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<?php |
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/* |
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* This file is part of the Runalyze DEM Reader. |
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* |
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* (c) RUNALYZE <[email protected]> |
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* |
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* This source file is subject to the MIT license that is bundled |
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* with this source code in the file LICENSE. |
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*/ |
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namespace Runalyze\DEM\Provider\GeoTIFF; |
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use Runalyze\DEM\Exception\RuntimeException; |
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use Runalyze\DEM\Provider\AbstractResourceReader; |
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class GeoTIFFReader extends AbstractResourceReader |
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{ |
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/** |
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* The number of bytes required to hold a TIFF offset address. |
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* @var int |
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*/ |
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const LEN_OFFSET = 4; |
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/** |
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* The number of bytes containing each item of elevation data |
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* (= BitsPerSample tag value / 8). |
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* @var int |
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*/ |
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const BYTES_PER_SAMPLE = 2; |
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/** |
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* Magic number located at bytes 2-3 which identifies a TIFF file. |
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* @var int |
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*/ |
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const MAGIC_TIFF_ID = 42; |
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/** @var int */ |
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const TIFF_CONST_STRIPOFSETS = 273; |
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/** @var int */ |
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const TIFF_CONST_IMAGE_WIDTH = 256; |
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/** @var int */ |
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const TIFF_CONST_IMAGE_LENGTH = 257; |
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/** @var int */ |
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const TIFF_CONST_STRIPBYTECOUNTS = 279; |
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/** @var int */ |
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const TIFF_CONST_IFD_ENTRY_BYTES = 12; |
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/** @var string */ |
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const BIG_ENDIAN = 'MM'; |
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/** @var string */ |
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const LITTLE_ENDIAN = 'II'; |
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/** @var int */ |
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const UNKNOWN = -32768; |
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/** @var int */ |
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protected $NumDataRows; |
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/** @var int */ |
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protected $NumDataCols; |
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/** @var int */ |
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protected $StripOffsets; |
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/** @var string */ |
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protected $ByteOrder; |
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public function readHeader() |
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{ |
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$this->checkByteOrderAndTiffIdentifier(); |
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$this->goToIFDEntries(); |
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$this->readIFDEntries(); |
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} |
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/** |
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* Go to the file header and work out the byte order (bytes 0-1) and TIFF identifier (bytes 2-3). |
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* @throws RuntimeException |
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*/ |
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protected function checkByteOrderAndTiffIdentifier() |
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{ |
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fseek($this->FileResource, 0); |
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$data = unpack('c2chars/vTIFF_ID', fread($this->FileResource, 4)); |
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if (static::MAGIC_TIFF_ID !== $data['TIFF_ID']) { |
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throw new RuntimeException('Provided GeoTIFF file is not a valid tiff file.'); |
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} |
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$this->ByteOrder = sprintf('%c%c', $data['chars1'], $data['chars2']); |
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if ($this->ByteOrder !== static::LITTLE_ENDIAN && $this->ByteOrder !== static::BIG_ENDIAN) { |
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throw new RuntimeException('Provided GeoTIFF file has an unknown byte order.'); |
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} |
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} |
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/** |
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* The remaining 4 bytes in the header are the offset to the IFD. |
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*/ |
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protected function goToIFDEntries() |
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{ |
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fseek($this->FileResource, 4); |
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$ifdOffsetFormat = $this->isLittleEndian() ? 'VIFDoffset' : 'NIFDoffset'; |
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$data = unpack($ifdOffsetFormat, fread($this->FileResource, 4)); |
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fseek($this->FileResource, $data['IFDoffset']); |
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} |
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/** |
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* Read IFD entries which (the number of entries in each is in the first two bytes). |
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*/ |
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protected function readIFDEntries() |
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{ |
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$countFormat = $this->isLittleEndian() ? 'vcount' : 'ncount'; |
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$countData = unpack($countFormat, fread($this->FileResource, 2)); |
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$ifdFormat = $this->isLittleEndian() ? 'vtag/vtype/Vcount/Voffset' : 'ntag/ntype/Ncount/Noffset'; |
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for ($i = 0; $i < $countData['count']; ++$i) { |
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$constData = unpack($ifdFormat, fread($this->FileResource, static::TIFF_CONST_IFD_ENTRY_BYTES)); |
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switch ($constData['tag']) { |
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case static::TIFF_CONST_IMAGE_WIDTH: |
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$this->NumDataCols = $constData['offset']; |
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break; |
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case static::TIFF_CONST_IMAGE_LENGTH: |
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$this->NumDataRows = $constData['offset']; |
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break; |
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case static::TIFF_CONST_STRIPOFSETS: |
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$this->StripOffsets = $constData['offset']; |
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break; |
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} |
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} |
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} |
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/** |
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* @return bool |
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*/ |
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protected function isLittleEndian() |
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{ |
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return static::LITTLE_ENDIAN === $this->ByteOrder; |
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} |
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/** |
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* @param float $relativeLatitude |
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* @param float $relativeLongitude |
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* @return float[] array(row, col) |
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*/ |
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public function getExactRowAndColFor($relativeLatitude, $relativeLongitude) |
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{ |
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return [ |
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$relativeLatitude * ($this->NumDataRows - 1), |
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$relativeLongitude * ($this->NumDataCols - 1), |
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]; |
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} |
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/** |
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* @param int $row |
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* @param int $col |
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* @return int|bool |
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*/ |
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public function getElevationFor($row, $col) |
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{ |
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fseek($this->FileResource, $this->StripOffsets + ($row * static::LEN_OFFSET)); |
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$firstColumnData = unpack('Voffset', fread($this->FileResource, static::LEN_OFFSET)); |
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fseek($this->FileResource, $firstColumnData['offset'] + $col * static::BYTES_PER_SAMPLE); |
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$elevation = unpack('velevation', fread($this->FileResource, static::BYTES_PER_SAMPLE))['elevation']; |
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return ($elevation <= self::UNKNOWN || $elevation === -self::UNKNOWN) ? false : $elevation; |
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} |
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} |
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Runalyze /
dem-reader
