@vizlabdev/geodesy
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Libraries of geodesy functions
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JavaScript
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
/* Vector-based ellipsoidal geodetic (latitude/longitude) functions (c) Chris Veness 2015-2021 */
/* MIT Licence */
/* www.movable-type.co.uk/scripts/latlong-vectors.html */
/* www.movable-type.co.uk/scripts/geodesy-library.html#latlon-nvector-ellipsoidal */
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
import LatLonEllipsoidal, { Cartesian, Vector3d, Dms } from './latlon-ellipsoidal.js';
/**
* Tools for working with points on (ellipsoidal models of) the earth’s surface using a vector-based
* approach using ‘n-vectors’ (rather than the more common spherical trigonometry).
*
* Based on Kenneth Gade’s ‘Non-singular Horizontal Position Representation’.
*
* Note that these formulations take x => 0°N,0°E, y => 0°N,90°E, z => 90°N (in order that n-vector
* = cartesian vector at 0°N,0°E); Gade uses x => 90°N, y => 0°N,90°E, z => 0°N,0°E.
*
* @module latlon-nvector-ellipsoidal
*/
/* LatLon_NvectorEllipsoidal - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
/**
* Latitude/longitude points on an ellipsoidal model earth augmented with methods for calculating
* delta vectors between points, and converting to n-vectors.
*
* @extends LatLonEllipsoidal
*/
class LatLon_NvectorEllipsoidal extends LatLonEllipsoidal {
/**
* Calculates delta from ‘this’ point to supplied point.
*
* The delta is given as a north-east-down NED vector. Note that this is a linear delta,
* unrelated to a geodesic on the ellipsoid.
*
* Points need not be defined on the same datum.
*
* @param {LatLon} point - Point delta is to be determined to.
* @returns {Ned} Delta from ‘this’ point to supplied point in local tangent plane of this point.
* @throws {TypeError} Invalid point.
*
* @example
* const a = new LatLon(49.66618, 3.45063, 99);
* const b = new LatLon(48.88667, 2.37472, 64);
* const delta = a.deltaTo(b); // [N:-86127,E:-78901,D:1104]
* const dist = delta.length; // 116809.178 m
* const brng = delta.bearing; // 222.493°
* const elev = delta.elevation; // -0.5416°
*/
deltaTo(point) {
if (!(point instanceof LatLonEllipsoidal)) throw new TypeError(`invalid point ‘${point}’`);
// get delta in cartesian frame
const c1 = this.toCartesian();
const c2 = point.toCartesian();
const δc = c2.minus(c1);
// get local (n-vector) coordinate frame
const n1 = this.toNvector();
const a = new Vector3d(0, 0, 1); // axis vector pointing to 90°N
const d = n1.negate(); // down (pointing opposite to n-vector)
const e = a.cross(n1).unit(); // east (pointing perpendicular to the plane)
const n = e.cross(d); // north (by right hand rule)
// rotation matrix is built from n-vector coordinate frame axes (using row vectors)
const r = [
[ n.x, n.y, n.z ],
[ e.x, e.y, e.z ],
[ d.x, d.y, d.z ],
];
// apply rotation to δc to get delta in n-vector reference frame
const δn = new Cartesian(
r[0][0]*δc.x + r[0][1]*δc.y + r[0][2]*δc.z,
r[1][0]*δc.x + r[1][1]*δc.y + r[1][2]*δc.z,
r[2][0]*δc.x + r[2][1]*δc.y + r[2][2]*δc.z,
);
return new Ned(δn.x, δn.y, δn.z);
}
/**
* Calculates destination point using supplied delta from ‘this’ point.
*
* The delta is given as a north-east-down NED vector. Note that this is a linear delta,
* unrelated to a geodesic on the ellipsoid.
*
* @param {Ned} delta - Delta from ‘this’ point to supplied point in local tangent plane of this point.
* @returns {LatLon} Destination point.
