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<?php |
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/** |
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* PHPCoord. |
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* |
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* @author Doug Wright |
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*/ |
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declare(strict_types=1); |
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namespace PHPCoord\CoordinateOperation; |
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use function assert; |
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use function count; |
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use function min; |
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trait BilinearInterpolation |
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{ |
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protected float $startX; |
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protected float $endX; |
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protected float $startY; |
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protected float $endY; |
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protected int $numberOfColumns; |
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protected int $numberOfRows; |
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protected float $columnGridInterval; |
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protected float $rowGridInterval; |
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public function interpolateBilinear( |
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float $x, |
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float $y |
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): array { |
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$corners = $this->getCornersForBilinear($x, $y); |
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$dx = ($x - $corners['lowerLeft']->getX()) / ($corners['lowerRight']->getX() - $corners['lowerLeft']->getX()); |
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$dy = ($y - $corners['lowerLeft']->getY()) / ($corners['upperLeft']->getY() - $corners['lowerLeft']->getY()); |
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$interpolations = []; |
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for ($i = 0, $count = count($corners['lowerLeft']->getValues()); $i < $count; ++$i) { |
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//Interpolate value at lower row |
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$y0 = $this->interpolateLinearUnitSquare($dx, $corners['lowerLeft']->getValues()[$i], $corners['lowerRight']->getValues()[$i]); |
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//Interpolate value at upper row |
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$y1 = $this->interpolateLinearUnitSquare($dx, $corners['upperLeft']->getValues()[$i], $corners['upperRight']->getValues()[$i]); |
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//Interpolate between rows |
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$xy = $this->interpolateLinearUnitSquare($dy, $y0, $y1); |
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$interpolations[] = $xy; |
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} |
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return $interpolations; |
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} |
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/** |
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* Linear interpolation at point p, where p is between 0 and 1. |
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*/ |
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private function interpolateLinearUnitSquare(float $p, float $valueAt0, float $valueAt1): float |
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{ |
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assert($p >= 0 && $p <= 1); |
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return $valueAt0 * (1 - $p) + $valueAt1 * $p; |
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} |
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/** |
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* @return GridValues[] |
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*/ |
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private function getCornersForBilinear(float $x, float $y): array |
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{ |
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$xIndex = (int) (($x - $this->startX) / $this->columnGridInterval); |
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$yIndex = (int) (($y - $this->startY) / $this->rowGridInterval); |
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$xIndexPlus1 = min($xIndex + 1, $this->numberOfColumns); |
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$yIndexPlus1 = min($yIndex + 1, $this->numberOfRows); |
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return [ |
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'lowerLeft' => $this->getRecord($xIndex, $yIndex), |
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'lowerRight' => $this->getRecord($xIndexPlus1, $yIndex), |
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'upperLeft' => $this->getRecord($xIndex, $yIndexPlus1), |
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'upperRight' => $this->getRecord($xIndexPlus1, $yIndexPlus1), |
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]; |
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} |
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} |
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dvdoug /
PHPCoord
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