spot/inc/converter.php

<?php

/**
 * GPX to GeoJSON Converter
 * 
 * To convert a gpx file:
 * 1. Add file <file_name>.gpx to geo/ folder
 * 2. Assign file to project: UPDATE projects SET geofile = '<file_name>' WHERE id_project = <id_project>;
 * 3. Load any page
 *
 * To force gpx rebuild:
 * ?a=build_geojson&name=<gpx_file_name>
 */
class Converter extends PhpObject {
	
	public function __construct() {
		parent::__construct(__CLASS__, Settings::DEBUG);
	}
	
	public static function convertToGeoJson($sFileName) {
		$sFileName = basename($sFileName, Gpx::EXT);
		
		$oGpx = new Gpx($sFileName);
		$oGeoJson = new GeoJson($sFileName);
		
		$oGeoJson->buildTracks($oGpx->getTracks());
		if($oGeoJson->isSimplicationRequired()) $oGeoJson->buildTracks($oGpx->getTracks(), true);
		$oGeoJson->saveFile();
		
		return $oGpx->getLog().'<br />'.$oGeoJson->getLog();
	}
	
	public static function isGeoJsonValid($sFileName) {
		$bResult = false;
		$sGeoJsonFilePath = Geo::getFilePath($sFileName, GeoJson::EXT);
		if(file_exists($sGeoJsonFilePath) && filemtime($sGeoJsonFilePath) > filemtime(Geo::getFilePath($sFileName, Gpx::EXT))) $bResult = true;
		return $bResult;
	}
}

class Geo extends PhpObject {
	
	const GEO_FOLDER = 'geo/';
	
	protected $asTracks;
	protected $sFilePath;
	
	public function __construct($sFileName) {
		parent::__construct(get_class($this), Settings::DEBUG, PhpObject::MODE_HTML);
		$this->sFilePath = self::getFilePath($sFileName, static::EXT);
		$this->asTracks = array();
	}
	
	public static function getFilePath($sFileName, $sExt) {
		return self::GEO_FOLDER.$sFileName.$sExt;
	}
	
	public function getLog() {
		return $this->getCleanMessageStack(PhpObject::NOTICE_TAB);
	}
}

class Gpx extends Geo {

	const EXT = '.gpx';
	
	public function __construct($sFileName) {
		parent::__construct($sFileName);
		$this->parseFile();
	}
	
	public function getTracks() {
		return $this->asTracks;
	}
	
	private function parseFile() {
		$this->addNotice('Parsing: '.$this->sFilePath);
		$oXml = simplexml_load_file($this->sFilePath);
		
		//Tracks
		$this->addNotice('Converting  '.count($oXml->trk).' tracks');
		foreach($oXml->trk as $aoTrack) {
			$asTrack = array(
				'name'	=> (string) $aoTrack->name,
				'desc'	=> str_replace("\n", '', ToolBox::fixEOL((strip_tags($aoTrack->desc)))),
				'color'	=> (string) $aoTrack->extensions->children('gpxx', true)->TrackExtension->DisplayColor,
				'points'=> array()
			);
			
			foreach($aoTrack->trkseg as $asSegment) {
				foreach($asSegment as $asPoint) {
					$asTrack['points'][] = array(
						'lon' => (float) $asPoint['lon'],
						'lat' => (float) $asPoint['lat'],
						'ele' => (int) $asPoint->ele
					);
				}
			}
			$this->asTracks[] = $asTrack;
		}
		
		//Waypoints
		$this->addNotice('Ignoring '.count($oXml->wpt).' waypoints');
	}
}

class GeoJson extends Geo {
	
	const EXT = '.geojson';
	const MAX_FILESIZE = 2; //MB
	const MAX_DEVIATION = 0.1; //10%
	
	public function __construct($sFileName) {
		parent::__construct($sFileName);
	}
	
	public function saveFile() {
		$this->addNotice('Saving '.$this->sFilePath);
		file_put_contents($this->sFilePath, $this->buildGeoJson());
	}
	
	public function isSimplicationRequired() {
		//Size in bytes
		$iFileSize = strlen($this->buildGeoJson());
		