*
* @example
* const a = new LatLon(49.66618, 3.45063, 99);
* const delta = Ned.fromDistanceBearingElevation(116809.178, 222.493, -0.5416); // [N:-86127,E:-78901,D:1104]
* const b = a.destinationPoint(delta); // 48.8867°N, 002.3747°E
*/
destinationPoint(delta) {
if (!(delta instanceof Ned)) throw new TypeError('delta is not Ned object');
// convert North-East-Down delta to standard x/y/z vector in coordinate frame of n-vector
const δn = new Vector3d(delta.north, delta.east, delta.down);
// get local (n-vector) coordinate frame
const n1 = this.toNvector();
const a = new Vector3d(0, 0, 1); // axis vector pointing to 90°N
const d = n1.negate(); // down (pointing opposite to n-vector)
const e = a.cross(n1).unit(); // east (pointing perpendicular to the plane)
const n = e.cross(d); // north (by right hand rule)
// rotation matrix is built from n-vector coordinate frame axes (using column vectors)
const r = [
[ n.x, e.x, d.x ],
[ n.y, e.y, d.y ],
[ n.z, e.z, d.z ],
];
// apply rotation to δn to get delta in cartesian (ECEF) coordinate reference frame
const δc = new Cartesian(
r[0][0]*δn.x + r[0][1]*δn.y + r[0][2]*δn.z,
r[1][0]*δn.x + r[1][1]*δn.y + r[1][2]*δn.z,
r[2][0]*δn.x + r[2][1]*δn.y + r[2][2]*δn.z,
);
// apply (cartesian) delta to c1 to obtain destination point as cartesian coordinate
const c1 = this.toCartesian(); // convert this LatLon to Cartesian
const v2 = c1.plus(δc); // the plus() gives us a plain vector,..
const c2 = new Cartesian(v2.x, v2.y, v2.z); // ... need to convert it to Cartesian to get LatLon
// return destination cartesian coordinate as latitude/longitude
return c2.toLatLon();
}
/**
* Converts ‘this’ lat/lon point to n-vector (normal to the earth's surface).
*
* @returns {Nvector} N-vector representing lat/lon point.
*
* @example
* const p = new LatLon(45, 45);
* const n = p.toNvector(); // [0.5000,0.5000,0.7071]
*/
toNvector() { // note: replicated in LatLonNvectorSpherical
const φ = this.lat.toRadians();
const λ = this.lon.toRadians();
const sinφ = Math.sin(φ), cosφ = Math.cos(φ);
const sinλ = Math.sin(λ), cosλ = Math.cos(λ);
// right-handed vector: x -> 0°E,0°N; y -> 90°E,0°N, z -> 90°N
const x = cosφ * cosλ;
const y = cosφ * sinλ;
const z = sinφ;
return new NvectorEllipsoidal(x, y, z, this.h, this.datum);
}
/**
* Converts ‘this’ point from (geodetic) latitude/longitude coordinates to (geocentric) cartesian
* (x/y/z) coordinates.
*
* @returns {Cartesian} Cartesian point equivalent to lat/lon point, with x, y, z in metres from
* earth centre.
*/
toCartesian() {
const c = super.toCartesian(); // c is 'Cartesian'
// return Cartesian_Nvector to have toNvector() available as method of exported LatLon
return new Cartesian_Nvector(c.x, c.y, c.z);
}
}
/* Nvector - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
/**
* An n-vector is a position representation using a (unit) vector normal to the Earth ellipsoid.
* Unlike latitude/longitude points, n-vectors have no singularities or discontinuities.
*
* For many applications, n-vectors are more convenient to work with than other position
* representations such as latitude/longitude, earth-centred earth-fixed (ECEF) vectors, UTM
* coordinates, etc.
*
* @extends Vector3d
*/
class NvectorEllipsoidal extends Vector3d {
// note commonality with latlon-nvector-spherical
/**
* Creates a 3d n-vector normal to the Earth's surface.
*
* @param {number} x - X component of n-vector (towards 0°N, 0°E).
* @param {number} y - Y component of n-vector (towards 0°N, 90°E).
