EllipsoidGeodesic.js

define([
        './Cartesian3',
        './Cartographic',
        './Check',
        './defaultValue',
        './defined',
        './defineProperties',
        './Ellipsoid',
        './Math'
    ], function(
        Cartesian3,
        Cartographic,
        Check,
        defaultValue,
        defined,
        defineProperties,
        Ellipsoid,
        CesiumMath) {
    'use strict';

    function setConstants(ellipsoidGeodesic) {
        var uSquared = ellipsoidGeodesic._uSquared;
        var a = ellipsoidGeodesic._ellipsoid.maximumRadius;
        var b = ellipsoidGeodesic._ellipsoid.minimumRadius;
        var f = (a - b) / a;

        var cosineHeading = Math.cos(ellipsoidGeodesic._startHeading);
        var sineHeading = Math.sin(ellipsoidGeodesic._startHeading);

        var tanU = (1 - f) * Math.tan(ellipsoidGeodesic._start.latitude);

        var cosineU = 1.0 / Math.sqrt(1.0 + tanU * tanU);
        var sineU = cosineU * tanU;

        var sigma = Math.atan2(tanU, cosineHeading);

        var sineAlpha = cosineU * sineHeading;
        var sineSquaredAlpha = sineAlpha * sineAlpha;

        var cosineSquaredAlpha = 1.0 - sineSquaredAlpha;
        var cosineAlpha = Math.sqrt(cosineSquaredAlpha);

        var u2Over4 = uSquared / 4.0;
        var u4Over16 = u2Over4 * u2Over4;
        var u6Over64 = u4Over16 * u2Over4;
        var u8Over256 = u4Over16 * u4Over16;

        var a0 = (1.0 + u2Over4 - 3.0 * u4Over16 / 4.0 + 5.0 * u6Over64 / 4.0 - 175.0 * u8Over256 / 64.0);
        var a1 = (1.0 - u2Over4 + 15.0 * u4Over16 / 8.0 - 35.0 * u6Over64 / 8.0);
        var a2 = (1.0 - 3.0 * u2Over4 + 35.0 * u4Over16 / 4.0);
        var a3 = (1.0 - 5.0 * u2Over4);

        var distanceRatio = a0 * sigma - a1 * Math.sin(2.0 * sigma) * u2Over4 / 2.0 - a2 * Math.sin(4.0 * sigma) * u4Over16 / 16.0 -
                            a3 * Math.sin(6.0 * sigma) * u6Over64 / 48.0 - Math.sin(8.0 * sigma) * 5.0 * u8Over256 / 512;

        var constants = ellipsoidGeodesic._constants;

        constants.a = a;
        constants.b = b;
        constants.f = f;
        constants.cosineHeading = cosineHeading;
        constants.sineHeading = sineHeading;
        constants.tanU = tanU;
        constants.cosineU = cosineU;
        constants.sineU = sineU;
        constants.sigma = sigma;
        constants.sineAlpha = sineAlpha;
        constants.sineSquaredAlpha = sineSquaredAlpha;
        constants.cosineSquaredAlpha = cosineSquaredAlpha;
        constants.cosineAlpha = cosineAlpha;
        constants.u2Over4 = u2Over4;
        constants.u4Over16 = u4Over16;
        constants.u6Over64 = u6Over64;
        constants.u8Over256 = u8Over256;
        constants.a0 = a0;
        constants.a1 = a1;
        constants.a2 = a2;
        constants.a3 = a3;
        constants.distanceRatio = distanceRatio;
    }

    function computeC(f, cosineSquaredAlpha) {
        return f * cosineSquaredAlpha * (4.0 + f * (4.0 - 3.0 * cosineSquaredAlpha)) / 16.0;
    }

    function computeDeltaLambda(f, sineAlpha, cosineSquaredAlpha, sigma, sineSigma, cosineSigma, cosineTwiceSigmaMidpoint) {
        var C = computeC(f, cosineSquaredAlpha);

        return (1.0 - C) * f * sineAlpha * (sigma + C * sineSigma * (cosineTwiceSigmaMidpoint +
                C * cosineSigma * (2.0 * cosineTwiceSigmaMidpoint * cosineTwiceSigmaMidpoint - 1.0)));
    }

