/*******************************************************************************
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NAME MERCATOR
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PURPOSE: Transforms input longitude and latitude to Easting and
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Northing for the Mercator projection. The
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longitude and latitude must be in radians. The Easting
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and Northing values will be returned in meters.
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PROGRAMMER DATE
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---------- ----
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D. Steinwand, EROS Nov, 1991
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T. Mittan Mar, 1993
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ALGORITHM REFERENCES
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1. Snyder, John P., "Map Projections--A Working Manual", U.S. Geological
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Survey Professional Paper 1395 (Supersedes USGS Bulletin 1532), United
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State Government Printing Office, Washington D.C., 1987.
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2. Snyder, John P. and Voxland, Philip M., "An Album of Map Projections",
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U.S. Geological Survey Professional Paper 1453 , United State Government
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Printing Office, Washington D.C., 1989.
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*******************************************************************************/
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//static double r_major = a; /* major axis */
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//static double r_minor = b; /* minor axis */
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//static double lon_center = long0; /* Center longitude (projection center) */
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//static double lat_origin = lat0; /* center latitude */
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//static double e,es; /* eccentricity constants */
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//static double m1; /* small value m */
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//static double false_northing = y0; /* y offset in meters */
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//static double false_easting = x0; /* x offset in meters */
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//scale_fact = k0
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Proj4js.Proj.merc = {
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init : function() {
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//?this.temp = this.r_minor / this.r_major;
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//this.temp = this.b / this.a;
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//this.es = 1.0 - Math.sqrt(this.temp);
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//this.e = Math.sqrt( this.es );
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//?this.m1 = Math.cos(this.lat_origin) / (Math.sqrt( 1.0 - this.es * Math.sin(this.lat_origin) * Math.sin(this.lat_origin)));
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//this.m1 = Math.cos(0.0) / (Math.sqrt( 1.0 - this.es * Math.sin(0.0) * Math.sin(0.0)));
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if (this.lat_ts) {
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if (this.sphere) {
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this.k0 = Math.cos(this.lat_ts);
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} else {
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this.k0 = Proj4js.common.msfnz(this.es, Math.sin(this.lat_ts), Math.cos(this.lat_ts));
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}
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}
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},
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/* Mercator forward equations--mapping lat,long to x,y
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--------------------------------------------------*/
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forward : function(p) {
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//alert("ll2m coords : "+coords);
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var lon = p.x;
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var lat = p.y;
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// convert to radians
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if ( lat*Proj4js.common.R2D > 90.0 &&
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lat*Proj4js.common.R2D < -90.0 &&
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lon*Proj4js.common.R2D > 180.0 &&
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lon*Proj4js.common.R2D < -180.0) {
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Proj4js.reportError("merc:forward: llInputOutOfRange: "+ lon +" : " + lat);
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return null;
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}
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var x,y;
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if(Math.abs( Math.abs(lat) - Proj4js.common.HALF_PI) <= Proj4js.common.EPSLN) {
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Proj4js.reportError("merc:forward: ll2mAtPoles");
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return null;
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} else {
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if (this.sphere) {
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x = this.x0 + this.a * this.k0 * Proj4js.common.adjust_lon(lon - this.long0);
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y = this.y0 + this.a * this.k0 * Math.log(Math.tan(Proj4js.common.FORTPI + 0.5*lat));
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} else {
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var sinphi = Math.sin(lat);
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var ts = Proj4js.common.tsfnz(this.e,lat,sinphi);
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x = this.x0 + this.a * this.k0 * Proj4js.common.adjust_lon(lon - this.long0);
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y = this.y0 - this.a * this.k0 * Math.log(ts);
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}
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p.x = x;
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p.y = y;
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return p;
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}
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},
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/* Mercator inverse equations--mapping x,y to lat/long
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--------------------------------------------------*/
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inverse : function(p) {
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var x = p.x - this.x0;
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var y = p.y - this.y0;
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var lon,lat;
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if (this.sphere) {
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lat = Proj4js.common.HALF_PI - 2.0 * Math.atan(Math.exp(-y / this.a * this.k0));
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} else {
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var ts = Math.exp(-y / (this.a * this.k0));
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lat = Proj4js.common.phi2z(this.e,ts);
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if(lat == -9999) {
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Proj4js.reportError("merc:inverse: lat = -9999");
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return null;
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}
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}
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lon = Proj4js.common.adjust_lon(this.long0+ x / (this.a * this.k0));
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p.x = lon;
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p.y = lat;
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return p;
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}
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};
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