code: function(myPos, myVelo, targetPos, targetVelo) {
      var posDiff = mf.sub(targetPos, myPos);
      var veloDiff = mf.sub(targetVelo, myVelo);
      var approachSpeed = mf.dot(posDiff, veloDiff);
      var posDiffLength = Math.sqrt(mf.lengthSquared(posDiff));
      if( posDiffLength <= 0.0 )
        return 0.0;
      return -approachSpeed / posDiffLength;
    }
docs: Calculates the approachspeed of the target to my position.
  @method calcApproachSpeed
  @param myPos {Vector3d} The position of me.
  @param myVelo {Vector3d} The velocity of me.
  @param targetPos {Vector3d} The position of the target.
  @param targetVelo {Vector3d} The velocity and direction in which the target is moving.
  @return {Number} The speed at which the target is approaching.
  @for motionpredict