    function vincentyInverseFormula(ellipsoidGeodesic, major, minor, firstLongitude, firstLatitude, secondLongitude, secondLatitude) {
        var eff = (major - minor) / major;
        var l = secondLongitude - firstLongitude;

        var u1 = Math.atan((1 - eff) * Math.tan(firstLatitude));
        var u2 = Math.atan((1 - eff) * Math.tan(secondLatitude));

        var cosineU1 = Math.cos(u1);
        var sineU1 = Math.sin(u1);
        var cosineU2 = Math.cos(u2);
        var sineU2 = Math.sin(u2);

        var cc = cosineU1 * cosineU2;
        var cs = cosineU1 * sineU2;
        var ss = sineU1 * sineU2;
        var sc = sineU1 * cosineU2;

        var lambda = l;
        var lambdaDot = CesiumMath.TWO_PI;

        var cosineLambda = Math.cos(lambda);
        var sineLambda = Math.sin(lambda);

        var sigma;
        var cosineSigma;
        var sineSigma;
        var cosineSquaredAlpha;
        var cosineTwiceSigmaMidpoint;

        do {
            cosineLambda = Math.cos(lambda);
            sineLambda = Math.sin(lambda);

            var temp = cs - sc * cosineLambda;
            sineSigma = Math.sqrt(cosineU2 * cosineU2 * sineLambda * sineLambda + temp * temp);
            cosineSigma = ss + cc * cosineLambda;

            sigma = Math.atan2(sineSigma, cosineSigma);

            var sineAlpha;

            if (sineSigma === 0.0) {
                sineAlpha = 0.0;
                cosineSquaredAlpha = 1.0;
            } else {
                sineAlpha = cc * sineLambda / sineSigma;
                cosineSquaredAlpha = 1.0 - sineAlpha * sineAlpha;
            }

            lambdaDot = lambda;

            cosineTwiceSigmaMidpoint = cosineSigma - 2.0 * ss / cosineSquaredAlpha;

            if (isNaN(cosineTwiceSigmaMidpoint)) {
                cosineTwiceSigmaMidpoint = 0.0;
            }

            lambda = l + computeDeltaLambda(eff, sineAlpha, cosineSquaredAlpha,
                                            sigma, sineSigma, cosineSigma, cosineTwiceSigmaMidpoint);
        } while (Math.abs(lambda - lambdaDot) > CesiumMath.EPSILON12);

        var uSquared = cosineSquaredAlpha * (major * major - minor * minor) / (minor * minor);
        var A = 1.0 + uSquared * (4096.0 + uSquared * (uSquared * (320.0 - 175.0 * uSquared) - 768.0)) / 16384.0;
        var B = uSquared * (256.0 + uSquared * (uSquared * (74.0 - 47.0 * uSquared) - 128.0)) / 1024.0;

        var cosineSquaredTwiceSigmaMidpoint = cosineTwiceSigmaMidpoint * cosineTwiceSigmaMidpoint;
        var deltaSigma = B * sineSigma * (cosineTwiceSigmaMidpoint + B * (cosineSigma *
                (2.0 * cosineSquaredTwiceSigmaMidpoint - 1.0) - B * cosineTwiceSigmaMidpoint *
                (4.0 * sineSigma * sineSigma - 3.0) * (4.0 * cosineSquaredTwiceSigmaMidpoint - 3.0) / 6.0) / 4.0);

        var distance = minor * A * (sigma - deltaSigma);

        var startHeading = Math.atan2(cosineU2 * sineLambda, cs - sc * cosineLambda);
        var endHeading = Math.atan2(cosineU1 * sineLambda, cs * cosineLambda - sc);

        ellipsoidGeodesic._distance = distance;
        ellipsoidGeodesic._startHeading = startHeading;
        ellipsoidGeodesic._endHeading = endHeading;
        ellipsoidGeodesic._uSquared = uSquared;
    }

    var scratchCart1 = new Cartesian3();
    var scratchCart2 = new Cartesian3();
    function computeProperties(ellipsoidGeodesic, start, end, ellipsoid) {
        var firstCartesian = Cartesian3.normalize(ellipsoid.cartographicToCartesian(start, scratchCart2), scratchCart1);
        var lastCartesian = Cartesian3.normalize(ellipsoid.cartographicToCartesian(end, scratchCart2), scratchCart2);

