function MarkerManager(map, opt_opts) {
  var me = this;
  me.map_ = map;
  me.mapZoom_ = map.getZoom();
  me.projection_ = map.getCurrentMapType().getProjection();

  opt_opts = opt_opts || {};
  me.tileSize_ = MarkerManager.DEFAULT_TILE_SIZE_;
  
  var maxZoom = MarkerManager.DEFAULT_MAX_ZOOM_;
  if(opt_opts.maxZoom != undefined) {
    maxZoom = opt_opts.maxZoom;
  }
  me.maxZoom_ = maxZoom;

  me.trackMarkers_ = opt_opts.trackMarkers;

  var padding;
  if (typeof opt_opts.borderPadding == "number") {
    padding = opt_opts.borderPadding;
  } else {
    padding = MarkerManager.DEFAULT_BORDER_PADDING_;
  }
  me.swPadding_ = new GSize(-padding, padding);
  me.nePadding_ = new GSize(padding, -padding);
  me.borderPadding_ = padding;

  me.gridWidth_ = [];

  me.grid_ = [];
  me.grid_[maxZoom] = [];
  me.numMarkers_ = [];
  me.numMarkers_[maxZoom] = 0;

  GEvent.bind(map, "moveend", me, me.onMapMoveEnd_);

  me.removeOverlay_ = function(marker) {
    if (!marker.isInfoWindowOpened) {
      map.removeOverlay(marker);
      me.shownMarkers_--;
    }
  };
  me.addOverlay_ = function(marker) {
    if (!marker.isInfoWindowOpened) {
      marker.isInfoWindowOpened = false;
      map.addOverlay(marker);
      me.shownMarkers_++;
    }
  };

  me.resetManager_();
  me.shownMarkers_ = 0;

  me.shownBounds_ = me.getMapGridBounds_();
};

MarkerManager.DEFAULT_TILE_SIZE_ = 1024;
MarkerManager.DEFAULT_MAX_ZOOM_ = 17;
MarkerManager.DEFAULT_BORDER_PADDING_ = 100;
MarkerManager.MERCATOR_ZOOM_LEVEL_ZERO_RANGE = 256;


MarkerManager.prototype.resetManager_ = function() {
  var me = this;
  var mapWidth = MarkerManager.MERCATOR_ZOOM_LEVEL_ZERO_RANGE;
  for (var zoom = 0; zoom <= me.maxZoom_; ++zoom) {
    me.grid_[zoom] = [];
    me.numMarkers_[zoom] = 0;
    me.gridWidth_[zoom] = Math.ceil(mapWidth/me.tileSize_);
    mapWidth <<= 1;
  }
};

MarkerManager.prototype.clearMarkers = function() {
  var me = this;
  me.processAll_(me.shownBounds_, me.removeOverlay_);
  me.resetManager_();
};


/**
 * Gets the tile coordinate for a given latlng point.
 *
 * @param {LatLng} latlng The geographical point.
 * @param {Number} zoom The zoom level.
 * @param {GSize} padding The padding used to shift the pixel coordinate.
 *               Used for expanding a bounds to include an extra padding
 *               of pixels surrounding the bounds.
 * @return {GPoint} The point in tile coordinates.
 *
 */
MarkerManager.prototype.getTilePoint_ = function(latlng, zoom, padding) {
  var pixelPoint = this.projection_.fromLatLngToPixel(latlng, zoom);
  return new GPoint(
      Math.floor((pixelPoint.x + padding.width) / this.tileSize_),
      Math.floor((pixelPoint.y + padding.height) / this.tileSize_));
};


/**
 * Finds the appropriate place to add the marker to the grid.
 * Optimized for speed; does not actually add the marker to the map.
 * Designed for batch-processing thousands of markers.
 *
 * @param {Marker} marker The marker to add.
 * @param {Number} minZoom The minimum zoom for displaying the marker.
 * @param {Number} maxZoom The maximum zoom for displaying the marker.
 */
MarkerManager.prototype.addMarkerBatch_ = function(marker, minZoom, maxZoom) {
  var mPoint = marker.getPoint();
  // Tracking markers is expensive, so we do this only if the
  // user explicitly requested it when creating marker manager.
  if (this.trackMarkers_) {
    GEvent.bind(marker, "changed", this, this.onMarkerMoved_);
  }

  GEvent.addListener(marker, "infowindowopen", function() {
    marker.isInfoWindowOpened = true;
  });

