/* Copyright (c) 2006-2010 by OpenLayers Contributors (see authors.txt for
* full list of contributors). Published under the Clear BSD license.
* See http://svn.openlayers.org/trunk/openlayers/license.txt for the
* full text of the license. */
/**
* @requires OpenLayers/Layer.js
* @requires OpenLayers/Projection.js
*/
/**
* Class: OpenLayers.Layer.SphericalMercator
* A mixin for layers that wraps up the pieces neccesary to have a coordinate
* conversion for working with commercial APIs which use a spherical
* mercator projection. Using this layer as a base layer, additional
* layers can be used as overlays if they are in the same projection.
*
* A layer is given properties of this object by setting the sphericalMercator
* property to true.
*
* More projection information:
* - http://spatialreference.org/ref/user/google-projection/
*
* 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
*
* WKT:
* 900913=PROJCS["WGS84 / Simple Mercator", GEOGCS["WGS 84",
* DATUM["WGS_1984", SPHEROID["WGS_1984", 6378137.0, 298.257223563]],
* PRIMEM["Greenwich", 0.0], UNIT["degree", 0.017453292519943295],
* AXIS["Longitude", EAST], AXIS["Latitude", NORTH]],
* PROJECTION["Mercator_1SP_Google"],
* PARAMETER["latitude_of_origin", 0.0], PARAMETER["central_meridian", 0.0],
* PARAMETER["scale_factor", 1.0], PARAMETER["false_easting", 0.0],
* PARAMETER["false_northing", 0.0], UNIT["m", 1.0], AXIS["x", EAST],
* AXIS["y", NORTH], AUTHORITY["EPSG","900913"]]
*/
OpenLayers.Layer.SphericalMercator = {
/**
* Method: getExtent
* Get the map's extent.
*
* Returns:
* {<OpenLayers.Bounds>} The map extent.
*/
getExtent: function() {
var extent = null;
if (this.sphericalMercator) {
extent = this.map.calculateBounds();
} else {
extent = OpenLayers.Layer.FixedZoomLevels.prototype.getExtent.apply(this);
}
return extent;
},
/**
* Method: getLonLatFromViewPortPx
* Get a map location from a pixel location
*
* Parameters:
* viewPortPx - {<OpenLayers.Pixel>}
*
* Returns:
* {<OpenLayers.LonLat>} An OpenLayers.LonLat which is the passed-in view
* port OpenLayers.Pixel, translated into lon/lat by map lib
* If the map lib is not loaded or not centered, returns null
*/
getLonLatFromViewPortPx: function (viewPortPx) {
return OpenLayers.Layer.prototype.getLonLatFromViewPortPx.apply(this, arguments);
},
/**
* Method: getViewPortPxFromLonLat
* Get a pixel location from a map location
*
* Parameters:
* lonlat - {<OpenLayers.LonLat>}
*
* Returns:
* {<OpenLayers.Pixel>} An OpenLayers.Pixel which is the passed-in
* OpenLayers.LonLat, translated into view port pixels by map lib
* If map lib is not loaded or not centered, returns null
*/
getViewPortPxFromLonLat: function (lonlat) {
return OpenLayers.Layer.prototype.getViewPortPxFromLonLat.apply(this, arguments);
},
/**
* Method: initMercatorParameters
* Set up the mercator parameters on the layer: resolutions,
* projection, units.
*/
initMercatorParameters: function() {
// set up properties for Mercator - assume EPSG:900913
this.RESOLUTIONS = [];
var maxResolution = 156543.0339;
for(var zoom=0; zoom<=this.MAX_ZOOM_LEVEL; ++zoom) {
this.RESOLUTIONS[zoom] = maxResolution / Math.pow(2, zoom);
}
this.units = "m";
this.projection = this.projection || "EPSG:900913";
},
/**
* APIMethod: forwardMercator
* Given a lon,lat in EPSG:4326, return a point in Spherical Mercator.
*
* Parameters:
* lon - {float}
* lat - {float}
*
* Returns:
* {<OpenLayers.LonLat>} The coordinates transformed to Mercator.
*/
forwardMercator: function(lon, lat) {
var x = lon * 20037508.34 / 180;
var y = Math.log(Math.tan((90 + lat) * Math.PI / 360)) / (Math.PI / 180);
y = y * 20037508.34 / 180;
return new OpenLayers.LonLat(x, y);
},
/**
* APIMethod: inverseMercator
* Given a x,y in Spherical Mercator, return a point in EPSG:4326.
*
* Parameters:
* x - {float} A map x in Spherical Mercator.
* y - {float} A map y in Spherical Mercator.
*
* Returns:
* {<OpenLayers.LonLat>} The coordinates transformed to EPSG:4326.
*/
inverseMercator: function(x, y) {
var lon = (x / 20037508.34) * 180;
var lat = (y / 20037508.34) * 180;
lat = 180/Math.PI * (2 * Math.atan(Math.exp(lat * Math.PI / 180)) - Math.PI / 2);
return new OpenLayers.LonLat(lon, lat);
},
/**
* Method: projectForward
* Given an object with x and y properties in EPSG:4326, modify the x,y
* properties on the object to be the Spherical Mercator projected
* coordinates.
*
* Parameters:
* point - {Object} An object with x and y properties.
*
* Returns:
* {Object} The point, with the x and y properties transformed to spherical
* mercator.
*/
projectForward: function(point) {
var lonlat = OpenLayers.Layer.SphericalMercator.forwardMercator(point.x, point.y);
point.x = lonlat.lon;
point.y = lonlat.lat;
return point;
},
/**
* Method: projectInverse
* Given an object with x and y properties in Spherical Mercator, modify
* the x,y properties on the object to be the unprojected coordinates.
*
* Parameters:
* point - {Object} An object with x and y properties.
*
* Returns:
* {Object} The point, with the x and y properties transformed from
* spherical mercator to unprojected coordinates..
*/
projectInverse: function(point) {
var lonlat = OpenLayers.Layer.SphericalMercator.inverseMercator(point.x, point.y);
point.x = lonlat.lon;
point.y = lonlat.lat;
return point;
}
};
/**
* Note: Two transforms declared
* Transforms from EPSG:4326 to EPSG:900913 and from EPSG:900913 to EPSG:4326
* are set by this class.
*/
OpenLayers.Projection.addTransform("EPSG:4326", "EPSG:900913",
OpenLayers.Layer.SphericalMercator.projectForward);
OpenLayers.Projection.addTransform("EPSG:900913", "EPSG:4326",
OpenLayers.Layer.SphericalMercator.projectInverse);