If you plan to fly a site survey at a mission height below 260ft (80m), you must change your other mission settings to produce usable data.
Mission Height
The minimum mission height the Phantom 4 RTK can fly is 82ft (25m). For drones that use DJI Pilot 2, including the Matrice 300 RTK and Mavic 3 Enterprise, the minimum mission height is 40ft (12m). Flying this low results in very high-resolution images and a small ground sample distance (GSD). Check out our GSD Calculator to see what the GSD will be for your mission. However, we don't recommend flying any lower than 120ft (36m), unless airspace restrictions or other situational factors require a lower mission height. When your mission height is restricted by airspace, plan a buffer of at least 1m below the ceiling. For example, if the flight ceiling is 100ft (30m), you should fly at 98ft.
Overlap
Increase the image overlap to at least 80%, both front and side. The lower the mission height, the higher the overlap rate should be. Increasing the overlap makes you far less likely to have holes in your final site model. However, increasing the overlap will increase the mission time, so be prepared to change batteries during the mission.
Note: To get high-accuracy PPK geotags, you must have at least 10 minutes of mission time per battery.
Speed
Flying close to the ground makes you far more susceptible to motion blur. Therefore, you should decrease the speed of the drone.
Decreasing speed at lower heights is important for image quality and your drone's protection. You should fly more cautiously because there are more obstacles when you fly closer to the ground. Furthermore, your visual line of sight (VLOS) may be compromised when flying low.
Take-off Point
Try to take off from the highest point on the site. This helps prevent holes in your final model and ensures you have VLOS to your drone.
Other Settings
You should not need to change other mission settings when flying at low heights.
I still can't do it!
We wrote these articles to equip you with everything you need to get the job done on your own, but we understand that sometimes this isn't sufficient.
If you're stuck, the Propeller hardware support team may be able to help. You can contact them by emailing hardwaresupport@propelleraero.com.au.
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