  GEvent.addListener(marker, "infowindowclose", function() {
    marker.isInfoWindowOpened = false;
  });

  var gridPoint = this.getTilePoint_(mPoint, maxZoom, GSize.ZERO);

  for (var zoom = maxZoom; zoom >= minZoom; zoom--) {
    var cell = this.getGridCellCreate_(gridPoint.x, gridPoint.y, zoom);
    cell.push(marker);

    gridPoint.x = gridPoint.x >> 1;
    gridPoint.y = gridPoint.y >> 1;
  }
};


/**
 * Returns whether or not the given point is visible in the shown bounds. This
 * is a helper method that takes care of the corner case, when shownBounds have
 * negative minX value.
 *
 * @param {Point} point a point on a grid.
 * @return {Boolean} Whether or not the given point is visible in the currently
 * shown bounds.
 */
MarkerManager.prototype.isGridPointVisible_ = function(point) {
  var me = this;
  var vertical = me.shownBounds_.minY <= point.y &&
      point.y <= me.shownBounds_.maxY;
  var minX = me.shownBounds_.minX;
  var horizontal = minX <= point.x && point.x <= me.shownBounds_.maxX;
  if (!horizontal && minX < 0) {
    // Shifts the negative part of the rectangle. As point.x is always less
    // than grid width, only test shifted minX .. 0 part of the shown bounds.
    var width = me.gridWidth_[me.shownBounds_.z];
    horizontal = minX + width <= point.x && point.x <= width - 1;
  }
  return vertical && horizontal;
}


/**
 * Reacts to a notification from a marker that it has moved to a new location.
 * It scans the grid all all zoom levels and moves the marker from the old grid
 * location to a new grid location.
 *
 * @param {Marker} marker The marker that moved.
 * @param {LatLng} oldPoint The old position of the marker.
 * @param {LatLng} newPoint The new position of the marker.
 */
MarkerManager.prototype.onMarkerMoved_ = function(marker, oldPoint, newPoint) {
  // NOTE: We do not know the minimum or maximum zoom the marker was
  // added at, so we start at the absolute maximum. Whenever we successfully
  // remove a marker at a given zoom, we add it at the new grid coordinates.
  var me = this;
  var zoom = me.maxZoom_;
  var changed = false;
  var oldGrid = me.getTilePoint_(oldPoint, zoom, GSize.ZERO);
  var newGrid = me.getTilePoint_(newPoint, zoom, GSize.ZERO);
  while (zoom >= 0 && (oldGrid.x != newGrid.x || oldGrid.y != newGrid.y)) {
    var cell = me.getGridCellNoCreate_(oldGrid.x, oldGrid.y, zoom);
    if (cell) {
      if (me.removeFromArray(cell, marker)) {
        me.getGridCellCreate_(newGrid.x, newGrid.y, zoom).push(marker);
      }
    }
    // For the current zoom we also need to update the map. Markers that no
    // longer are visible are removed from the map. Markers that moved into
    // the shown bounds are added to the map. This also lets us keep the count
    // of visible markers up to date.
    if (zoom == me.mapZoom_) {
      if (me.isGridPointVisible_(oldGrid)) {
        if (!me.isGridPointVisible_(newGrid)) {
          me.removeOverlay_(marker);
          changed = true;
        }
      } else {
        if (me.isGridPointVisible_(newGrid)) {
          me.addOverlay_(marker);
          changed = true;
        }
      }
    }
    oldGrid.x = oldGrid.x >> 1;
    oldGrid.y = oldGrid.y >> 1;
    newGrid.x = newGrid.x >> 1;
    newGrid.y = newGrid.y >> 1;
    --zoom;
  }
  if (changed) {
    me.notifyListeners_();
  }
};


/**
 * Searches at every zoom level to find grid cell
 * that marker would be in, removes from that array if found.
 * Also removes marker with removeOverlay if visible.
 * @param {GMarker} marker The marker to delete.
 */
MarkerManager.prototype.removeMarker = function(marker) {
  var me = this;
  var zoom = me.maxZoom_;
  var changed = false;
  var point = marker.getPoint();
  var grid = me.getTilePoint_(point, zoom, GSize.ZERO);
  while (zoom >= 0) {
    var cell = me.getGridCellNoCreate_(grid.x, grid.y, zoom);

    if (cell) {
      me.removeFromArray(cell, marker);
    }
    // For the current zoom we also need to update the map. Markers that no
    // longer are visible are removed from the map. This also lets us keep the count
    // of visible markers up to date.
    if (zoom == me.mapZoom_) {
      if (me.isGridPointVisible_(grid)) {
          me.removeOverlay_(marker);
          changed = true;
      } 
    }
    grid.x = grid.x >> 1;
    grid.y = grid.y >> 1;
    --zoom;
  }
  if (changed) {
    me.notifyListeners_();
  }
};


