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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\Point; |
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use DateTimeInterface; |
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use PHPCoord\CoordinateReferenceSystem\Projected; |
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use PHPCoord\Exception\InvalidCoordinateException; |
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use PHPCoord\UnitOfMeasure\Length\Length; |
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use PHPCoord\UnitOfMeasure\Length\Metre; |
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use function floor; |
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use function implode; |
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use function str_pad; |
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use function str_replace; |
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use function strlen; |
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use function strpos; |
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use function substr; |
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use const STR_PAD_LEFT; |
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class BritishNationalGridPoint extends ProjectedPoint |
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{ |
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private const GRID_LETTERS = 'VWXYZQRSTULMNOPFGHJKABCDE'; |
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public function __construct(Length $easting, Length $northing, ?DateTimeInterface $epoch = null) |
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{ |
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parent::__construct(Projected::fromSRID(Projected::EPSG_OSGB36_BRITISH_NATIONAL_GRID), $easting, $northing, null, null, $epoch, null); |
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} |
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/** |
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* @param string $reference OS grid reference (e.g. "TG514131") |
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*/ |
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public static function fromGridReference(string $reference, ?DateTimeInterface $epoch = null): self |
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{ |
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$reference = str_replace(' ', '', $reference); |
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if (strlen($reference) % 2 !== 0) { |
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throw new InvalidCoordinateException('Grid ref must be an even number of characters'); |
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} |
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// first (major) letter is the 500km grid sq, origin at -1000000, -500000 |
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$majorEasting = strpos(self::GRID_LETTERS, $reference[0]) % 5 * 500000 - 1000000; |
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$majorNorthing = floor(strpos(self::GRID_LETTERS, $reference[0]) / 5) * 500000 - 500000; |
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// second (minor) letter is 100km grid sq, origin at 0,0 of this square |
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$minorEasting = strpos(self::GRID_LETTERS, $reference[1]) % 5 * 100000; |
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$minorNorthing = floor(strpos(self::GRID_LETTERS, $reference[1]) / 5) * 100000; |
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// numbers are a division of that square into smaller and smaller pieces |
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$numericPortion = substr($reference, 2); |
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$numericPortionSize = strlen($numericPortion) / 2; |
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$gridSizeInMetres = 1 * (10 ** (5 - $numericPortionSize)); |
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$easting = $majorEasting + $minorEasting + ((int) substr($numericPortion, 0, (int) $numericPortionSize) * $gridSizeInMetres); |
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$northing = $majorNorthing + $minorNorthing + ((int) substr($numericPortion, -(int) $numericPortionSize, (int) $numericPortionSize) * $gridSizeInMetres); |
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return new self(new Metre($easting), new Metre($northing), $epoch); |
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} |
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/** |
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* Grid reference without spaces. e.g. TG514131. |
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*/ |
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public function asGridReference(int $length): string |
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{ |
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return implode('', $this->gridReference($length)); |
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} |
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/** |
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* Grid reference with spaces. e.g. TG 514 131. |
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*/ |
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public function asGridReferenceWithSpaces(int $length): string |
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{ |
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return implode(' ', $this->gridReference($length)); |
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} |
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/** |
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* Convert this grid reference into a grid reference string of a |
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* given length (2, 4, 6, 8 or 10) including the two-character |
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* designation for the 100km square. e.g. TG514131. |
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* |
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* @return array{0: string, 1: string, 2: string} |
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*/ |
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protected function gridReference(int $length): array |
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{ |
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if ($length % 2 !== 0) { |
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throw new InvalidCoordinateException('Chosen length must be an even number'); |
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} |
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if ($length > 10) { |
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throw new InvalidCoordinateException('Grid squares are 100,000m wide, max precision is 10'); |
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} |
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$halfLength = $length / 2; |
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$x = $this->easting->asMetres()->getValue(); |
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$y = $this->northing->asMetres()->getValue(); |
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$easting = str_pad((string) (int) $x, $halfLength + 1, '0', STR_PAD_LEFT); |
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$northing = str_pad((string) (int) $y, $halfLength + 1, '0', STR_PAD_LEFT); |
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$adjustedX = $x + 1000000; |
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$adjustedY = $y + 500000; |
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$majorSquaresEast = floor($adjustedX / 500000); |
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$majorSquaresNorth = floor($adjustedY / 500000); |
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$majorLetterIndex = (int) (5 * $majorSquaresNorth + $majorSquaresEast); |
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$majorLetter = substr(self::GRID_LETTERS, $majorLetterIndex, 1); |
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// second (minor) letter is 100km grid sq, origin at 0,0 of this square |
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$minorSquaresEast = (int) $easting[0] % 5; |
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$minorSquaresNorth = (int) $northing[0] % 5; |
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$minorLetterIndex = (5 * $minorSquaresNorth + $minorSquaresEast); |
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$minorLetter = substr(self::GRID_LETTERS, $minorLetterIndex, 1); |
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return [ |
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$majorLetter . $minorLetter, |
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substr($easting, 1, $halfLength), |
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substr($northing, 1, $halfLength), |
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]; |
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} |
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} |
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dvdoug /
PHPCoord
