[GIS] Arcs (Circle Segments) in Cesium

cesium

Cesium polylines follow the curvature of the earth, between two points, by default. How do I make arcs, which go above the ground, like in this example?

http://armsglobe.chromeexperiments.com/

Best Answer

From https://groups.google.com/forum/#!topic/cesium-dev/anp15p-DIew

function addLines(pointA,pointB){ 

var earth = Cesium.Ellipsoid.WGS84;
// start and end points on the surface of the earth 
var startPoint = earth.cartographicToCartesian(Cesium.Cartographic.fromDegrees(pointA[0][0], pointA[0][1], 0.0)); 
var endPoint = earth.cartographicToCartesian(Cesium.Cartographic.fromDegrees(pointB[0][0], pointB[0][1], 0.0)); 


// determine the midpoint (point will be inside the earth) 
var midpointCartesian = startPoint.add(endPoint).divideByScalar(2.0); 

// move the midpoint to the surface of the earth 
earth.scaleToGeodeticSurface(midpointCartesian); 

// add some altitude if you want (1000 km in this case) 
var midpointCartographic = earth.cartesianToCartographic(midpointCartesian); 
midpointCartographic.height = 1000000; 
midpointCartesian = earth.cartographicToCartesian(midpointCartographic); 

// create a hermite spline that goes through these three points 
var hermiteSpline = new Cesium.HermiteSpline( [ 
    {point: startPoint, time: 0.0}, 
    {point: midpointCartesian, time: 0.5}, 
    {point: endPoint, time: 1.0} 
]); 

// create a 20 point polyline that follows the spline 
var polylinePoints = []; 
for(var i=0; i<20; ++i) { 
    polylinePoints.push(hermiteSpline.evaluate(i/20)); 
} 

var polylineCollection = new Cesium.PolylineCollection(); 
var polyline = polylineCollection.add(); 
polyline.setPositions(polylinePoints); 

var primitives = widget.scene.getPrimitives(); 
primitives.add(polylineCollection);
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