175 lines
6.7 KiB
JavaScript
175 lines
6.7 KiB
JavaScript
'use strict';
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Object.defineProperty(exports, '__esModule', { value: true });
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var base = require('./base.cjs');
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var globe = require('./globe.cjs');
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var sidereal = require('./sidereal.cjs');
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var sexagesimal = require('./sexagesimal.cjs');
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/**
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* @copyright 2013 Sonia Keys
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* @copyright 2016 commenthol
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* @license MIT
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* @module parallax
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*/
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const horPar = (8.794 / 3600) * Math.PI / 180; // 8".794 arcseconds in radians
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/**
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* Horizontal returns equatorial horizontal parallax of a body.
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*
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* @param {number} Δ - distance in AU.
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* @return {number} parallax in radians.
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*/
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function horizontal (Δ) {
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// (40.1) p. 279
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return Math.asin(Math.sin(horPar) / Δ)
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// return horPar / Δ // with sufficient accuracy
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}
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/**
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* Topocentric returns topocentric positions including parallax.
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*
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* Arguments α, δ are geocentric right ascension and declination in radians.
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* Δ is distance to the observed object in AU. ρsφ, ρcφ are parallax
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* constants (see package globe.) lon is geographic longitude of the observer,
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* jde is time of observation.
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*
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* @param {Coord} c - geocentric right ascension and declination in radians
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* @param {number} ρsφ - parallax constants (see package globe.)
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* @param {number} ρcφ - parallax constants (see package globe.)
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* @param {number} lon - geographic longitude of the observer (measured positively westwards!)
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* @param {number} jde - time of observation
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* @return {Coord} observed topocentric ra and dec in radians.
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*/
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function topocentric (c, ρsφ, ρcφ, lon, jde) {
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const [α, δ, Δ] = [c.ra, c.dec, c.range];
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const π = horizontal(Δ);
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const θ0 = new sexagesimal["default"].Time(sidereal["default"].apparent(jde)).rad();
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const H = base["default"].pmod(θ0 - lon - α, 2 * Math.PI);
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const sπ = Math.sin(π);
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const [sH, cH] = base["default"].sincos(H);
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const [sδ, cδ] = base["default"].sincos(δ);
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const Δα = Math.atan2(-ρcφ * sπ * sH, cδ - ρcφ * sπ * cH); // (40.2) p. 279
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const α_ = α + Δα;
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const δ_ = Math.atan2((sδ - ρsφ * sπ) * Math.cos(Δα), cδ - ρcφ * sπ * cH); // (40.3) p. 279
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return new base.Coord(α_, δ_)
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}
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/**
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* Topocentric2 returns topocentric corrections including parallax.
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*
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* This function implements the "non-rigorous" method descripted in the text.
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*
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* Note that results are corrections, not corrected coordinates.
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*
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* @param {Coord} c - geocentric right ascension and declination in radians
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* @param {number} ρsφ - parallax constants (see package globe.)
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* @param {number} ρcφ - parallax constants (see package globe.)
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* @param {number} lon - geographic longitude of the observer (measured positively westwards!)
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* @param {number} jde - time of observation
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* @return {Coord} observed topocentric ra and dec in radians.
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*/
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function topocentric2 (c, ρsφ, ρcφ, lon, jde) {
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const [α, δ, Δ] = [c.ra, c.dec, c.range];
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const π = horizontal(Δ);
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const θ0 = new sexagesimal["default"].Time(sidereal["default"].apparent(jde)).rad();
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const H = base["default"].pmod(θ0 - lon - α, 2 * Math.PI);
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const [sH, cH] = base["default"].sincos(H);
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const [sδ, cδ] = base["default"].sincos(δ);
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const Δα = -π * ρcφ * sH / cδ; // (40.4) p. 280
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const Δδ = -π * (ρsφ * cδ - ρcφ * cH * sδ); // (40.5) p. 280
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return new base["default"].Coord(Δα, Δδ)
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}
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/**
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* Topocentric3 returns topocentric hour angle and declination including parallax.
