Port of GlobalMercator from python to php

GlobalMercator.php

<?php
###############################################################################
# Project:	GDAL2Tiles, Google Summer of Code 2007 & 2008
#           Global Map Tiles Classes
# Purpose:	Convert a raster into TMS tiles, create KML SuperOverlay EPSG:4326,
#			generate a simple HTML viewers based on Google Maps and OpenLayers
# Author:	Klokan Petr Pridal, klokan at klokan dot cz
# Web:		http://www.klokan.cz/projects/gdal2tiles/
#
###############################################################################
# Copyright (c) 2008 Klokan Petr Pridal. All rights reserved.
#
# Permission is hereby granted, free of charge, to any person obtaining a
# copy of this software and associated documentation files (the "Software"),
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# the rights to use, copy, modify, merge, publish, distribute, sublicense,
# and/or sell copies of the Software, and to permit persons to whom the
# Software is furnished to do so, subject to the following conditions:
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# The above copyright notice and this permission notice shall be included
# in all copies or substantial portions of the Software.
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
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###############################################################################

/**
  """
  TMS Global Mercator Profile
  ---------------------------

  Functions necessary for generation of tiles in Spherical Mercator projection,
  EPSG:900913 (EPSG:gOOglE, Google Maps Global Mercator), EPSG:3785, OSGEO:41001.

  Such tiles are compatible with Google Maps, Microsoft Virtual Earth, Yahoo Maps,
  UK Ordnance Survey OpenSpace API, ...
  and you can overlay them on top of base maps of those web mapping applications.

  Pixel and tile coordinates are in TMS notation (origin [0,0] in bottom-left).

  What coordinate conversions do we need for TMS Global Mercator tiles::

       LatLon      <->       Meters      <->     Pixels    <->       Tile

   WGS84 coordinates   Spherical Mercator  Pixels in pyramid  Tiles in pyramid
       lat/lon            XY in metres     XY pixels Z zoom      XYZ from TMS
      EPSG:4326           EPSG:900913
       .----.              ---------               --                TMS
      /      \     <->     |       |     <->     /----/    <->      Google
      \      /             |       |           /--------/          QuadTree
       -----               ---------         /------------/
     KML, public         WebMapService         Web Clients      TileMapService

  What is the coordinate extent of Earth in EPSG:900913?

    [-20037508.342789244, -20037508.342789244, 20037508.342789244, 20037508.342789244]
    Constant 20037508.342789244 comes from the circumference of the Earth in meters,
    which is 40 thousand kilometers, the coordinate origin is in the middle of extent.
      In fact you can calculate the constant as: 2 * math.pi * 6378137 / 2.0
    $ echo 180 85 | gdaltransform -s_srs EPSG:4326 -t_srs EPSG:900913
    Polar areas with abs(latitude) bigger then 85.05112878 are clipped off.

  What are zoom level constants (pixels/meter) for pyramid with EPSG:900913?

    whole region is on top of pyramid (zoom=0) covered by 256x256 pixels tile,
    every lower zoom level resolution is always divided by two
    initialResolution = 20037508.342789244 * 2 / 256 = 156543.03392804062

  What is the difference between TMS and Google Maps/QuadTree tile name convention?

    The tile raster itself is the same (equal extent, projection, pixel size),
    there is just different identification of the same raster tile.
    Tiles in TMS are counted from [0,0] in the bottom-left corner, id is XYZ.
    Google placed the origin [0,0] to the top-left corner, reference is XYZ.
    Microsoft is referencing tiles by a QuadTree name, defined on the website:
    http://msdn2.microsoft.com/en-us/library/bb259689.aspx

  The lat/lon coordinates are using WGS84 datum, yeh?

    Yes, all lat/lon we are mentioning should use WGS84 Geodetic Datum.
    Well, the web clients like Google Maps are projecting those coordinates by
    Spherical Mercator, so in fact lat/lon coordinates on sphere are treated as if
    the were on the WGS84 ellipsoid.

    From MSDN documentation:
    To simplify the calculations, we use the spherical form of projection, not
    the ellipsoidal form. Since the projection is used only for map display,
    and not for displaying numeric coordinates, we don't need the extra precision
    of an ellipsoidal projection. The spherical projection causes approximately
    0.33 percent scale distortion in the Y direction, which is not visually noticable.

  How do I create a raster in EPSG:900913 and convert coordinates with PROJ.4?

    You can use standard GIS tools like gdalwarp, cs2cs or gdaltransform.
    All of the tools supports -t_srs 'epsg:900913'.

    For other GIS programs check the exact definition of the projection:
    More info at http://spatialreference.org/ref/user/google-projection/
    The same projection is degined as EPSG:3785. WKT definition is in the official
    EPSG database.