		//Convert to MB
		$iFileSize = round($iFileSize / pow(1024, 2), 2);
		
		//Compare with max allowed size
		$bFileTooLarge = ($iFileSize > self::MAX_FILESIZE);
		if($bFileTooLarge) $this->addNotice('Output file is too large ('.$iFileSize.'MB > '.self::MAX_FILESIZE.'MB)');
		
		return $bFileTooLarge;
	}
		
	public function buildTracks($asTracks, $bSimplify=false) {
		$this->addNotice('Creating '.($bSimplify?'Simplified ':'').'GeoJson Tracks');
		
		$this->asTracks = array();
		foreach($asTracks as $asTrackProps) {
			
			//Color mapping
			switch($asTrackProps['color']) {
				case 'DarkBlue':
					$sType = 'main';
					break;
				case 'Magenta':
					if($bSimplify) {
						$this->addNotice('Ignoring Track "'.$asTrackProps['name'].' (off-track)');
						continue 2; //discard tracks
					}
					else {
						$sType = 'off-track';
						break;
					}
				case 'Red':
					$sType = 'hitchhiking';
					break;
				default:
					$this->addNotice('Ignoring Track "'.$asTrackProps['name'].' (unknown color "'.$asTrackProps['color'].'")');
					continue 2; //discard tracks
			}
			
			$asTrack = array(
				'type'	=> 'Feature',
				'properties' => array(
					'name'			=> $asTrackProps['name'],
					'type'			=> $sType,
					'description'	=> $asTrackProps['desc']
				),
				'geometry'		=> array(
					'type'			=> 'LineString',
					'coordinates'	=> array()
				)
			);
			
			//Track points
			$asTrackPoints = $asTrackProps['points'];
			$iPointCount = count($asTrackPoints);
			$iInvalidPointCount = 0;
			foreach($asTrackPoints as $iIndex=>$asPoint) {
				if($bSimplify && $iIndex > 0 && $iIndex < ($iPointCount - 1)) {
					if(!$this->isPointValid($asTrackPoints[$iIndex - 1], $asPoint, $asTrackPoints[$iIndex + 1])) {
						$iInvalidPointCount++;
						continue;
					}
				}
				$asTrack['geometry']['coordinates'][] = array_values($asPoint);
			}
			$this->asTracks[] = $asTrack;
			
			if($iInvalidPointCount > 0) $this->addNotice('Removing '.$iInvalidPointCount.'/'.$iPointCount.' points ('.round($iInvalidPointCount / $iPointCount * 100, 1).'%) from '.$asTrackProps['name']);
		}
	}
	
	private function isPointValid($asPointA, $asPointO, $asPointB) {
		/*	A----O	   Calculate angle AO^OB
				  \	   If angle is within [Pi - 10%; Pi + 10%], O can be discarded
				   \   O is valid otherwise
					B
					                   -> ->     ->     ->	
		Law of Cosines: angle = arccos(OA.OB / ||OA||.||OB||)
		*/
		$fVectorOA = array('lon'=>($asPointA['lon'] - $asPointO['lon']), 'lat'=> ($asPointA['lat'] - $asPointO['lat']));
		$fVectorOB = array('lon'=>($asPointB['lon'] - $asPointO['lon']), 'lat'=> ($asPointB['lat'] - $asPointO['lat']));
		
		$fVectorOAxOB = $fVectorOA['lon'] * $fVectorOB['lon'] + $fVectorOA['lat'] * $fVectorOB['lat'];
		
		$fLengthOA = sqrt(pow($asPointA['lon'] - $asPointO['lon'], 2) + pow($asPointA['lat'] - $asPointO['lat'], 2));
		$fLengthOB = sqrt(pow($asPointO['lon'] - $asPointB['lon'], 2) + pow($asPointO['lat'] - $asPointB['lat'], 2));
		
		$fAngleAOB = acos($fVectorOAxOB/($fLengthOA * $fLengthOB));
		
		return ($fAngleAOB <= (1 - self::MAX_DEVIATION) * M_PI || $fAngleAOB >= (1 + self::MAX_DEVIATION) * M_PI);
	}
	
	private function buildGeoJson() {
		return json_encode(array('features'=>$this->asTracks));
	}
}