Proj4js.Proj.gstmerc = {
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init : function() {
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// array of: a, b, lon0, lat0, k0, x0, y0
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var temp= this.b / this.a;
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this.e= Math.sqrt(1.0 - temp*temp);
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this.lc= this.long0;
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this.rs= Math.sqrt(1.0+this.e*this.e*Math.pow(Math.cos(this.lat0),4.0)/(1.0-this.e*this.e));
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var sinz= Math.sin(this.lat0);
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var pc= Math.asin(sinz/this.rs);
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var sinzpc= Math.sin(pc);
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this.cp= Proj4js.common.latiso(0.0,pc,sinzpc)-this.rs*Proj4js.common.latiso(this.e,this.lat0,sinz);
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this.n2= this.k0*this.a*Math.sqrt(1.0-this.e*this.e)/(1.0-this.e*this.e*sinz*sinz);
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this.xs= this.x0;
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this.ys= this.y0-this.n2*pc;
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if (!this.title) this.title = "Gauss Schreiber transverse mercator";
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},
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// forward equations--mapping lat,long to x,y
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// -----------------------------------------------------------------
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forward : function(p) {
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var lon= p.x;
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var lat= p.y;
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var L= this.rs*(lon-this.lc);
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var Ls= this.cp+(this.rs*Proj4js.common.latiso(this.e,lat,Math.sin(lat)));
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var lat1= Math.asin(Math.sin(L)/Proj4js.common.cosh(Ls));
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var Ls1= Proj4js.common.latiso(0.0,lat1,Math.sin(lat1));
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p.x= this.xs+(this.n2*Ls1);
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p.y= this.ys+(this.n2*Math.atan(Proj4js.common.sinh(Ls)/Math.cos(L)));
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return p;
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},
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// 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;
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var y= p.y;
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var L= Math.atan(Proj4js.common.sinh((x-this.xs)/this.n2)/Math.cos((y-this.ys)/this.n2));
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var lat1= Math.asin(Math.sin((y-this.ys)/this.n2)/Proj4js.common.cosh((x-this.xs)/this.n2));
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var LC= Proj4js.common.latiso(0.0,lat1,Math.sin(lat1));
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p.x= this.lc+L/this.rs;
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p.y= Proj4js.common.invlatiso(this.e,(LC-this.cp)/this.rs);
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return p;
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}
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};
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