penumbra line, sunlight

gistfile1.txt

https://github.com/AnalyticalGraphicsInc/cesium/issues/4123

var viewer = new Cesium.Viewer('cesiumContainer');

var penumbraSunlightPolyline = viewer.entities.add({
    name: 'sunlight/penumbra polygon',
    polyline: {
        positions: Cesium.Cartesian3.fromDegreesArray([
            0, 0,
            1, 0
        ]),
        width: 2,
        material: Cesium.Color.YELLOW,
        show: true,
        loop: true
    }
});
var penumbraUmbraPolyline = viewer.entities.add({
    name: 'sunlight/penumbra polygon',
    polyline: {
        positions: Cesium.Cartesian3.fromDegreesArray([
            0, 0,
            1, 0
        ]),
        width: 2,
        material: Cesium.Color.BLUE,
        show: true,
        loop: true
    }
});
var penumbraVertexCount = 6;
var penumbraVertexRotation = 2*Cesium.Math.PI / penumbraVertexCount;
var simUpdateStep = 1; //update time step in seconds; will be scaled by clock multiplier
var sunRadius = 696.3; //mean radius in 10^6 meters
var earthRadius = 6.372797560856; //mean radius in 10^6 meters
var lastUpdateTime = new Cesium.JulianDate(0,0);
function updatePenumbraLines(clock) {
    //updating too often brings cesium to a halt
    if(Cesium.JulianDate.equalsEpsilon(lastUpdateTime, clock.currentTime, Math.abs(clock.multiplier)*simUpdateStep)) {return;}
    //sun position
    var spwc = viewer.scene.context.uniformState.sunPositionWC;
    var D = Cesium.Cartesian3.magnitude(spwc)/1000000.0; //distance from earth to sun in 10^6 meters
    if(D) {//prevent NaN errors
        lastUpdateTime = clock.currentTime;
        var sv = Cesium.Cartesian3.normalize(spwc, new Cesium.Cartesian3());
        //vertex rotation
        var q = Cesium.Quaternion.fromAxisAngle(sv, penumbraVertexRotation);
        var R = Cesium.Matrix3.fromQuaternion(q);
        //sunlight line
        var angle = Math.acos((sunRadius+earthRadius)/D); //sunlight cone inner half-angle
        var v = new Cesium.Cartesian3(0,0,1);
        Cesium.Cartesian3.cross(sv, v, v); //get vector orthogonal to sv
        var qs = Cesium.Quaternion.fromAxisAngle(v, angle);
        var Rs = Cesium.Matrix3.fromQuaternion(qs);
        Cesium.Matrix3.multiplyByVector(Rs, sv, v);
        var pos = [];
        var w;
        for (var i=0; i<=penumbraVertexCount; ++i){
            Cesium.Matrix3.multiplyByVector(R, v, v);
            w = Cesium.Cartesian3.clone(v);
            viewer.scene.globe.ellipsoid.scaleToGeocentricSurface(w, w);
            pos.push(w);
        }
        penumbraSunlightPolyline.polyline.positions = pos;
        //umbra line
        Cesium.Cartesian3.negate(sv, sv); //umbra cone points away from sun
        angle = Math.acos((sunRadius-earthRadius)/D); //umbra cone inner half-angle
        v = new Cesium.Cartesian3(0,0,1);
        Cesium.Cartesian3.cross(sv, v, v); //get vector orthogonal to sv
        var qu = Cesium.Quaternion.fromAxisAngle(v, angle);
        var Ru = Cesium.Matrix3.fromQuaternion(qu);
        Cesium.Matrix3.multiplyByVector(Ru, sv, v);
        pos = [];
        for (i=0; i<=penumbraVertexCount; ++i){
            Cesium.Matrix3.multiplyByVector(R, v, v);
            w = Cesium.Cartesian3.clone(v);
            viewer.scene.globe.ellipsoid.scaleToGeocentricSurface(w, w);
            pos.push(w);
        }
        penumbraUmbraPolyline.polyline.positions = pos;;
    }
}

//add the event handler
viewer.clock.onTick.addEventListener(updatePenumbraLines);