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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 PHPCoord\GeographicPoint; |
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use PHPCoord\UnitOfMeasure\Length\Metre; |
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use SplFileObject; |
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use function substr; |
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use function unpack; |
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/** |
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* @see https://vdatum.noaa.gov/docs/gtx_info.html for documentation |
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*/ |
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class GTXGrid extends SplFileObject |
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{ |
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private float $startLatitude; |
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private float $startLongitude; |
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private float $latitudeGridInterval; |
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private float $longitudeGridInterval; |
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private int $numberLatitudes; |
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private int $numberLongitudes; |
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private int $headerLength; |
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private string $offsetDataType; |
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public function __construct($filename) |
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{ |
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parent::__construct($filename); |
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$header = $this->getHeader(); |
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$this->startLatitude = $header['xlatsw']; |
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$this->startLongitude = $header['xlonsw']; |
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$this->latitudeGridInterval = $header['dlat']; |
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$this->longitudeGridInterval = $header['dlon']; |
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$this->numberLatitudes = $header['nlat']; |
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$this->numberLongitudes = $header['nlon']; |
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if ($this->startLongitude > 180) { // normalise if necessary |
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$this->startLongitude -= 360; |
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} |
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} |
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/** |
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* Converted from NOAA FORTRAN. |
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*/ |
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public function getAdjustment(GeographicPoint $point): Metre |
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{ |
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$latitude = $point->getLatitude()->getValue(); |
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$longitude = $point->getLongitude()->getValue(); |
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$latitudeIndex = (int) (string) (($latitude - $this->startLatitude) / $this->latitudeGridInterval); |
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$longitudeIndex = (int) (string) (($longitude - $this->startLongitude) / $this->longitudeGridInterval); |
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$corner0 = $this->getRecord($latitudeIndex, $longitudeIndex); |
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$corner1 = $this->getRecord($latitudeIndex + 1, $longitudeIndex); |
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$corner2 = $this->getRecord($latitudeIndex + 1, $longitudeIndex + 1); |
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$corner3 = $this->getRecord($latitudeIndex, $longitudeIndex + 1); |
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$dLatitude = $latitude - ($latitudeIndex * $this->latitudeGridInterval) - $this->startLatitude; |
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$dLongitude = $longitude - ($longitudeIndex * $this->longitudeGridInterval) - $this->startLongitude; |
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$t = $dLatitude / $this->latitudeGridInterval; |
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$u = $dLongitude / $this->longitudeGridInterval; |
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$offset = (1 - $t) * (1 - $u) * $corner0 + ($t) * (1 - $u) * $corner1 + ($t) * ($u) * $corner2 + (1 - $t) * ($u) * $corner3; |
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return new Metre($offset); |
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} |
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public function getRecord(int $latitudeIndex, int $longitudeIndex): float |
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{ |
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$offset = $this->headerLength + ($latitudeIndex * $this->numberLongitudes + $longitudeIndex) * 4; |
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$this->fseek($offset); |
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$rawRow = $this->fread(4); |
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$data = unpack("{$this->offsetDataType}offset", $rawRow); |
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return $data['offset']; |
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} |
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private function getHeader(): array |
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{ |
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$this->fseek(0); |
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$rawHeader = $this->fread(44); |
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$ikind = substr($rawHeader, 40, 4); |
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if (unpack('Nikind', $ikind)['ikind'] === 1) { // big endian |
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$this->headerLength = 44; |
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$this->offsetDataType = 'G'; |
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$data = unpack('Exlatsw/Exlonsw/Edlat/Edlon/Nnlat/Nnlon', $rawHeader); |
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} elseif (unpack('Vikind', $ikind)['ikind'] === 1) { // little endian |
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$this->headerLength = 44; |
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$this->offsetDataType = 'g'; |
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$data = unpack('exlatsw/exlonsw/edlat/edlon/Vnlat/Vnlon', $rawHeader); |
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} else { // not all files (e.g. NZ) have this endian check column, assume big endian |
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$this->headerLength = 40; |
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$this->offsetDataType = 'G'; |
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$data = unpack('Exlatsw/Exlonsw/Edlat/Edlon/Nnlat/Nnlon', $rawHeader); |
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} |
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return $data; |
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} |
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} |
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dvdoug /
PHPCoord
