var latiso = require('../common/latiso');
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var sinh = require('../common/sinh');
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var cosh = require('../common/cosh');
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var invlatiso = require('../common/invlatiso');
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exports.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 - temp * temp);
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this.lc = this.long0;
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this.rs = Math.sqrt(1 + this.e * this.e * Math.pow(Math.cos(this.lat0), 4) / (1 - 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 = latiso(0, pc, sinzpc) - this.rs * latiso(this.e, this.lat0, sinz);
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this.n2 = this.k0 * this.a * Math.sqrt(1 - this.e * this.e) / (1 - 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) {
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this.title = "Gauss Schreiber transverse mercator";
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}
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};
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// forward equations--mapping lat,long to x,y
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// -----------------------------------------------------------------
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exports.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 * latiso(this.e, lat, Math.sin(lat)));
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var lat1 = Math.asin(Math.sin(L) / cosh(Ls));
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var Ls1 = latiso(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(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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exports.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(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) / cosh((x - this.xs) / this.n2));
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var LC = latiso(0, lat1, Math.sin(lat1));
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p.x = this.lc + L / this.rs;
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p.y = invlatiso(this.e, (LC - this.cp) / this.rs);
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return p;
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};
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exports.names = ["gstmerg"];
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