* @param {number} z - Z component of n-vector (towards 90°N).
* @param {number} [h=0] - Height above ellipsoid surface in metres.
* @param {LatLon.datums} [datum=WGS84] - Datum this n-vector is defined within.
*/
constructor(x, y, z, h=0, datum=LatLonEllipsoidal.datums.WGS84) {
const u = new Vector3d(x, y, z).unit(); // n-vectors are always normalised
super(u.x, u.y, u.z);
this.h = Number(h);
this.datum = datum;
}
/**
* Converts ‘this’ n-vector to latitude/longitude point.
*
* @returns {LatLon} Latitude/longitude point equivalent to this n-vector.
*
* @example
* const p = new Nvector(0.500000, 0.500000, 0.707107).toLatLon(); // 45.0000°N, 045.0000°E
*/
toLatLon() {
// tanφ = z / √(x²+y²), tanλ = y / x (same as spherical calculation)
const { x, y, z } = this;
const φ = Math.atan2(z, Math.sqrt(x*x + y*y));
const λ = Math.atan2(y, x);
return new LatLon_NvectorEllipsoidal(φ.toDegrees(), λ.toDegrees(), this.h, this.datum);
}
/**
* Converts ‘this’ n-vector to cartesian coordinate.
*
* qv Gade 2010 ‘A Non-singular Horizontal Position Representation’ eqn 22
*
* @returns {Cartesian} Cartesian coordinate equivalent to this n-vector.
*
* @example
* const c = new Nvector(0.500000, 0.500000, 0.707107).toCartesian(); // [3194419,3194419,4487349]
* const p = c.toLatLon(); // 45.0000°N, 045.0000°E
*/
toCartesian() {
const { b, f } = this.datum.ellipsoid;
const { x, y, z, h } = this;
const m = (1-f) * (1-f); // (1−f)² = b²/a²
const n = b / Math.sqrt(x*x/m + y*y/m + z*z);
const xʹ = n * x / m + x*h;
const yʹ = n * y / m + y*h;
const zʹ = n * z + z*h;
return new Cartesian_Nvector(xʹ, yʹ, zʹ);
}
/**
* Returns a string representation of ‘this’ (unit) n-vector. Height component is only shown if
* dpHeight is specified.
*
* @param {number} [dp=3] - Number of decimal places to display.
* @param {number} [dpHeight=null] - Number of decimal places to use for height; default is no height display.
* @returns {string} Comma-separated x, y, z, h values.
*
* @example
* new Nvector(0.5000, 0.5000, 0.7071).toString(); // [0.500,0.500,0.707]
* new Nvector(0.5000, 0.5000, 0.7071, 1).toString(6, 0); // [0.500002,0.500002,0.707103+1m]
*/
toString(dp=3, dpHeight=null) {
const { x, y, z } = this;
const h = `${this.h>=0 ? '+' : ''}${this.h.toFixed(dpHeight)}m`;
return `[${x.toFixed(dp)},${y.toFixed(dp)},${z.toFixed(dp)}${dpHeight==null ? '' : h}]`;
}
}
/* Cartesian - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
/**
* Cartesian_Nvector extends Cartesian with method to convert cartesian coordinates to n-vectors.
*
* @extends Cartesian
*/
class Cartesian_Nvector extends Cartesian {
/**
* Converts ‘this’ cartesian coordinate to an n-vector.
*
* qv Gade 2010 ‘A Non-singular Horizontal Position Representation’ eqn 23
*
* @param {LatLon.datums} [datum=WGS84] - Datum to use for conversion.
* @returns {Nvector} N-vector equivalent to this cartesian coordinate.