        //>>includeStart('debug', pragmas.debug);
        Check.typeOf.number.greaterThanOrEquals('value', Math.abs(Math.abs(Cartesian3.angleBetween(firstCartesian, lastCartesian)) - Math.PI), 0.0125);
        //>>includeEnd('debug');

        vincentyInverseFormula(ellipsoidGeodesic, ellipsoid.maximumRadius, ellipsoid.minimumRadius,
                               start.longitude, start.latitude, end.longitude, end.latitude);

        ellipsoidGeodesic._start = Cartographic.clone(start, ellipsoidGeodesic._start);
        ellipsoidGeodesic._end = Cartographic.clone(end, ellipsoidGeodesic._end);
        ellipsoidGeodesic._start.height = 0;
        ellipsoidGeodesic._end.height = 0;

        setConstants(ellipsoidGeodesic);
    }

    /**
     * Initializes a geodesic on the ellipsoid connecting the two provided planetodetic points.
     *
     * @alias EllipsoidGeodesic
     * @constructor
     *
     * @param {Cartographic} [start] The initial planetodetic point on the path.
     * @param {Cartographic} [end] The final planetodetic point on the path.
     * @param {Ellipsoid} [ellipsoid=Ellipsoid.WGS84] The ellipsoid on which the geodesic lies.
     */
    function EllipsoidGeodesic(start, end, ellipsoid) {
        var e = defaultValue(ellipsoid, Ellipsoid.WGS84);
        this._ellipsoid = e;
        this._start = new Cartographic();
        this._end = new Cartographic();

        this._constants = {};
        this._startHeading = undefined;
        this._endHeading = undefined;
        this._distance = undefined;
        this._uSquared = undefined;

        if (defined(start) && defined(end)) {
            computeProperties(this, start, end, e);
        }
    }

    defineProperties(EllipsoidGeodesic.prototype, {
        /**
         * Gets the ellipsoid.
         * @memberof EllipsoidGeodesic.prototype
         * @type {Ellipsoid}
         * @readonly
         */
        ellipsoid : {
            get : function() {
                return this._ellipsoid;
            }
        },

        /**
         * Gets the surface distance between the start and end point
         * @memberof EllipsoidGeodesic.prototype
         * @type {Number}
         * @readonly
         */
        surfaceDistance : {
            get : function() {
                //>>includeStart('debug', pragmas.debug);
                Check.defined('distance', this._distance);
                //>>includeEnd('debug');

                return this._distance;
            }
        },

        /**
         * Gets the initial planetodetic point on the path.
         * @memberof EllipsoidGeodesic.prototype
         * @type {Cartographic}
         * @readonly
         */
        start : {
            get : function() {
                return this._start;
            }
        },

        /**
         * Gets the final planetodetic point on the path.
         * @memberof EllipsoidGeodesic.prototype
         * @type {Cartographic}
         * @readonly
         */
        end : {
            get : function() {
                return this._end;
            }
        },

        /**
         * Gets the heading at the initial point.
         * @memberof EllipsoidGeodesic.prototype
         * @type {Number}
         * @readonly
         */
        startHeading : {
            get : function() {
                //>>includeStart('debug', pragmas.debug);
                Check.defined('distance', this._distance);
                //>>includeEnd('debug');

                return this._startHeading;
            }
        },

        /**
         * Gets the heading at the final point.
         * @memberof EllipsoidGeodesic.prototype
         * @type {Number}
         * @readonly
         */
        endHeading : {
            get : function() {
                //>>includeStart('debug', pragmas.debug);
                Check.defined('distance', this._distance);
                //>>includeEnd('debug');

                return this._endHeading;
            }
        }
    });

    /**
     * Sets the start and end points of the geodesic
     *
     * @param {Cartographic} start The initial planetodetic point on the path.
     * @param {Cartographic} end The final planetodetic point on the path.
     */
    EllipsoidGeodesic.prototype.setEndPoints = function(start, end) {
        //>>includeStart('debug', pragmas.debug);
        Check.defined('start', start);
        Check.defined('end', end);
        //>>includeEnd('debug');

        computeProperties(this, start, end, this._ellipsoid);
    };

