RTH altitude when Mapping hill with AGL altitude reference
What will the RTH flight path be when using Mapping function with Terrain Follow AGL after the drone has finished mapping flight plan and gained significant elevation during the mapping flight of a hill. Tried viewing in Mission Preview but its not showing the RTH flight path.
Planning on mapping a hill that has a base, takeoff elevation of 600' MSL and top of hill is 1200' MSL where the mapping plan will complete. Drone flight level Altitude of 200' with Terrain Follow AGL. Current RTH altitude is 300' set in DJI. When the mapping is completed at the summit of the hill, aircraft will be at approximately 1,400' MSL
What MSL or AGL elevation will the drone reference when RTH is initiated at the summit of the hill? I was hoping it wouldn't reference the takeoff elevation of 600' MSL and descend into the ground. Currently Action on Finish is set at none until I have clarity on RTH flight path if RTH is selected upon completion of mapping flight plan.
Using a DJI Phantom 4 Pro V2
Thank you,
Kris
Comments
16 comments
It works the same as when using the DJI app. The drone will not descend when RTH is activated. It will either stay at the current altitude if it is higher then your set RTH in DJI app and return horizontality then land, or if it is lower then your set RTH altitude then increase up to that altitude and then return. The drones RTH altitude is based on your original ATL/ launch location altitude.
My suggestion is to add a simple path component at the end of map. You can add AGL markers along the path every so often while returning back. Depending on the distance and incline of the hill, it may need several markers or more to keep it roughly below the 400’ AGL ceiling. Give it a try and run it on Google Earth first to see how it looks then make adjustments to the map portion and/ or return path. Also need to realize that the maps terrain follow is similar to the AGL function but still uses ESRI data which isn't at every point along the path but rather every 30m of horizontal distance travelled. So running it on Google Earth will give you a good idea if the mapping will work correctly depending on the steepness of the elevation change. Seems like it may be difficult or a lot or work to ensure it doesn’t crash. Good luck and enjoy.
Mike…..
Mike,
Thanks for the RTH info. This makes sense and you have a good idea adding a path component at the end with AGL markers. I just upgraded to the growth plan from the basic mapping plan to allow for AGL altitude flights for flying map plans with significant elevation throughout the flight plan so adding components is a new process for me, but seems like a logical and safe solution. Appreciate your feedback and knowledge.
-Kris
Your welcome. I use AGL markers a good amount of the time because I live in a very rural area with rolling hills that go up and down a lot. Always check Google Earth with Amy plan I want to create where the elevations change a lot to see the hills much easier. Then run it and add markers at the higher elevated hills to make sure it ascends up at those locations. I’m not too worried about the lower elevation areas because it won’t run into a hill if it runs a bit higher up. Works really great.
Good luck. Mike…..
Mike,
One more question…. This flight has duration that will necessitate a battery swap. Is there a way to simulate the flight path of the RTH & return to flight plan for battery swap?
Not sure about that. Jim may be able to help with that.
I’m fairy sure when I’ve done battery swaps it always ascended up first to the previous altitude it was last at then flies horizontally to the last paused location. Otherwise the drone would never know how to get back safely.
Unless you paused the mission at a lower altitude than yourself, in which case it will do the reverse. In these scenarios it is always safer to fly it back to the resume point manually.
Thanks Jim and Mike.
Makes sense to fly it back up to the resume point manually.
Here is a link to the tentative flight plan:
https://app.dronelink.com/aggregate-resource-industries--inc-/my-first-project/plan/Xs3j5BPdi5YjNtQRjHQd/AOxVGFyDFYE6nor4WaU9
Open to suggestions if there is a better method to flight planning this location & attempting to bring back the drone safely. I'm running a PPK GPS system onboard for generating survey grade mapping so looking forward to using the AGL flight planning to improve the imagery but not sure how to test with out real world flight. Might grab a donor drone without the GPS gear onboard for test flight. Thanks.
Hi Kris. I ran it on Google Earth and it looks good. Also I did a 3D preview in the Native app to see what the path Looked from ground level and it I see no issues. You can start the mission and keep an eye on the screen and pause at any time during the mission if it looks like there is any issue. However, at 250’ AGL altitude you should have have no problem.
Enjoy, Mike…..
Jim/Mike,
Update on the AGL flight with approximately 850' of surface elevation gain from takeoff location.
Started flight from takeoff location at base of hill with 375' AGL flight level to be safe so I had some room to work with if need.
Flight paused once drone reached 400' ATL and I had to go into the DJI app and increase maximum flight altitude to compensate for the 375' AGL flight level and the 850' of elevation gain that the flight plan was covering.
2/3 through the flight, RTH activated and drone returned at the current flight level and descended once above Home Point.
Upon replacement of battery, drone ascended back to previous elevation where RTH was activated and drone completed mission.
At completion of the flight plan, drone returned home at the flight level that the mission completed.
In summary, Drone Link worked amazing. I would highly recommend starting the approach of the flight plan at the apex of the flight plan elevation so that when the RTH is activated, both for battery swap and completion of the flight plan, the RTH elevation is at a lower altitude closer to the home point of base of the hill. My approach point was near the base of the hill and flight completed near the apex of the hill and both of my return to homes and return to finish the flight plan after battery swap exceeded the 400' AGL and I will be sure for future flights to start from the apex and work the flight path down the hill in order to not exceed the 400' AGL.
Thanks again for your assistance.
Kris
Glad to hear it worked as great. Amazing App and so much you can accomplish. The max altitude reached makes sense since these drones aren’t spot on. The Altimeter, Barometer, GPS etc, have an accuracy of approximately + or - 4M. Since you know you are maintaining at or below the 400’ AGL it may be better just to set the Max altitude in the DJI app well above the 400’ needed to alleviate any future issues.
Enjoy Kris.
I usually have my max altitude set MUCH higher than 400'.
Remember that setting it in the DJI app it is not really AGL - it is above take off. If you set it for 400ft, and have a shoot in a valley with a 200ft climb on each side and need to follow the terrain (which I have done), your mission will fail unless you adjust for it.
Add in that AGL needs to take into account buildings and other things and setting the max altitude above 400ft is, IMHO, legitimate as long as you know what you are doing.
Thanks Barry,
Yes, I learned today that the DJI Max Flight Altitude setting is ATL so felt comfortable, as you and Mike recommended, increasing the DJI Max Flight Altitude setting to accommodate the terrain variable above takeoff elevation.
One other learning lesson today, using the map function with variable terrain, where terrain + AGL flight level exceeds 400' from Home Point elevation, I would not likely select the RTH upon completion of the plan. Instead as Mike recommended earlier, set a component path with AGL elevation markers for the RTH as a safe path home after completion of the map, or fly it back home manually.
Happy New Years!
-Kris
Kris Jeremiah
100% flying back manually would be best in situations where the terrain is variable.
But...I have another crazy idea (depending on the type of plan you are on).
If your plan is suitable for conversion to onboard waypoints (https://www.youtube.com/watch?v=4F-W4HKJlmA) then there is an undocumented feature there. If you pull back on the right stick the drone will follow the path in reverse, with speed varying by how far back you pull the stick. You can literally hold back on the right stick and have it return home knowing that it will follow the path it took to get there, which you now know to be safe.
That's probably overkilling it...but I have had situations where I have done that and it felt nice knowing I was safe :).
That is very good to know Barry! Thank you for the information on this feature.
If you do that, then you definitely need to manually fly it back to the resume point as the resume point will be a negative altitude.
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