improve the heading

modules/math/heading.js

@@ -35,6 +35,11 @@ export default function heading(start, end) {
     v,
     new Cesium.Cartesian3()
   )
+
+  if (isNaN(vector.x) || isNaN(vector.y) || isNaN(vector.z)) {
+    return 0
+  }
+
   Cesium.Cartesian3.normalize(vector, vector)
   let heading = Math.atan2(vector.y, vector.x) - Cesium.Math.PI_OVER_TWO