/*
* 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
    if (this.myLayers != "drg" && this.myLayers != "doq") {
        var lBbox = dd2MercMetersLng(lUL.x) + "," + dd2MercMetersLat(lUL.y) + "," + dd2MercMetersLng(lLR.x) + "," + dd2MercMetersLat(lLR.y);
        //Change for GeoServer - 41001 is mercator and installed by default.
        var lSRS = "EPSG:54004";
    } else {
        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; }