I created these functions for a project of mine, see if they can help:

```
function arrowFromTo(latitude, longitude, height, elev, azimut, length, width, color){
latitude = Cesium.Math.toRadians(latitude);
longitude = Cesium.Math.toRadians(longitude);
var origin = new Cesium.Cartographic(longitude, latitude, height);
var originC3 = new Cesium.Cartographic.toCartesian(origin);
// Altitude (aka Elevation) and Azimuth can also be seen as Pitch and Heading, with Roll = 0:
var heading = Cesium.Math.toRadians(azimut);
var pitch = Cesium.Math.toRadians(elev);
var roll = 0.0;
var direction = new Cesium.HeadingPitchRoll(heading, pitch, roll);
////////////
var result = createROIfromRotation(origin, direction, length);
////////////
drawLine(originC3.x ,originC3.y, originC3.z, result.x ,result.y, result.z, width, color);
}
```

```
function drawLine(x1,y1,z1, x2, y2, z2, width, color) {
var origin = new Cesium.Cartesian3(x1,y1,z1);
var dest = new Cesium.Cartesian3(x2,y2,z2);
viewer.entities.add({
polyline: {
positions: [
origin,
dest
],
arcType: Cesium.ArcType.NONE ,
width: width,
material: new Cesium.PolylineArrowMaterialProperty(color)
}
});
}
```

```
function createROIfromRotation(position, rotation, length) {
// position: Cartographic - {latitude, longitude, altitude})
// rotation: HeadingPitchRoll - {heading, pitch, roll}
// Based on answer found here:
// https://stackoverflow.com/questions/58021985/create-a-point-in-a-direction-in-cesiumjs
var cartesianPosition = Cesium.Ellipsoid.WGS84.cartographicToCartesian(position);
rotation.heading = rotation.heading - Cesium.Math.toRadians(90);
var referenceFrame1 = Cesium.Transforms.headingPitchRollQuaternion(cartesianPosition, rotation);
var rotationMatrix = Cesium.Matrix3.fromQuaternion(referenceFrame1, new Cesium.Matrix3());
var rotationScaled = Cesium.Matrix3.multiplyByVector(rotationMatrix, new Cesium.Cartesian3(length, 0, 0), new Cesium.Cartesian3());
var roiPos = Cesium.Cartesian3.add(cartesianPosition, rotationScaled, new Cesium.Cartesian3());
return roiPos;
}
```