Mapping with the DJI Mavic Mini and Dronelink
As any "normal" scientist, part of my vacation was dedicated to learning something new. In this case I wanted to enhance my piloting skills by learning how to map with an entry level drone, the DJI Mini, using the software Dronelink (iOS). Technically, the DJI Mini is not a mapping drone as it lacks onboard waypoint capabilities, which are the foundation for the drone to follow a specific route. However, Dronelink has addressed this issue taking advantage of the open architecture of the Mini, and creates a virtual stick, where specific commands are sent to the drone in real-time, and simulates how a human pilot would use the control sticks to remote control the flight direction and camera parameters...pretty cool!
The area for this mapping excercise was a small piece of land I own in Atenas, Costa Rica, of approximately 1.25 hectares (~3 acres). The topography of this land is a combination of flat and very irregular areas, which makes it nice for producing both an orthomosaic and a 3D point cloud.
Given that I have significant experience with the use of drones for different research applications, I can say that Dronelink provides a fairly easy use online interface (https://app.dronelink.com/login), which is suitable for proper mission planning. To be able to use the mapping function, I purchased the Elite plan (see price and supported drones here https://app.dronelink.com/pricing/hobbyist/compare). Once the mission was properly planned, the Dronelink Flight app (iOS) was used. The following figures show the online planned route, and the estimates for time and number of photos. A really cool feature of Dronelink is that it provides a comprehensive preview of the mission. The following figure shows the online interface map, parameters used, and the estimates for the mission.
Before showing the results, the main challenge while flying the mission was that my initial position for taking off was in a plateau area, which I chose at first because it was higher in elevation than the area I was mapping, and technically the drone was within line of sight at all times. However, I had a disconnection error between my fight controller and the drone, which I solved by first not panicking :) , and then by calmly allowing Dronelink to cancel the mission (it takes a few seconds), which allowed me to bring the drone back to the take-off point manually. My last attempt after few failed trials, was to move the take-off point within the flight planned area, which actually worked really well. The fun part is that this last attempt finished a couple of minutes before it started raining!
Once the photos were acquired, I uploaded them to Pix4D cloud (https://cloud.pix4d.com/) for processing. Here are the two main results that I planned for, the orthomosaic for the area as well as a screen capture of the 3D point cloud. Feel free to access and play with the 3D point cloud here.
A main aspect to notice in this orthomosaic is some blurriness, which might be the result of the photo quality and need for better camera parameters (e.g. faster shutter speed). Also, although it was not very windy, there was some wind at some points during the mission, which also affected the photo quality, and resulted in unresolved pixels, as noticeable by the black pixels. However, for a non-professional system, and inexpensive flight control software, I consider this to be a very good product. Bear in mind that I didn't use ground control points to evaluate the positional accuracy of the final product. Still I could use a map like this for baseline planning (e.g. canopy delineations, open areas vs vegetated areas).
Overall I was very excited about the quality of the 3D point cloud, with nice definition of the tree canopies, and visible changes in terrain elevation, not bad at all for such as basic system. In conclusion, I learned a new few things, and, more importantly increased my confidence in flying this drone. I also learned the very basics of Dronelink, which for sure I would like to explore more in the future. Thanks to @tutavenok for the topper image!
Check out my Essential Costa Rica aerial video also filmed with the Mavic Mini!