/*

 * Call generic wms service for GoogleMaps v2

 * John Deck, UC Berkeley

 * Inspiration & Code from:

 *      Mike Williams http://www.econym.demon.co.uk/googlemaps2/ V2 Reference & custommap code

 *      Brian Flood http://www.spatialdatalogic.com/cs/blogs/brian_flood/archive/2005/07/11/39.aspx V1

 WMS code

 *      Kyle Mulka http://blog.kylemulka.com/?p=287  V1 WMS code modifications

 *      http://search.cpan.org/src/RRWO/GPS-Lowrance-0.31/lib/Geo/Coordinates/MercatorMeters.pm

 * 		Modified by Chris Holmes, TOPP to work by default with GeoServer.

 *		Guilhem Vellut <guilhem.vellut@gmail.com> for more accurate Javascript Mercator Fxn

 *

 * Note this only works with gmaps v2.36 and above.  http://johndeck.blogspot.com

 * has scripts

 * that do the same for older gmaps versions - just change from 54004 to 41001.

 *

 * About:

 * This script provides an implementation of GTileLayer that works with WMS

 * services that provide epsg 41001 (Mercator).  This provides a reasonable

 * accuracy on overlays at most zoom levels.  It switches between Mercator

 * and Lat/Long at the myMercZoomLevel variable, defaulting to MERC_ZOOM_DEFAULT

 * of 5.  It also performs the calculation from a GPoint to the appropriate

 * BBOX to pass the WMS.  The overlays could be more accurate, and if you

 * figure out a way to make them so please contribute information back to

 * http://docs.codehaus.org/display/GEOSDOC/Google+Maps.  There is much

 * information at:

 * http://cfis.savagexi.com/articles/2006/05/03/google-maps-deconstructed

 *

 * Use:

 * This script is used by creating a new GTileLayer, setting the required

 * and any desired optional variables, and setting the functions here to

 * override the appropriate GTileLayer ones.

 *

 * At the very least you will need:

 * var myTileLayer= new GTileLayer(new GCopyrightCollection(""),1,17);

 *     myTileLayer.myBaseURL='http://yourserver.org/wms?'

 *     myTileLayer.myLayers='myLayerName';

 *     myTileLayer=CustomGetTileUrl

 *

 * After that you can override the format (myFormat), the level at

 * which the zoom switches (myMercZoomLevel), and the style (myStyles)

 * - be sure to put one style for each layer (both are separated by

 * commas).  You can also override the Opacity:

 *     myTileLayer.myOpacity=0.69

 *     myTileLayer.getOpacity=customOpacity

 *

 * Then you can overlay on google maps with something like:

 * var layer=[G_SATELLITE_MAP.getTileLayers()[0],tileCountry];

 * var custommap = new GMapType(layer, G_SATELLITE_MAP.getProjection(), "WMS");

 * var map = new GMap(document.getElementById("map"));

 *     map.addMapType(custommap);

 */

var MAGIC_NUMBER=6356752.3142;

var WGS84_SEMI_MAJOR_AXIS = 6378137.0;

var WGS84_ECCENTRICITY = 0.0818191913108718138;

var DEG2RAD=0.0174532922519943;

var PI=3.14159267;

//Default image format, used if none is specified

var FORMAT_DEFAULT="image/png";

//Google Maps Zoom level at which we switch from Mercator to Lat/Long.

var MERC_ZOOM_DEFAULT = 15;

function dd2MercMetersLng(p_lng) {

	return WGS84_SEMI_MAJOR_AXIS * (p_lng*DEG2RAD);

}

function dd2MercMetersLat(p_lat) {

	var lat_rad = p_lat * DEG2RAD;

	return WGS84_SEMI_MAJOR_AXIS * Math.log(Math.tan((lat_rad + PI / 2) / 2) * Math.pow( ((1 - WGS84_ECCENTRICITY

 * Math.sin(lat_rad)) / (1 + WGS84_ECCENTRICITY * Math.sin(lat_rad))), (WGS84_ECCENTRICITY/2)));

}

CustomGetTileUrl=function(a,b,c) {

	if (this.myMercZoomLevel == undefined) {

    	this.myMercZoomLevel = MERC_ZOOM_DEFAULT;

	}

	if (this.myFormat == undefined) {

    	this.myFormat = FORMAT_DEFAULT;

	}

	if (typeof(window['this.myStyles'])=="undefined") this.myStyles="";

	var lULP = new GPoint(a.x*256,(a.y+1)*256);

	var lLRP = new GPoint((a.x+1)*256,a.y*256);

	var lUL = G_NORMAL_MAP.getProjection().fromPixelToLatLng(lULP,b,c);

	var lLR = G_NORMAL_MAP.getProjection().fromPixelToLatLng(lLRP,b,c);

	// switch between Mercator and DD if merczoomlevel is set

	// NOTE -it is now safe to use Mercator exclusively for all zoom levels (if your WMS supports it)

	// so you can just use the two lines of code below the IF (& delete the ELSE)

	// drg & doq are topozone layers--- they don't work with epsg:54004

	

	var lBbox=lUL.x+","+lUL.y+","+lLR.x+","+lLR.y;

	var lSRS="EPSG:4326";

	var lURL=this.myBaseURL;

	lURL+="&REQUEST=GetMap";

	lURL+="&SERVICE=WMS";

	lURL+="&VERSION=1.1.1";

	lURL+="&LAYERS="+this.myLayers;

	lURL+="&STYLES="+this.myStyles;

	lURL+="&FORMAT="+this.myFormat;

	lURL+="&BGCOLOR=0xFFFFFF";

	lURL+="&TRANSPARENT=TRUE";

	lURL+="&SRS="+lSRS;

	lURL+="&BBOX="+lBbox;

	lURL+="&WIDTH=256";

	lURL+="&HEIGHT=256";

	lURL+="&reaspect=false";

	//document.write(lURL + "<br/>")

	//alert(" url is " + lURL);

	return lURL;

}

function customOpacity() { return this.myOpacity; }