For the application of the autonomous guidance of a quadrotor from confined undulant ground. terrain-following is the major issue for flying at a low altitude. This study has modified the open-source autopilot based on the integration of a multi-sensor receiver (a Global Navigation Satellite System (GNSS)). a Lidar-lite (a laser-range-finder device). https://ashleyshomestores.shop/product-category/twin-mattress-and-pillow-2-cn/