geo_hash.php

#!/usr/bin/php
<?php

define("BASE32", "0123456789bcdefghjkmnpqrstuvwxyz");

function geo_hash_decode($geo_hash) {
  $ones_and_zeros = array_map("chr2bin", str_split($geo_hash, 1));
  $exploded = str_split(join($ones_and_zeros, ""), 1);

  $l_l = array(0 => array(), 1 => array());
  foreach($exploded as $i => $o) { 
    $l_l[$i % 2][] = $o;
  }
  
  $lon = array2val($l_l[0], 180);
  $lat = array2val($l_l[1], 90);
  
  return(array("latitude" => $lat, "longitude" => $lon));
}

function chr2bin($chr) {
  $base32 = str_split(BASE32, 1);
  $pos = array_search($chr, $base32);
  return sprintf("%05b", $pos);
}

function bin2char($bin) {
  $base32 = str_split(BASE32, 1);
  return $base32[bindec($bin)];
}

function array2val($array, $error) {
  $val = 0;
  $min = $error * -1;
  $max = $error;
  
  foreach ($array as $m) {
    ($m==0) ? $max = $val : $min = $val;
    $val = $min + abs($max - $min) / 2;
    //echo "min$min max:$max val:$val\n";
  }
  
  return $val;
}

function geo_hash_encode($lat, $lon, $precision = 12) {
  if ($precision > 12) { $precision = 12; }
  if ($precision < 1) { $precision = 1; }

  $string = "";
  $final = "";
  
  $b_lat = val2bin($lat, 90);
  $b_lon = val2bin($lon, 180);
  
  for ($i = 0; $i < max(sizeof($b_lat), sizeof($b_lon)); $i++) {
    $string .= $b_lon[$i] . $b_lat[$i];
  }
  
  foreach(str_split($string, 5) as $chunk) {
    //echo "doing $chunk\n";
    $final .= bin2char($chunk);
  }
  
  return substr($final, 0, $precision);
}

function val2bin($target, $error) {
  $val = 0;
  $min = $error * -1;
  $max = $error;
  $moves = array();

  while ($i++ <= 30) {
    if ($target > $val) {
      $moves[] = 1;
      $min = $val;
    }
    else {
      $moves[] = 0;
      $max = $val;
    }
    $val = $min + ($max - $min) / 2;
  }
  
  return $moves;
}

// val2bin(-5.60302734375, 180);

// geo_hash_decode("ezs42");
// echo "\n";
// 
// geo_hash_decode("ezs4");
// echo "\n";
// 
// geo_hash_decode("ezs");
// echo "\n";
// 
// geo_hash_decode("e");
// echo "\n";
// geo_hash_decode("dpkpdcs81jpy");
// 

//geo_hash_encode(42.6049804688, -5.60302734375);
//geo_hash_decode("ezs42ebpbpbm");

$c = "ezefd36yxyrb";
$c = "6gkzwgjzn820";
echo $c . "\n";
$g = geo_hash_decode($c);
var_dump($g);
echo geo_hash_encode($g["latitude"], $g["longitude"]);

?>