How can I draw an arrow head at both ends of a polyline?

[eric-g-97477]

And for future reference… I did find this thread which briefly mentions creating a custom MaterialProperty which could be used with an entity…

Custom material on a Rectangle Entity

I am trying to add an Entity whose has several varying properties such as material (alpha, mostly) and rotation. RectangleGraphics has rotation covered, and works when I set the material to represent a texture.     viewer.entities.add({       name: 'Site Layer',       rectangle: {         coordinates: rectangle,         material: 'Image.jpg',         rotation: Cesium.Math.toRadians(13)       }     }); However, when I tried to implement transparency by using a custom Material (using http…