mirror of https://github.com/espruino/BangleApps
129 lines
4.8 KiB
JavaScript
129 lines
4.8 KiB
JavaScript
/**
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*
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* A module of Geo functions for use with gps fixes
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*
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* let geo = require("geotools");
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* let os = geo.gpsToOSGrid(fix);
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* let ref = geo.gpsToOSMapRef(fix);
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*
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*/
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Number.prototype.toRad = function() { return this*Math.PI/180; };
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/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
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/* Ordnance Survey Grid Reference functions (c) Chris Veness 2005-2014 */
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/* - www.movable-type.co.uk/scripts/gridref.js */
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/* - www.movable-type.co.uk/scripts/latlon-gridref.html */
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/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
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function OsGridRef(easting, northing) {
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this.easting = 0|easting;
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this.northing = 0|northing;
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}
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OsGridRef.latLongToOsGrid = function(point) {
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var lat = point.lat.toRad();
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var lon = point.lon.toRad();
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var a = 6377563.396, b = 6356256.909; // Airy 1830 major & minor semi-axes
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var F0 = 0.9996012717; // NatGrid scale factor on central meridian
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var lat0 = (49).toRad(), lon0 = (-2).toRad(); // NatGrid true origin is 49�N,2�W
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var N0 = -100000, E0 = 400000; // northing & easting of true origin, metres
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var e2 = 1 - (b*b)/(a*a); // eccentricity squared
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var n = (a-b)/(a+b), n2 = n*n, n3 = n*n*n;
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var cosLat = Math.cos(lat), sinLat = Math.sin(lat);
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var nu = a*F0/Math.sqrt(1-e2*sinLat*sinLat); // transverse radius of curvature
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var rho = a*F0*(1-e2)/Math.pow(1-e2*sinLat*sinLat, 1.5); // meridional radius of curvature
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var eta2 = nu/rho-1;
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var Ma = (1 + n + (5/4)*n2 + (5/4)*n3) * (lat-lat0);
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var Mb = (3*n + 3*n*n + (21/8)*n3) * Math.sin(lat-lat0) * Math.cos(lat+lat0);
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var Mc = ((15/8)*n2 + (15/8)*n3) * Math.sin(2*(lat-lat0)) * Math.cos(2*(lat+lat0));
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var Md = (35/24)*n3 * Math.sin(3*(lat-lat0)) * Math.cos(3*(lat+lat0));
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var M = b * F0 * (Ma - Mb + Mc - Md); // meridional arc
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var cos3lat = cosLat*cosLat*cosLat;
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var cos5lat = cos3lat*cosLat*cosLat;
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var tan2lat = Math.tan(lat)*Math.tan(lat);
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var tan4lat = tan2lat*tan2lat;
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var I = M + N0;
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var II = (nu/2)*sinLat*cosLat;
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var III = (nu/24)*sinLat*cos3lat*(5-tan2lat+9*eta2);
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var IIIA = (nu/720)*sinLat*cos5lat*(61-58*tan2lat+tan4lat);
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var IV = nu*cosLat;
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var V = (nu/6)*cos3lat*(nu/rho-tan2lat);
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var VI = (nu/120) * cos5lat * (5 - 18*tan2lat + tan4lat + 14*eta2 - 58*tan2lat*eta2);
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var dLon = lon-lon0;
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var dLon2 = dLon*dLon, dLon3 = dLon2*dLon, dLon4 = dLon3*dLon, dLon5 = dLon4*dLon, dLon6 = dLon5*dLon;
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var N = I + II*dLon2 + III*dLon4 + IIIA*dLon6;
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var E = E0 + IV*dLon + V*dLon3 + VI*dLon5;
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return new OsGridRef(E, N);
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};
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/*
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* converts northing, easting to standard OS grid reference.
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*
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* [digits=10] - precision (10 digits = metres)
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* to_map_ref(8, 651409, 313177); => 'TG 5140 1317'
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* to_map_ref(0, 651409, 313177); => '651409,313177'
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*
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*/
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function to_map_ref(digits, easting, northing) {
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if (![ 0,2,4,6,8,10,12,14,16 ].includes(Number(digits))) throw new RangeError(`invalid precision '${digits}'`);
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let e = easting;
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let n = northing;
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// use digits = 0 to return numeric format (in metres) - note northing may be >= 1e7
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if (digits == 0) {
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const format = { useGrouping: false, minimumIntegerDigits: 6, maximumFractionDigits: 3 };
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const ePad = e.toLocaleString('en', format);
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const nPad = n.toLocaleString('en', format);
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return `${ePad},${nPad}`;
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}
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// get the 100km-grid indices
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const e100km = Math.floor(e / 100000), n100km = Math.floor(n / 100000);
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// translate those into numeric equivalents of the grid letters
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let l1 = (19 - n100km) - (19 - n100km) % 5 + Math.floor((e100km + 10) / 5);
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let l2 = (19 - n100km) * 5 % 25 + e100km % 5;
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// compensate for skipped 'I' and build grid letter-pairs
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if (l1 > 7) l1++;
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if (l2 > 7) l2++;
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const letterPair = String.fromCharCode(l1 + 'A'.charCodeAt(0), l2 + 'A'.charCodeAt(0));
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// strip 100km-grid indices from easting & northing, and reduce precision
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e = Math.floor((e % 100000) / Math.pow(10, 5 - digits / 2));
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n = Math.floor((n % 100000) / Math.pow(10, 5 - digits / 2));
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// pad eastings & northings with leading zeros
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e = e.toString().padStart(digits/2, '0');
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n = n.toString().padStart(digits/2, '0');
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return `${letterPair} ${e} ${n}`;
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}
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/**
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*
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* Module exports section, example code below
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*
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* let geo = require("geotools");
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* let os = geo.gpsToOSGrid(fix);
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* let ref = geo.gpsToOSMapRef(fix);
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*/
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// get easting and northings
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exports.gpsToOSGrid = function(gps_fix) {
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return OsGridRef.latLongToOsGrid(gps_fix);
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}
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// string with an OS Map grid reference
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exports.gpsToOSMapRef = function(gps_fix) {
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let os = OsGridRef.latLongToOsGrid(gps_fix);
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return to_map_ref(6, os.easting, os.northing);
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}
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