I have been challenged for a long time with creating Low Level Planned Mission using the Hub that will actually work. However, I may have found a fix.
I flew a DJI Mini 2 and a Mavic Air 2, but my Phantom 4 V2 needs new batteries and was not flown during my test.
My first step was to plan a Mission in the Hub to follow an almost straight line in the center of a 2 lane road. I set several Way Points and set the Altitude to be 12 feet above my takeoff location on the street, I set my cruising speed to 4.3 mph and the final step was to have my drone fly at +90 degrees (sideways) as drone flew the path. I saved the Mission and then uploaded it to my tablet while on location. I stated my Mission and at the First Way Point my drone was 10 to 12 feet away from my programed Path. As this parallel Path would have flown my drone into trees and street signs, I just went home.
My second step was to go out to a large park with lots of open spaces. I placed 3 bright orange vests on the ground in the form of a triangle and they were about 100 feet away from each other. I selected the Way Point fly option to build a mission in the field on location. I walked my drone to each location and added each Way Point over the orange vests and Saved the Mission. With the Mission Saved I then set my air speed of 4.3 MPH and altitude at 10 feet for each Way Point so that they all matched. I flew the Mission with no issues and the drone flew directly over the vests as I wanted. I changed the altitudes several time and each flight was on target.
Conclusion
If I am flying a Low Level Mission with Way Points, then to be the most accurate I need to do it on location where I have total control and the GPS Location will be on target. While I did not set any Points of Interest during my flights the course was correct and SAFE. The drawback is that it takes extra time to setup and uses more drone battery time. I could go a day ahead of the shoot to build my Mission, but I need to make sure I am doing it at the same time of day so the GPS Satellites will be in the same location for my actual flight.
I am not sure if anyone else has had this same issue or maybe have another work around, but I would love to hear.
While a GPS location can be specified with great precision, the accuracy of flying to that GPS location is something less than perfect. Simply stating the accuracy for GPS can be difficult because there are many different types of GPS and many things that affect its accuracy. This is probably why one finds so many different GPS accuracy values quoted on-line.
Smartphones tend to use assisted GPS (A-GPS) which combines traditional GPS signals with cellular network data to increase the location accuracy. Therefore, smartphone position accuracy is generally better than that of devices using standard consumer GPS.
Like many consumer devices, DJI drones use what is called “Consumer GPS”. Depending on your source, the accuracy of consumer GPS implementations is anywhere between ± 3 to 8 meters (10 - 26 feet). However, DJI states the horizontal positioning accuracy of their older drones to be around ± 1.5 m (Mavic 2, Air 2s) and their newer drones to be ± 0.5 m (Mini 3, Mini 4, Mavic 3). I have flown literally 100s of waypoint missions and DJI’s stated accuracy corresponds well to what I have experienced when flying and repeating my waypoint missions. I have never experienced a waypoint mission to be anywhere near 8 meters (26 feet) off of the drone’s intended course. However, on one occasion, I set up a mission to fly down the center of a road. I configured the mission using Litchi’s Mission Hub. When flying the mission, the drone would have flown around six feet off the road’s center line. In this case I had to manually adjust the waypoints at the flying location to get the drone to fly down the center. When looking at the adjusted mission in the Litchi app, it looked like my flight path was well off the center line of the road. I never did any further testing. It would be interesting to see if this error was consistent from one day to the next or from one location to the next.
Please understand I did not and am not implying the Litchi failed in any way. I know I am reaching out to mutiple GPS Satellites for locational service and when flying in wide open skies and the drone is reading the information without any issues when flying free, However, I needed a way to do some work that would be more on a Hollywood style and none of my drones allow for a separate camera operator and drone pilot. The low level presets seem to help me work my mission more safely and with better accurately.
Since the position of GPS satellites is always changing, it would be interesting to see if you are consistently 10 to 12 feet off the center of the road. I have not tested this myself. It is possible (and this is just a guess) that on another day with a different satellite configuration in the sky your results might be different. Let us know if this discrepancy is something you can easily replicate or if it is just a one-time occurrence.