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64 lines
1.7 KiB
JavaScript
64 lines
1.7 KiB
JavaScript
var adjust_lon = require('../common/adjust_lon');
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var qsfnz = require('../common/qsfnz');
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var msfnz = require('../common/msfnz');
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var iqsfnz = require('../common/iqsfnz');
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/*
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reference:
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"Cartographic Projection Procedures for the UNIX Environment-
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A User's Manual" by Gerald I. Evenden,
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USGS Open File Report 90-284and Release 4 Interim Reports (2003)
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*/
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exports.init = function() {
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//no-op
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if (!this.sphere) {
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this.k0 = msfnz(this.e, Math.sin(this.lat_ts), Math.cos(this.lat_ts));
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}
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};
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/* Cylindrical Equal Area 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 x, y;
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/* Forward equations
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-----------------*/
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var dlon = adjust_lon(lon - this.long0);
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if (this.sphere) {
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x = this.x0 + this.a * dlon * Math.cos(this.lat_ts);
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y = this.y0 + this.a * Math.sin(lat) / Math.cos(this.lat_ts);
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}
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else {
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var qs = qsfnz(this.e, Math.sin(lat));
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x = this.x0 + this.a * this.k0 * dlon;
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y = this.y0 + this.a * qs * 0.5 / this.k0;
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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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/* Cylindrical Equal Area inverse equations--mapping x,y to lat/long
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------------------------------------------------------------*/
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exports.inverse = function(p) {
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p.x -= this.x0;
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p.y -= this.y0;
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var lon, lat;
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if (this.sphere) {
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lon = adjust_lon(this.long0 + (p.x / this.a) / Math.cos(this.lat_ts));
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lat = Math.asin((p.y / this.a) * Math.cos(this.lat_ts));
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}
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else {
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lat = iqsfnz(this.e, 2 * p.y * this.k0 / this.a);
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lon = adjust_lon(this.long0 + p.x / (this.a * this.k0));
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}
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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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exports.names = ["cea"];
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