code: function(myPos, myVelo, targetPos, targetVelo ) {
      var distance = Math.sqrt(mf.lengthSquared(mf.sub(targetPos, myPos)));
      var approachSpeed = this.calcApproachSpeed(myPos, myVelo, targetPos, targetVelo);
      if( approachSpeed > 0.0 ) {
        return distance / approachSpeed;
      }
      else {
        return undefined;
      }
    }
docs: Calculates the arrivaltime of the target to my position.
  @method calcArrivalTime
  @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 time in which the target has reached me or undefined if not reachable.
  @for motionpredict