    Proj4 Text:
      +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0
      +k=1.0 +units=m +nadgrids=@null +no_defs

    Human readable WKT format of EPGS:900913:
       PROJCS["Google Maps Global Mercator",
           GEOGCS["WGS 84",
               DATUM["WGS_1984",
                   SPHEROID["WGS 84",6378137,298.2572235630016,
                       AUTHORITY["EPSG","7030"]],
                   AUTHORITY["EPSG","6326"]],
               PRIMEM["Greenwich",0],
               UNIT["degree",0.0174532925199433],
               AUTHORITY["EPSG","4326"]],
           PROJECTION["Mercator_1SP"],
           PARAMETER["central_meridian",0],
           PARAMETER["scale_factor",1],
           PARAMETER["false_easting",0],
           PARAMETER["false_northing",0],
           UNIT["metre",1,
               AUTHORITY["EPSG","9001"]]]
  """
**/


class GlobalMercator {
  function __construct($tileSize = 256) {
    $this->tileSize = $tileSize;
    $this->initialResolution = 2 * pi() * 6378137 / $this->tileSize;
    # 156543.03392804062 for tileSize 256 pixels
    $this->originShift = 2 * pi() * 6378137 / 2.0;
   	# 20037508.342789244
  }

  /**
   * Converts given lat/lon in WGS84 Datum to XY in Spherical Mercator EPSG:900913
   * @param $lat
   * @param $lon
   * @return array
   */
  function LatLonToMeters($lat, $lon) {
    $mx = $lon * $this->originShift / 180.0;
    $my = log(tan((90 +$lat) * pi() / 360.0 )) / (pi() / 180.0);

    $my = $my * $this->originShift / 180.0;

    return array($mx, $my);
  }

  /**
   * Converts XY point from Spherical Mercator EPSG:900913 to lat/lon in WGS84 Datum
   * @param $mx
   * @param $my
   * @return array
   */
  function MetersToLatLon($mx, $my) {
    $lon = ($mx / $this->originShift) * 180.0;
    $lat = ($my / $this->originShift) * 180.0;

    $lat = 180 / pi() * (2 * atan( exp( $lat * pi() / 180.0)) - pi() / 2.0);
    return array($lat, $lon);
  }

  /**
   * Converts pixel coordinates in given zoom level of pyramid to EPSG:900913
   * @param $px
   * @param $py
   * @param $zoom
   * @return array
   */
  function PixelsToMeters($px, $py, $zoom) {
    $res = $this->Resolution( $zoom );
   	$mx = $px * $res - $this->originShift;
   	$my = $py * $res - $this->originShift;
   	return array($mx, $my);
  }

  /**
   * Converts EPSG:900913 to pyramid pixel coordinates in given zoom level
   * @param $mx
   * @param $my
   * @param $zoom
   * @return array
   */
  function MetersToPixels($mx, $my, $zoom) {
    $res = $this->Resolution( $zoom );
   	$px = ($mx + $this->originShift) / $res;
   	$py = ($my + $this->originShift) / $res;
   	return array($px, $py);
  }

  /**
   * Returns a tile covering region in given pixel coordinates
   * @param $px
   * @param $py
   * @return array
   */
  function PixelsToTile($px, $py) {
    $tx = intval( ceil( $px / floatval($this->tileSize) ) - 1 );
   	$ty = intval( ceil( $py / floatval($this->tileSize) ) - 1 );
   	return array($tx, $ty);
  }

  /**
   * Move the origin of pixel coordinates to top-left corner
   * @param $px
   * @param $py
   * @param $zoom
   * @return array
   */
  function PixelsToRaster($px, $py, $zoom) {
    $mapSize = $this->tileSize << $zoom;
   	return array($px, $mapSize - $py);
  }

  /**
   * Returns tile for given mercator coordinates
   * @param $mx
   * @param $my
   * @param $zoom
   * @return array
   */
  function MetersToTile($mx, $my, $zoom) {
    list($px, $py) = $this->MetersToPixels( $mx, $my, $zoom);
   	return $this->PixelsToTile( $px, $py);
  }

  /**
   * Returns bounds of the given tile in EPSG:900913 coordinates
   * @param $tx
   * @param $ty
   * @param $zoom
   * @return array
   */
  function TileBounds($tx, $ty, $zoom) {
    list($minx, $miny) = $this->PixelsToMeters( $tx*$this->tileSize, $ty*$this->tileSize, $zoom );
    list($maxx, $maxy) = $this->PixelsToMeters( ($tx+1)*$this->tileSize, ($ty+1)*$this->tileSize, $zoom );
   	return array( $minx, $miny, $maxx, $maxy );
  }

  /**
   * Resolution (meters/pixel) for given zoom level (measured at Equator)
   * @param $zoom
   * @return float
   */
  function Resolution( $zoom ) {
    # return (2 * math.pi * 6378137) / (self.tileSize * 2**zoom)
    return $this->initialResolution / pow(2, $zoom);
  }

  /**
   * Returns bounds of the given tile in latutude/longitude using WGS84 datum
   * @param $tx
   * @param $ty
   * @param $zoom
   * @return array
   */
  function TileLatLonBounds($tx, $ty, $zoom ) {
    $bounds = $this->TileBounds( $tx, $ty, $zoom);
    list($minLat, $minLon) = $this->MetersToLatLon($bounds[0], $bounds[1]);
    list($maxLat, $maxLon) = $this->MetersToLatLon($bounds[2], $bounds[3]);

   	return array( $minLat, $minLon, $maxLat, $maxLon );
  }

  /**
   * Maximal scaledown zoom of the pyramid closest to the pixelSize.
   * @param $pixelSize
   * @return int
   */
  function ZoomForPixelSize($pixelSize) {
    foreach (range(0, 30) as $i) {
      if ($pixelSize > $this->Resolution($i)) {
        return $i != 0 ? $i - 1 : 0; # We don't want to scale up
      }
    }
  }

  /**
   * Converts TMS tile coordinates to Google Tile coordinates
   * @param $tx
   * @param $ty
   * @param $zoom
   * @return array
   */
  function GoogleTile($tx, $ty, $zoom) {
  	# coordinate origin is moved from bottom-left to top-left corner of the extent
    return array($tx, (pow(2, $zoom) - 1) - $ty);
  }
}