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*
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* This function implements the "alternative" method described in the text.
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* The method should be similarly rigorous to that of Topocentric() and results
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* should be virtually consistent.
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*
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* @param {Coord} c - geocentric right ascension and declination in radians
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* @param {number} ρsφ - parallax constants (see package globe.)
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* @param {number} ρcφ - parallax constants (see package globe.)
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* @param {number} lon - geographic longitude of the observer (measured positively westwards!)
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* @param {number} jde - time of observation
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* @return {Array}
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* {number} H_ - topocentric hour angle
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* {number} δ_ - topocentric declination
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*/
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function topocentric3 (c, ρsφ, ρcφ, lon, jde) {
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const [α, δ, Δ] = [c.ra, c.dec, c.range];
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const π = horizontal(Δ);
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const θ0 = new sexagesimal["default"].Time(sidereal["default"].apparent(jde)).rad();
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const H = base["default"].pmod(θ0 - lon - α, 2 * Math.PI);
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const sπ = Math.sin(π);
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const [sH, cH] = base["default"].sincos(H);
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const [sδ, cδ] = base["default"].sincos(δ);
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const A = cδ * sH;
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const B = cδ * cH - ρcφ * sπ;
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const C = sδ - ρsφ * sπ;
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const q = Math.sqrt(A * A + B * B + C * C);
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const H_ = Math.atan2(A, B);
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const δ_ = Math.asin(C / q);
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return [H_, δ_]
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}
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/**
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* TopocentricEcliptical returns topocentric ecliptical coordinates including parallax.
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*
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* Arguments `c` are geocentric ecliptical longitude and latitude of a body,
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* s is its geocentric semidiameter. φ, h are the observer's latitude and
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* and height above the ellipsoid in meters. ε is the obliquity of the
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* ecliptic, θ is local sidereal time, π is equatorial horizontal parallax
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* of the body (see Horizonal()).
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*
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* All angular parameters and results are in radians.
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*
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* @param {Coord} c - geocentric right ascension and declination in radians
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* @param {number} s - geocentric semidiameter of `c`
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* @param {number} φ - observer's latitude
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* @param {number} h - observer's height above the ellipsoid in meters
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* @param {number} ε - is the obliquity of the ecliptic
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* @param {number} θ - local sidereal time
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* @param {number} π - equatorial horizontal parallax of the body
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* @return {Array}
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* {number} λ_ - observed topocentric longitude
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* {number} β_ - observed topocentric latitude
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* {number} s_ - observed topocentric semidiameter
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*/
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function topocentricEcliptical (c, s, φ, h, ε, θ, π) {
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const [λ, β] = [c.lon, c.lat];
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const [S, C] = globe["default"].Earth76.parallaxConstants(φ, h);
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const [sλ, cλ] = base["default"].sincos(λ);
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const [sβ, cβ] = base["default"].sincos(β);
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const [sε, cε] = base["default"].sincos(ε);
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const [sθ, cθ] = base["default"].sincos(θ);
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const sπ = Math.sin(π);
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const N = cλ * cβ - C * sπ * cθ;
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let λ_ = Math.atan2(sλ * cβ - sπ * (S * sε + C * cε * sθ), N);
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if (λ_ < 0) {
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λ_ += 2 * Math.PI;
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}
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const cλ_ = Math.cos(λ_);
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const β_ = Math.atan(cλ_ * (sβ - sπ * (S * cε - C * sε * sθ)) / N);
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const s_ = Math.asin(cλ_ * Math.cos(β_) * Math.sin(s) / N);
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return [λ_, β_, s_]
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}
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var parallax = {
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horizontal,
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topocentric,
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topocentric2,
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topocentric3,
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topocentricEcliptical
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};
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exports["default"] = parallax;
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exports.horizontal = horizontal;
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exports.topocentric = topocentric;
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exports.topocentric2 = topocentric2;
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exports.topocentric3 = topocentric3;
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exports.topocentricEcliptical = topocentricEcliptical;
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