*
* @example
* const c = new Cartesian(3980581, 97, 4966825);
* const n = c.toNvector(); // { x: 0.6228, y: 0.0000, z: 0.7824, h: 0.0000 }
*/
toNvector(datum=LatLonEllipsoidal.datums.WGS84) {
const { a, f } = datum.ellipsoid;
const { x, y, z } = this;
const e2 = 2*f - f*f; // e² = 1st eccentricity squared ≡ (a²-b²)/a²
const e4 = e2*e2; // e⁴
const p = (x*x + y*y) / (a*a);
const q = z*z * (1-e2) / (a*a);
const r = (p + q - e4) / 6;
const s = (e4*p*q) / (4*r*r*r);
const t = Math.cbrt(1 + s + Math.sqrt(2*s+s*s));
const u = r * (1 + t + 1/t);
const v = Math.sqrt(u*u + e4*q);
const w = e2 * (u + v - q) / (2*v);
const k = Math.sqrt(u + v + w*w) - w;
const d = k * Math.sqrt(x*x + y*y) / (k + e2);
const tmp = 1 / Math.sqrt(d*d + z*z);
const xʹ = tmp * k/(k+e2) * x;
const yʹ = tmp * k/(k+e2) * y;
const zʹ = tmp * z;
const h = (k + e2 - 1)/k * Math.sqrt(d*d + z*z);
const n = new NvectorEllipsoidal(xʹ, yʹ, zʹ, h, datum);
return n;
}
}
/* Ned - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
/**
* North-east-down (NED), also known as local tangent plane (LTP), is a vector in the local
* coordinate frame of a body.
*/
class Ned {
/**
* Creates North-East-Down vector.
*
* @param {number} north - North component in metres.
* @param {number} east - East component in metres.
* @param {number} down - Down component (normal to the surface of the ellipsoid) in metres.
*
* @example
* import { Ned } from '/js/geodesy/latlon-nvector-ellipsoidal.js';
* const delta = new Ned(110569, 111297, 1936); // [N:110569,E:111297,D:1936]
*/
constructor(north, east, down) {
this.north = north;
this.east = east;
this.down = down;
}
/**
* Length of NED vector.
*
* @returns {number} Length of NED vector in metres.
*/
get length() {
const { north, east, down } = this;
return Math.sqrt(north*north + east*east + down*down);
}
/**
* Bearing of NED vector.
*
* @returns {number} Bearing of NED vector in degrees from north.
*/
get bearing() {
const θ = Math.atan2(this.east, this.north);
return Dms.wrap360(θ.toDegrees()); // normalise to range 0..360°
}
/**
* Elevation of NED vector.
*
* @returns {number} Elevation of NED vector in degrees from horizontal (ie tangent to ellipsoid surface).
*/
get elevation() {
const α = Math.asin(this.down/this.length);
return -α.toDegrees();
}
/**
* Creates North-East-Down vector from distance, bearing, & elevation (in local coordinate system).
*
* @param {number} dist - Length of NED vector in metres.
* @param {number} brng - Bearing (in degrees from north) of NED vector .
* @param {number} elev - Elevation (in degrees from local coordinate frame horizontal) of NED vector.
* @returns {Ned} North-East-Down vector equivalent to distance, bearing, elevation.
*
* @example
* const delta = Ned.fromDistanceBearingElevation(116809.178, 222.493, -0.5416); // [N:-86127,E:-78901,D:1104]
*/
static fromDistanceBearingElevation(dist, brng, elev) {
const θ = Number(brng).toRadians();
const α = Number(elev).toRadians();
dist = Number(dist);
const sinθ = Math.sin(θ), cosθ = Math.cos(θ);
const sinα = Math.sin(α), cosα = Math.cos(α);
const n = cosθ * dist*cosα;
const e = sinθ * dist*cosα;
const d = -sinα * dist;
return new Ned(n, e, d);
}
/**
* Returns a string representation of ‘this’ NED vector.
*
* @param {number} [dp=0] - Number of decimal places to display.
* @returns {string} Comma-separated (labelled) n, e, d values.
*/
toString(dp=0) {
return `[N:${this.north.toFixed(dp)},E:${this.east.toFixed(dp)},D:${this.down.toFixed(dp)}]`;
}
}
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
export { LatLon_NvectorEllipsoidal as default, NvectorEllipsoidal as Nvector, Cartesian_Nvector as Cartesian, Ned, Dms };