84 lines
2.2 KiB
JavaScript
84 lines
2.2 KiB
JavaScript
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import adjust_lon from '../common/adjust_lon';
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export function init() {}
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import {EPSLN} from '../constants/values';
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/* Mollweide forward equations--mapping lat,long to x,y
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----------------------------------------------------*/
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export function forward(p) {
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/* Forward equations
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-----------------*/
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var lon = p.x;
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var lat = p.y;
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var delta_lon = adjust_lon(lon - this.long0);
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var theta = lat;
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var con = Math.PI * Math.sin(lat);
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/* Iterate using the Newton-Raphson method to find theta
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-----------------------------------------------------*/
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while (true) {
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var delta_theta = -(theta + Math.sin(theta) - con) / (1 + Math.cos(theta));
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theta += delta_theta;
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if (Math.abs(delta_theta) < EPSLN) {
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break;
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}
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}
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theta /= 2;
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/* If the latitude is 90 deg, force the x coordinate to be "0 + false easting"
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this is done here because of precision problems with "cos(theta)"
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--------------------------------------------------------------------------*/
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if (Math.PI / 2 - Math.abs(lat) < EPSLN) {
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delta_lon = 0;
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}
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var x = 0.900316316158 * this.a * delta_lon * Math.cos(theta) + this.x0;
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var y = 1.4142135623731 * this.a * Math.sin(theta) + this.y0;
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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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export function inverse(p) {
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var theta;
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var arg;
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/* Inverse equations
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-----------------*/
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p.x -= this.x0;
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p.y -= this.y0;
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arg = p.y / (1.4142135623731 * this.a);
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/* Because of division by zero problems, 'arg' can not be 1. Therefore
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a number very close to one is used instead.
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-------------------------------------------------------------------*/
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if (Math.abs(arg) > 0.999999999999) {
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arg = 0.999999999999;
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}
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theta = Math.asin(arg);
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var lon = adjust_lon(this.long0 + (p.x / (0.900316316158 * this.a * Math.cos(theta))));
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if (lon < (-Math.PI)) {
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lon = -Math.PI;
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}
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if (lon > Math.PI) {
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lon = Math.PI;
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}
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arg = (2 * theta + Math.sin(2 * theta)) / Math.PI;
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if (Math.abs(arg) > 1) {
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arg = 1;
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}
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var lat = Math.asin(arg);
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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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export var names = ["Mollweide", "moll"];
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export default {
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init: init,
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forward: forward,
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inverse: inverse,
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names: names
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};
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