I live in Las Vegas Nevada. Here in the valley we are surrounded by mountains so it is very easy to find yourself above 500 meters. I recall a flying session at RedRock Canyon where i took off from Calico Tanks Trailhead and followed a gradual incline as I followed Turtlehead Peak. Before I knew it, my Mavic Platinum was telling me I was 400 meters up when i was actually just 50 feet from the ground.
I was a new pilot then and fearing what could happen should return home kick in 2 miles from where I took off I turned around and headed back. I think DJI should be able to GEO fence altitude restrictions within certain areas while leaving secluded areas open for free flight to higher altitudes. Maybe not, but it is very easy to find yourself higher than 500 meters in an area like Las Vegas.
On another flight later that day I flew back into IceBox canyon, a winding spectacle of rock. If anyone knows anything about flight around rocks that are hundreds of feet high, they know there is no penetration and your signal will be gone almost instantly should you turn a corner. This happened to me and RTH kicked in. The Mavic doesn’t return the path in which it came when RTH kicks in. It climbed to my specified RTH altitude of 40 meters and began flying the most direct rout to the takeoff area. I was in horror as I thought i lost my drone 1/2 mile into this huge canyon.
I lost everything in an instant and I could not even hear it. As I proceeded back into the canyon about a quarter mile, boom! My signal returned. I could not see or hear the drone from the ground nor could I recognize where i was from the drones camera. I stood still and listened as it headed home to the launch location. Eventually a could hear it pass over but it was too high to see. I began following the sound out of the canyon and eventually spotted it as it began to descend. I recovered it. I went home and watched the footage the drone continued to record. It was only then that I realized how close to loosing it I was.
When the drone instantly lost signal in the rock, RTH kicked in. The drone ascended as if was climbing steps until it cleared the top of the canyon and proceeded to the RTH spot. Each time the drone would come within a few feet of the canyon, stop and ascend on 3 different occasions. At its highest altitude it reached over 1000 feet before it cleared the canyon. I was in my first ten flights and I learned a lot that day but again had the canyon been higher than 500 meters I could have lost my drone. Thank goodness it wasn’t. It was that day that I learned the drone measures its altitude based on where it took off, not where its at.
Peace.