Patch minZoom/maxZoom

//--------------------------------------------------------------------------------------------------
//  $Id: OpenLayers_Map_minZoom_maxZoom_Patch.js,v 1.2 2012/02/25 11:54:36 wolf Exp wolf $
//--------------------------------------------------------------------------------------------------
//
//  class:  OpenLayers.Map
//  fields: minZoom, maxZoom
//  methods: moveTo, getNumZoomLevels
//
//--------------------------------------------------------------------------------
//
//  The Problem:
//
//  Map zoom needs to be restricted to a certain range.
//
//--------------------------------------------------------------------------------
//
//  The solution (not really):
//
//  The method Map.moveTo is patched to limit its parameter "zoom" to the
//  range defined by the Map fields "minZoom" and "maxZoom".
//
//--------------------------------------------------------------------------------
//
//  BEWARE!
//
//  The OpenLayers zoom/pan logic is based on the assumption, that zero is
//  allways a safe value for zoom. THIS PATCH SUBVERTS THIS ASSUMPTION!
//
//  There may be side effects.
//
//--------------------------------------------------------------------------------
//  http://www.netzwolf.info/kartografie/openlayers/restrictedzoom.htm
//--------------------------------------------------------------------------------

(function () {
    OpenLayers.Map.prototype.minZoom = null;
    OpenLayers.Map.prototype.maxZoom = null;

    var moveTo = OpenLayers.Map.prototype.moveTo;

    OpenLayers.Map.prototype.moveTo = function (lonlat, zoom, options) {

        if (this.minZoom && zoom<this.minZoom) {
            zoom  = this.minZoom;
            center = ol.map.getCenter();
            if (center) lonlat=center;
        }
        if (this.maxZoom && zoom>this.maxZoom) {
            zoom = this.maxZoom;
            center = ol.map.getCenter();
            if (center) lonlat=center;
        }

        return moveTo.apply (this, [lonlat, zoom, options]);
    };

    var getNumZoomLevels = OpenLayers.Map.prototype.getNumZoomLevels;

    OpenLayers.Map.prototype.getNumZoomLevels = function () {

        var num = getNumZoomLevels.apply (this, arguments);
        if (this.maxZoom && num>this.maxZoom+1) num = this.maxZoom+1;
        return num;
    };
})();

//--------------------------------------------------------------------------------------------------
//  $Id: OpenLayers_Map_minZoom_maxZoom_Patch.js,v 1.2 2012/02/25 11:54:36 wolf Exp wolf $
//--------------------------------------------------------------------------------------------------