function VelocityVectorProperty(position, normalize) {
  this._position = undefined;
  this._subscription = undefined;
  this._definitionChanged = new Event();
  this._normalize = normalize ?? true;

  this.position = position;
}
A {@link Property} which evaluates to a {@link Cartesian3} vector
based on the velocity of the provided {@link PositionProperty}.

@alias VelocityVectorProperty
@constructor

@param {PositionProperty} [position] The position property used to compute the velocity.
@param {boolean} [normalize=true] Whether to normalize the computed velocity vector.

@example
//Create an entity with a billboard rotated to match its velocity.
const position = new Cesium.SampledProperty();
position.addSamples(...);
const entity = viewer.entities.add({
  position : position,
  billboard : {
    image : 'image.png',
    alignedAxis : new Cesium.VelocityVectorProperty(position, true) // alignedAxis must be a unit vector
  }
}));