85 lines
3.5 KiB
JavaScript
Executable File
85 lines
3.5 KiB
JavaScript
Executable File
// https://en.wikipedia.org/wiki/Rhumb_line
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import { convertLength, earthRadius } from "@turf/helpers";
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import { getCoord } from "@turf/invariant";
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/**
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* Calculates the distance along a rhumb line between two {@link Point|points} in degrees, radians,
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* miles, or kilometers.
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*
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* @name rhumbDistance
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* @param {Coord} from origin point
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* @param {Coord} to destination point
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* @param {Object} [options] Optional parameters
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* @param {string} [options.units="kilometers"] can be degrees, radians, miles, or kilometers
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* @returns {number} distance between the two points
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* @example
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* var from = turf.point([-75.343, 39.984]);
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* var to = turf.point([-75.534, 39.123]);
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* var options = {units: 'miles'};
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*
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* var distance = turf.rhumbDistance(from, to, options);
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*
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* //addToMap
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* var addToMap = [from, to];
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* from.properties.distance = distance;
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* to.properties.distance = distance;
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*/
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function rhumbDistance(from, to, options) {
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if (options === void 0) { options = {}; }
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var origin = getCoord(from);
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var destination = getCoord(to);
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// compensate the crossing of the 180th meridian (https://macwright.org/2016/09/26/the-180th-meridian.html)
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// solution from https://github.com/mapbox/mapbox-gl-js/issues/3250#issuecomment-294887678
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destination[0] +=
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destination[0] - origin[0] > 180
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? -360
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: origin[0] - destination[0] > 180
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? 360
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: 0;
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var distanceInMeters = calculateRhumbDistance(origin, destination);
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var distance = convertLength(distanceInMeters, "meters", options.units);
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return distance;
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}
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/**
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* Returns the distance travelling from ‘this’ point to destination point along a rhumb line.
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* Adapted from Geodesy: https://github.com/chrisveness/geodesy/blob/master/latlon-spherical.js
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*
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* @private
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* @param {Array<number>} origin point.
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* @param {Array<number>} destination point.
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* @param {number} [radius=6371e3] - (Mean) radius of earth (defaults to radius in metres).
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* @returns {number} Distance in km between this point and destination point (same units as radius).
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*
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* @example
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* var p1 = new LatLon(51.127, 1.338);
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* var p2 = new LatLon(50.964, 1.853);
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* var d = p1.distanceTo(p2); // 40.31 km
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*/
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function calculateRhumbDistance(origin, destination, radius) {
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// φ => phi
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// λ => lambda
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// ψ => psi
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// Δ => Delta
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// δ => delta
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// θ => theta
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radius = radius === undefined ? earthRadius : Number(radius);
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// see www.edwilliams.org/avform.htm#Rhumb
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var R = radius;
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var phi1 = (origin[1] * Math.PI) / 180;
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var phi2 = (destination[1] * Math.PI) / 180;
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var DeltaPhi = phi2 - phi1;
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var DeltaLambda = (Math.abs(destination[0] - origin[0]) * Math.PI) / 180;
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// if dLon over 180° take shorter rhumb line across the anti-meridian:
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if (DeltaLambda > Math.PI) {
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DeltaLambda -= 2 * Math.PI;
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}
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// on Mercator projection, longitude distances shrink by latitude; q is the 'stretch factor'
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// q becomes ill-conditioned along E-W line (0/0); use empirical tolerance to avoid it
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var DeltaPsi = Math.log(Math.tan(phi2 / 2 + Math.PI / 4) / Math.tan(phi1 / 2 + Math.PI / 4));
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var q = Math.abs(DeltaPsi) > 10e-12 ? DeltaPhi / DeltaPsi : Math.cos(phi1);
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// distance is pythagoras on 'stretched' Mercator projection
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var delta = Math.sqrt(DeltaPhi * DeltaPhi + q * q * DeltaLambda * DeltaLambda); // angular distance in radians
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var dist = delta * R;
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return dist;
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}
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export default rhumbDistance;
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