/**
 * Add many markers at once.
 * Does not actually update the map, just the internal grid.
 *
 * @param {Array of Marker} markers The markers to add.
 * @param {Number} minZoom The minimum zoom level to display the markers.
 * @param {Number} opt_maxZoom The maximum zoom level to display the markers.
 */
MarkerManager.prototype.addMarkers = function(markers, minZoom, opt_maxZoom) {
  var maxZoom = this.getOptMaxZoom_(opt_maxZoom);
  for (var i = markers.length - 1; i >= 0; i--) {
    this.addMarkerBatch_(markers[i], minZoom, maxZoom);
  }

  this.numMarkers_[minZoom] += markers.length;
};


/**
 * Returns the value of the optional maximum zoom. This method is defined so
 * that we have just one place where optional maximum zoom is calculated.
 *
 * @param {Number} opt_maxZoom The optinal maximum zoom.
 * @return The maximum zoom.
 */
MarkerManager.prototype.getOptMaxZoom_ = function(opt_maxZoom) {
  return opt_maxZoom != undefined ? opt_maxZoom : this.maxZoom_;
}


/**
 * Calculates the total number of markers potentially visible at a given
 * zoom level.
 *
 * @param {Number} zoom The zoom level to check.
 */
MarkerManager.prototype.getMarkerCount = function(zoom) {
  var total = 0;
  for (var z = 0; z <= zoom; z++) {
    total += this.numMarkers_[z];
  }
  return total;
};


/**
 * Add a single marker to the map.
 *
 * @param {Marker} marker The marker to add.
 * @param {Number} minZoom The minimum zoom level to display the marker.
 * @param {Number} opt_maxZoom The maximum zoom level to display the marker.
 */
MarkerManager.prototype.addMarker = function(marker, minZoom, opt_maxZoom) {
  var me = this;
  var maxZoom = this.getOptMaxZoom_(opt_maxZoom);
  me.addMarkerBatch_(marker, minZoom, maxZoom);
  var gridPoint = me.getTilePoint_(marker.getPoint(), me.mapZoom_, GSize.ZERO);
  if(me.isGridPointVisible_(gridPoint) && 
     minZoom <= me.shownBounds_.z &&
     me.shownBounds_.z <= maxZoom ) {
    me.addOverlay_(marker);
    me.notifyListeners_();
  }
  this.numMarkers_[minZoom]++;
};

/**
 * Returns true if this bounds (inclusively) contains the given point.
 * @param {Point} point  The point to test.
 * @return {Boolean} This Bounds contains the given Point.
 */
GBounds.prototype.containsPoint = function(point) {
  var outer = this;
  return (outer.minX <= point.x &&
          outer.maxX >= point.x &&
          outer.minY <= point.y &&
          outer.maxY >= point.y);
}

/**
 * Get a cell in the grid, creating it first if necessary.
 *
 * Optimization candidate
 *
 * @param {Number} x The x coordinate of the cell.
 * @param {Number} y The y coordinate of the cell.
 * @param {Number} z The z coordinate of the cell.
 * @return {Array} The cell in the array.
 */
MarkerManager.prototype.getGridCellCreate_ = function(x, y, z) {
  var grid = this.grid_[z];
  if (x < 0) {
    x += this.gridWidth_[z];
  }
  var gridCol = grid[x];
  if (!gridCol) {
    gridCol = grid[x] = [];
    return gridCol[y] = [];
  }
  var gridCell = gridCol[y];
  if (!gridCell) {
    return gridCol[y] = [];
  }
  return gridCell;
};


/**
 * Get a cell in the grid, returning undefined if it does not exist.
 *
 * NOTE: Optimized for speed -- otherwise could combine with getGridCellCreate_.
 *
 * @param {Number} x The x coordinate of the cell.
 * @param {Number} y The y coordinate of the cell.
 * @param {Number} z The z coordinate of the cell.
 * @return {Array} The cell in the array.
 */
MarkerManager.prototype.getGridCellNoCreate_ = function(x, y, z) {
  var grid = this.grid_[z];
  if (x < 0) {
    x += this.gridWidth_[z];
  }
  var gridCol = grid[x];
  return gridCol ? gridCol[y] : undefined;
};


