
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*/ |
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private $tolerance; |
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/** |
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* @param float $tolerance the perpendicular distance threshold in meters |
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*/ |
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public function __construct(float $tolerance) |
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{ |
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$this->tolerance = $tolerance; |
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} |
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/** |
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* @param \Location\Polyline $polyline |
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* |
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* @return \Location\Polyline |
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*/ |
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public function simplify(Polyline $polyline): Polyline |
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{ |
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$resultPolyline = new Polyline(); |
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$simplifiedLine = $this->douglasPeucker($polyline->getPoints()); |
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foreach ($simplifiedLine as $point) { |
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$resultPolyline->addPoint($point); |
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} |
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return $resultPolyline; |
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} |
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/** |
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* @param array $line |
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* |
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* @return array |
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*/ |
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protected function douglasPeucker(array $line): array |
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{ |
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$distanceMax = 0; |
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$index = 0; |
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$lineSize = count($line); |
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$pdCalc = new PerpendicularDistance(); |
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for ($i = 1; $i <= ($lineSize - 2); $i++) { |
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$distance = $pdCalc->getPerpendicularDistance($line[$i], new Line($line[0], $line[$lineSize - 1])); |
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if ($distance > $distanceMax) { |
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$index = $i; |
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$distanceMax = $distance; |
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} |
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} |
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if ($distanceMax > $this->tolerance) { |
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$lineSplitFirst = array_slice($line, 0, $index+1); |
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$lineSplitSecond = array_slice($line, $index, $lineSize-$index); |
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if (count($lineSplitFirst) > 2) { |
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$resultsSplit1 = $this->douglasPeucker($lineSplitFirst); |
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} else { |
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$resultsSplit1 = $lineSplitFirst; |
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} |
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if (count($lineSplitSecond) > 2) { |
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$resultsSplit2 = $this->douglasPeucker($lineSplitSecond); |
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} else { |
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$resultsSplit2 = $lineSplitSecond; |
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} |
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array_pop($resultsSplit1); |
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return array_merge($resultsSplit1, $resultsSplit2); |
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} |
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return [$line[0], $line[$lineSize - 1]]; |
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} |
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} |
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mjaschen /
phpgeo