    /**
     * Provides the location of a point at the indicated portion along the geodesic.
     *
     * @param {Number} fraction The portion of the distance between the initial and final points.
     * @param {Cartographic} result The object in which to store the result.
     * @returns {Cartographic} The location of the point along the geodesic.
     */
    EllipsoidGeodesic.prototype.interpolateUsingFraction = function(fraction, result) {
        return this.interpolateUsingSurfaceDistance(this._distance * fraction, result);
    };

    /**
     * Provides the location of a point at the indicated distance along the geodesic.
     *
     * @param {Number} distance The distance from the inital point to the point of interest along the geodesic
     * @param {Cartographic} result The object in which to store the result.
     * @returns {Cartographic} The location of the point along the geodesic.
     *
     * @exception {DeveloperError} start and end must be set before calling function interpolateUsingSurfaceDistance
     */
    EllipsoidGeodesic.prototype.interpolateUsingSurfaceDistance = function(distance, result) {
        //>>includeStart('debug', pragmas.debug);
        Check.defined('distance', this._distance);
        //>>includeEnd('debug');

        var constants = this._constants;

        var s = constants.distanceRatio + distance / constants.b;

        var cosine2S = Math.cos(2.0 * s);
        var cosine4S = Math.cos(4.0 * s);
        var cosine6S = Math.cos(6.0 * s);
        var sine2S = Math.sin(2.0 * s);
        var sine4S = Math.sin(4.0 * s);
        var sine6S = Math.sin(6.0 * s);
        var sine8S = Math.sin(8.0 * s);

        var s2 = s * s;
        var s3 = s * s2;

        var u8Over256 = constants.u8Over256;
        var u2Over4 = constants.u2Over4;
        var u6Over64 = constants.u6Over64;
        var u4Over16 = constants.u4Over16;
        var sigma = 2.0 * s3 * u8Over256 * cosine2S / 3.0 +
            s * (1.0 - u2Over4 + 7.0 * u4Over16 / 4.0 - 15.0 * u6Over64 / 4.0 + 579.0 * u8Over256 / 64.0 -
            (u4Over16 - 15.0 * u6Over64 / 4.0 + 187.0 * u8Over256 / 16.0) * cosine2S -
            (5.0 * u6Over64 / 4.0 - 115.0 * u8Over256 / 16.0) * cosine4S -
            29.0 * u8Over256 * cosine6S / 16.0) +
            (u2Over4 / 2.0 - u4Over16 + 71.0 * u6Over64 / 32.0 - 85.0 * u8Over256 / 16.0) * sine2S +
            (5.0 * u4Over16 / 16.0 - 5.0 * u6Over64 / 4.0 + 383.0 * u8Over256 / 96.0) * sine4S -
            s2 * ((u6Over64 - 11.0 * u8Over256 / 2.0) * sine2S + 5.0 * u8Over256 * sine4S / 2.0) +
            (29.0 * u6Over64 / 96.0 - 29.0 * u8Over256 / 16.0) * sine6S +
            539.0 * u8Over256 * sine8S / 1536.0;

        var theta = Math.asin(Math.sin(sigma) * constants.cosineAlpha);
        var latitude = Math.atan(constants.a / constants.b * Math.tan(theta));

        // Redefine in terms of relative argument of latitude.
        sigma = sigma - constants.sigma;

        var cosineTwiceSigmaMidpoint = Math.cos(2.0 * constants.sigma + sigma);

        var sineSigma = Math.sin(sigma);
        var cosineSigma = Math.cos(sigma);

        var cc = constants.cosineU * cosineSigma;
        var ss = constants.sineU * sineSigma;

        var lambda = Math.atan2(sineSigma * constants.sineHeading, cc - ss * constants.cosineHeading);

        var l = lambda - computeDeltaLambda(constants.f, constants.sineAlpha, constants.cosineSquaredAlpha,
                                            sigma, sineSigma, cosineSigma, cosineTwiceSigmaMidpoint);

        if (defined(result)) {
            result.longitude = this._start.longitude + l;
            result.latitude = latitude;
            result.height = 0.0;
            return result;
        }

        return new Cartographic(this._start.longitude + l, latitude, 0.0);
    };

    return EllipsoidGeodesic;
});