/**
 * Turns at geographical bounds into a grid-space bounds.
 *
 * @param {LatLngBounds} bounds The geographical bounds.
 * @param {Number} zoom The zoom level of the bounds.
 * @param {GSize} swPadding The padding in pixels to extend beyond the
 * given bounds.
 * @param {GSize} nePadding The padding in pixels to extend beyond the
 * given bounds.
 * @return {GBounds} The bounds in grid space.
 */
MarkerManager.prototype.getGridBounds_ = function(bounds, zoom, swPadding,
                                                  nePadding) {
  zoom = Math.min(zoom, this.maxZoom_);
  
  var bl = bounds.getSouthWest();
  var tr = bounds.getNorthEast();
  var sw = this.getTilePoint_(bl, zoom, swPadding);
  var ne = this.getTilePoint_(tr, zoom, nePadding);
  var gw = this.gridWidth_[zoom];
  
  // Crossing the prime meridian requires correction of bounds.
  if (tr.lng() < bl.lng() || ne.x < sw.x) {
    sw.x -= gw;
  }
  if (ne.x - sw.x  + 1 >= gw) {
    // Computed grid bounds are larger than the world; truncate.
    sw.x = 0;
    ne.x = gw - 1;
  }
  var gridBounds = new GBounds([sw, ne]);
  gridBounds.z = zoom;
  return gridBounds;
};


/**
 * Gets the grid-space bounds for the current map viewport.
 *
 * @return {Bounds} The bounds in grid space.
 */
MarkerManager.prototype.getMapGridBounds_ = function() {
  var me = this;
  return me.getGridBounds_(me.map_.getBounds(), me.mapZoom_,
                           me.swPadding_, me.nePadding_);
};


/**
 * Event listener for map:movend.
 * NOTE: Use a timeout so that the user is not blocked
 * from moving the map.
 *
 */
MarkerManager.prototype.onMapMoveEnd_ = function() {
  var me = this;
  me.objectSetTimeout_(this, this.updateMarkers_, 0);
};


/**
 * Call a function or evaluate an expression after a specified number of
 * milliseconds.
 *
 * Equivalent to the standard window.setTimeout function, but the given
 * function executes as a method of this instance. So the function passed to
 * objectSetTimeout can contain references to this.
 *    objectSetTimeout(this, function() { alert(this.x) }, 1000);
 *
 * @param {Object} object  The target object.
 * @param {Function} command  The command to run.
 * @param {Number} milliseconds  The delay.
 * @return {Boolean}  Success.
 */
MarkerManager.prototype.objectSetTimeout_ = function(object, command, milliseconds) {
  return window.setTimeout(function() {
    command.call(object);
  }, milliseconds);
};


/**
 * Refresh forces the marker-manager into a good state.
 * <ol>
 *   <li>If never before initialized, shows all the markers.</li>
 *   <li>If previously initialized, removes and re-adds all markers.</li>
 * </ol>
 */
MarkerManager.prototype.refresh = function() {
  var me = this;
  if (me.shownMarkers_ > 0) {
    me.processAll_(me.shownBounds_, me.removeOverlay_);
  }
  me.processAll_(me.shownBounds_, me.addOverlay_);
  me.notifyListeners_();
};


/**
 * After the viewport may have changed, add or remove markers as needed.
 */
MarkerManager.prototype.updateMarkers_ = function() {
  var me = this;
  me.mapZoom_ = this.map_.getZoom();
  var newBounds = me.getMapGridBounds_();
  
  // If the move does not include new grid sections,
  // we have no work to do:
  if (newBounds.equals(me.shownBounds_) && newBounds.z == me.shownBounds_.z) {
    return;
  }

  if (newBounds.z != me.shownBounds_.z) {
    me.processAll_(me.shownBounds_, me.removeOverlay_);
    me.processAll_(newBounds, me.addOverlay_);
  } else {
    // Remove markers:
    me.rectangleDiff_(me.shownBounds_, newBounds, me.removeCellMarkers_);

    // Add markers:
    me.rectangleDiff_(newBounds, me.shownBounds_, me.addCellMarkers_);
  }
  me.shownBounds_ = newBounds;

  me.notifyListeners_();
};


/**
 * Notify listeners when the state of what is displayed changes.
 */
MarkerManager.prototype.notifyListeners_ = function() {
  GEvent.trigger(this, "changed", this.shownBounds_, this.shownMarkers_);
};


/**
 * Process all markers in the bounds provided, using a callback.
 *
 * @param {Bounds} bounds The bounds in grid space.
 * @param {Function} callback The function to call for each marker.
 */
MarkerManager.prototype.processAll_ = function(bounds, callback) {
  for (var x = bounds.minX; x <= bounds.maxX; x++) {
    for (var y = bounds.minY; y <= bounds.maxY; y++) {
      this.processCellMarkers_(x, y,  bounds.z, callback);
    }
  }
};


