Bing maps: create url and determining best map view for an array of locations

map_view.php

<?php
  // https://rbrundritt.wordpress.com/2009/07/21/determining-best-map-view-for-an-array-of-locations/
  // Calculates the best map view for a list of locations for a map
  // 
  // locations = List of location objects
  // map_width = Map width in pixels
  // map_height = Map height in pixels
  // buffer = Width in pixels to use to create a buffer around the map. This is to keep pushpins from being cut off on the edge
  // 
  // Returns a MapViewSpecification with the best map center point and zoom level for the given set of locations
  public function get_map_view($locations, $map_width = 500, $map_height = 500, $buffer = 50)
  {
    $center = array('lat' => 0, 'lng' => 0);
    $zoom_level = 1; // 1-19

    $max_lat =  -85;
    $min_lat =   85;
    $max_lng = -180;
    $min_lng =  180;

    // calculate bounding rectangle
    for ($i = 0; $i < count($locations); $i++)
    {
      if ($locations[ $i ]['lat'] > $max_lat) $max_lat = $locations[ $i ]['lat'];
      if ($locations[ $i ]['lat'] < $min_lat) $min_lat = $locations[ $i ]['lat'];

      if ($locations[ $i ]['lng'] > $max_lng) $max_lng = $locations[ $i ]['lng'];
      if ($locations[ $i ]['lng'] < $min_lng) $min_lng = $locations[ $i ]['lng'];
    }

    $center['lat'] = ($max_lat + $min_lat) / 2;
    $center['lng'] = ($max_lng + $min_lng) / 2;

    $zoom_w = 0; $zoom_h = 0;

    // https://msdn.microsoft.com/en-us/library/bb259689.aspx
    // map width = map height = 256 * 2 ^ level pixels
    
    // Determine the best zoom level based on the map scale and bounding coordinate information
    if ($max_lng != $min_lng && $max_lat != $min_lat)
    {
      // best zoom level based on map width
      $zoom_w = log(360 / 256 * ($map_width - (2*$buffer) ) / ($max_lng - $min_lng)) / log(2);
      // best zoom level based on map height
      $zoom_h = log(180 / 256 * ($map_height - (2*$buffer) ) / ($max_lat - $min_lat)) / log(2);
    }

    // use the most zoomed out of the two zoom levels
    $zoom_level = floor( min($zoom_w, $zoom_h) );

    // An integer between 0 and 21.
    $zoom_level = max($zoom_level,  1);
    $zoom_level = min($zoom_level, 19);

    $map_view['center'] = $center;
    $map_view['zoom_level'] = $zoom_level;

    return $map_view;
  }

  public function build_url($locations, $format)
  {
    $map_view = $this->get_map_view($locations);

    $this->CI->load->config('api_key', TRUE);
    $map_key = $this->CI->config->item('bing_public', 'api_key');

    // https://msdn.microsoft.com/en-in/library/ff701724.aspx
    $path = array(
      'type'        => 'REST',
      'version'     => 'v1',
      'imagery'     => 'Imagery',
      'map'         => 'Map',
      'imagerySet'  => 'Road',
      
      'centerPoint' => $map_view['center']['lat'].','.$map_view['center']['lng'], // '0,0'
      'zoomLevel'   => $map_view['zoom_level'], // An integer between 0 and 21.
    );
    $query = array(
      'mapSize'   => '500,500',
      'key'       => $map_key,

      // Pushpin Syntax and Icon Styles
      // https://msdn.microsoft.com/en-in/library/ff701719.aspx
      // pushpin=latitude,longitude;iconStyle;label
      // 'pp'        => '0,0;37;',

      // declutterPins=0 [default]
      'dcl'       => '1',

      'format'    => $format,
    );

    $pp_query = '';
    if (!empty($locations)) foreach ($locations as  $loaction)
    {
      $pp_query .= '&'.'pp='.$loaction['lat'].','.$loaction['lng'].';37;';
    }

    $url = 'http://dev.virtualearth.net/'.implode('/', $path).'?'.http_build_query($query).$pp_query;

    return $url;
  }