105 lines
2.7 KiB
JavaScript
105 lines
2.7 KiB
JavaScript
import adjust_lon from '../common/adjust_lon';
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import asinz from '../common/asinz';
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import {EPSLN} from '../constants/values';
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/*
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reference:
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Wolfram Mathworld "Gnomonic Projection"
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http://mathworld.wolfram.com/GnomonicProjection.html
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Accessed: 12th November 2009
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*/
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export function init() {
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/* Place parameters in static storage for common use
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-------------------------------------------------*/
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this.sin_p14 = Math.sin(this.lat0);
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this.cos_p14 = Math.cos(this.lat0);
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// Approximation for projecting points to the horizon (infinity)
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this.infinity_dist = 1000 * this.a;
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this.rc = 1;
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}
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/* Gnomonic forward equations--mapping lat,long to x,y
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---------------------------------------------------*/
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export function forward(p) {
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var sinphi, cosphi; /* sin and cos value */
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var dlon; /* delta longitude value */
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var coslon; /* cos of longitude */
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var ksp; /* scale factor */
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var g;
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var x, y;
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var lon = p.x;
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var lat = p.y;
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/* Forward equations
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-----------------*/
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dlon = adjust_lon(lon - this.long0);
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sinphi = Math.sin(lat);
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cosphi = Math.cos(lat);
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coslon = Math.cos(dlon);
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g = this.sin_p14 * sinphi + this.cos_p14 * cosphi * coslon;
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ksp = 1;
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if ((g > 0) || (Math.abs(g) <= EPSLN)) {
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x = this.x0 + this.a * ksp * cosphi * Math.sin(dlon) / g;
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y = this.y0 + this.a * ksp * (this.cos_p14 * sinphi - this.sin_p14 * cosphi * coslon) / g;
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}
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else {
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// Point is in the opposing hemisphere and is unprojectable
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// We still need to return a reasonable point, so we project
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// to infinity, on a bearing
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// equivalent to the northern hemisphere equivalent
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// This is a reasonable approximation for short shapes and lines that
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// straddle the horizon.
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x = this.x0 + this.infinity_dist * cosphi * Math.sin(dlon);
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y = this.y0 + this.infinity_dist * (this.cos_p14 * sinphi - this.sin_p14 * cosphi * coslon);
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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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export function inverse(p) {
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var rh; /* Rho */
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var sinc, cosc;
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var c;
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var lon, lat;
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/* Inverse equations
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-----------------*/
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p.x = (p.x - this.x0) / this.a;
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p.y = (p.y - this.y0) / this.a;
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p.x /= this.k0;
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p.y /= this.k0;
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if ((rh = Math.sqrt(p.x * p.x + p.y * p.y))) {
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c = Math.atan2(rh, this.rc);
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sinc = Math.sin(c);
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cosc = Math.cos(c);
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lat = asinz(cosc * this.sin_p14 + (p.y * sinc * this.cos_p14) / rh);
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lon = Math.atan2(p.x * sinc, rh * this.cos_p14 * cosc - p.y * this.sin_p14 * sinc);
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lon = adjust_lon(this.long0 + lon);
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}
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else {
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lat = this.phic0;
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lon = 0;
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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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export var names = ["gnom"];
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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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