/**
 * Process all markers in the grid cell, using a callback.
 *
 * @param {Number} x The x coordinate of the cell.
 * @param {Number} y The y coordinate of the cell.
 * @param {Number} z The z coordinate of the cell.
 * @param {Function} callback The function to call for each marker.
 */
MarkerManager.prototype.processCellMarkers_ = function(x, y, z, callback) {
  var cell = this.getGridCellNoCreate_(x, y, z);
  if (cell) {
    for (var i = cell.length - 1; i >= 0; i--) {
      callback(cell[i]);
    }
  }
};


/**
 * Remove all markers in a grid cell.
 *
 * @param {Number} x The x coordinate of the cell.
 * @param {Number} y The y coordinate of the cell.
 * @param {Number} z The z coordinate of the cell.
 */
MarkerManager.prototype.removeCellMarkers_ = function(x, y, z) {
  this.processCellMarkers_(x, y, z, this.removeOverlay_);
};


/**
 * Add all markers in a grid cell.
 *
 * @param {Number} x The x coordinate of the cell.
 * @param {Number} y The y coordinate of the cell.
 * @param {Number} z The z coordinate of the cell.
 */
MarkerManager.prototype.addCellMarkers_ = function(x, y, z) {
  this.processCellMarkers_(x, y, z, this.addOverlay_);
};


/**
 * Use the rectangleDiffCoords function to process all grid cells
 * that are in bounds1 but not bounds2, using a callback, and using
 * the current MarkerManager object as the instance.
 *
 * Pass the z parameter to the callback in addition to x and y.
 *
 * @param {Bounds} bounds1 The bounds of all points we may process.
 * @param {Bounds} bounds2 The bounds of points to exclude.
 * @param {Function} callback The callback function to call
 *                   for each grid coordinate (x, y, z).
 */
MarkerManager.prototype.rectangleDiff_ = function(bounds1, bounds2, callback) {
  var me = this;
  me.rectangleDiffCoords(bounds1, bounds2, function(x, y) {
    callback.apply(me, [x, y, bounds1.z]);
  });
};


/**
 * Calls the function for all points in bounds1, not in bounds2
 *
 * @param {Bounds} bounds1 The bounds of all points we may process.
 * @param {Bounds} bounds2 The bounds of points to exclude.
 * @param {Function} callback The callback function to call
 *                   for each grid coordinate.
 */
MarkerManager.prototype.rectangleDiffCoords = function(bounds1, bounds2, callback) {
  var minX1 = bounds1.minX;
  var minY1 = bounds1.minY;
  var maxX1 = bounds1.maxX;
  var maxY1 = bounds1.maxY;
  var minX2 = bounds2.minX;
  var minY2 = bounds2.minY;
  var maxX2 = bounds2.maxX;
  var maxY2 = bounds2.maxY;

  for (var x = minX1; x <= maxX1; x++) {  // All x in R1
    // All above:
    for (var y = minY1; y <= maxY1 && y < minY2; y++) {  // y in R1 above R2
      callback(x, y);
    }
    // All below:
    for (var y = Math.max(maxY2 + 1, minY1);  // y in R1 below R2
         y <= maxY1; y++) {
      callback(x, y);
    }
  }

  for (var y = Math.max(minY1, minY2);
       y <= Math.min(maxY1, maxY2); y++) {  // All y in R2 and in R1
    // Strictly left:
    for (var x = Math.min(maxX1 + 1, minX2) - 1;
         x >= minX1; x--) {  // x in R1 left of R2
      callback(x, y);
    }
    // Strictly right:
    for (var x = Math.max(minX1, maxX2 + 1);  // x in R1 right of R2
         x <= maxX1; x++) {
      callback(x, y);
    }
  }
};


/**
 * Removes value from array. O(N).
 *
 * @param {Array} array  The array to modify.
 * @param {any} value  The value to remove.
 * @param {Boolean} opt_notype  Flag to disable type checking in equality.
 * @return {Number}  The number of instances of value that were removed.
 */
MarkerManager.prototype.removeFromArray = function(array, value, opt_notype) {
  var shift = 0;
  for (var i = 0; i < array.length; ++i) {
    if (array[i] === value || (opt_notype && array[i] == value)) {
      array.splice(i--, 1);
      shift++;
    }
  }
  return shift;
};