geohash.php

<?php

class GeoHash {
  
  private $hash;
  
  private $latitude;
  private $longitude;
  private $precision;
  
  /**
   * Returns the hash
   * @return string
   */
  public function getHash() {
    if(!$this->hash) {
      if(empty($this->latitude)) throw new Exception("Latitude is required");
      if(empty($this->longitude)) throw new Exception("Longitude is required");
      $this->hash = $this->createHash();
    }
    return $this->hash;
  }
  
  /**
   * Set a hash, this will clear any latitude/longitude or precision set
   * @return GeoHash
   */
  public function setHash($hash) {
    $this->hash = $hash;
    $this->parseHash();
    return $this;
  }
  
  /**
   * Get the latitude
   * @return float
   */
  public function getLatitude() {
    return $this->latitude;
  }
  
  /**
   * Set a latitude, this will clear any hash
   * @return GeoHash
   */
  public function setLatitude($latitude) {
    $this->hash = null;
    $this->latitude = $latitude;
    return $this;
  }
  
  /**
   * Get the longitude
   * @return float
   */
  public function getLongitude() {
    return $this->longitude;
  }
  
  /**
   * Set a latitude, this will clear any hash
   * @return GeoHash
   */
  public function setLongitude($longitude) {
    $this->hash = null;
    $this->longitude = $longitude;
    return $this;
  }
  
  /**
   * Gets the precision
   * @return float
   */
  public function getPrecision() {
    return $this->precision;
  }
  
  /**
   * Set a precision, clears any hash
   * @return GeoHash
   */
  public function setPrecision($precision) {
    $this->hash = null;
    $this->precision = $precision;
    return $this;
  }
  
  /**
   * Return the hash, obviously, to print out
   * @return string
   */
  public function __toString() {
    return $this->getHash();
  }
  
  private function clearCoords() {
    $this->latitude  = null;
    $this->longitude = null;
    $this->precision = null;
  }
  
  private function createHash() {
    $table = "0123456789bcdefghjkmnpqrstuvwxyz";
    $lng = $this->longitude;
    $lat = $this->latitude;
    if(isset($this->precision)) {
      $p = $this->precision;
    } else {
      $lap = strlen($lat)-strpos($lat,".");
      $lop = strlen($lng)-strpos($lng,".");
      $p = $this->precision = pow(10,-max($lap-1,$lop-1,0))/2;
    }
    $minlat =  -90;
    $maxlat =   90;
    $minlng = -180;
    $maxlng =  180;
    $latE   =   90;
    $lngE   =  180;
    $i=0;
    $hash = "";
    $error = 180;
    while($error>=$p) {
      $chr = 0;
      for($b=4;$b>=0;--$b) {
        if((1&$b) == (1&$i)) { // even char, even bit OR odd char, odd bit...a lng
          $next = ($minlng+$maxlng)/2;
          if($lng>$next) {
            $chr |= pow(2,$b);
            $minlng = $next;
          } else {
            $maxlng = $next;
          }
          $lngE /= 2;
        } else { // odd char, even bit OR even char, odd bit...a lat
          $next = ($minlat+$maxlat)/2;
          if($lat>$next) {
            $chr |= pow(2,$b);
            $minlat = $next;
          } else {
            $maxlat = $next;
          }
          $latE /= 2;
        }
      }
      $hash .= $table[$chr];
      $i++;
      $error = min($latE,$lngE);
    }
    return $hash;
  }
  
  private function parseHash() {
    $table = "0123456789bcdefghjkmnpqrstuvwxyz";
    $hash = $this->hash;
    $this->clearCoords();
    $minlat =  -90;
    $maxlat =   90;
    $minlng = -180;
    $maxlng =  180;
    $latE   =   90;
    $lngE   =  180;
    for($i=0,$c=strlen($hash);$i<$c;$i++) {
      $v = strpos($table,$hash[$i]);
      if(1&$i) {
        if(16&$v)$minlat = ($minlat+$maxlat)/2; else $maxlat = ($minlat+$maxlat)/2;
        if(8&$v) $minlng = ($minlng+$maxlng)/2; else $maxlng = ($minlng+$maxlng)/2;
        if(4&$v) $minlat = ($minlat+$maxlat)/2; else $maxlat = ($minlat+$maxlat)/2;
        if(2&$v) $minlng = ($minlng+$maxlng)/2; else $maxlng = ($minlng+$maxlng)/2;
        if(1&$v) $minlat = ($minlat+$maxlat)/2; else $maxlat = ($minlat+$maxlat)/2;
        $latE /= 8;
        $lngE /= 4;
      } else {
        if(16&$v)$minlng = ($minlng+$maxlng)/2; else $maxlng = ($minlng+$maxlng)/2;
        if(8&$v) $minlat = ($minlat+$maxlat)/2; else $maxlat = ($minlat+$maxlat)/2;
        if(4&$v) $minlng = ($minlng+$maxlng)/2; else $maxlng = ($minlng+$maxlng)/2;
        if(2&$v) $minlat = ($minlat+$maxlat)/2; else $maxlat = ($minlat+$maxlat)/2;
        if(1&$v) $minlng = ($minlng+$maxlng)/2; else $maxlng = ($minlng+$maxlng)/2;
        $latE /= 4;
        $lngE /= 8;
      }
    }
    $this->latitude  = round(($minlat+$maxlat)/2, max(1, -round(log10($latE)))-1);
    $this->longitude = round(($minlng+$maxlng)/2, max(1, -round(log10($lngE)))-1);
    $this->precision = max($latE,$lngE);
  }

}