R. Koehler

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  1. Thanks for your thoughts and input. Yes, I also saw the lack of any points being exactly on target. I'm still wondering how that might happen. For directions, I thing having the GNSS antenna on the rear of the drone is part of the answer. I agree that surveyed GCPs would be the best solution to this issue. As you also mention, a local real-time GNSS corrector system like RTK tailored for drone operations is an option. Either way means a significant increase in equipment and labor costs. I'd be interested to finding a way to include WAAS/SBAS signals to apply a real-time corrector. I'm still looking for that. It would also be nice to have a way to post-process the drone GNSS data (like most GPS receivers/software can do), though I haven't been able to find anything online to do this. If nothing else, a person might want to know the directional bias and perhaps find a way to account for this error. But for those that don't go either of these steps and just use the drone's position for aerial mapping/GIS, this is a serious issue to be sure. From my days as a surveyor for NOAA, the rule of thumb is that your positioning framework should be 10x more accurate than the final geo-spatial product. Using this as a guide, a 2-meter uncertainty in the framework would mean the final product accuracy would be only be good to 20 meters. Now we are talking something a bit more troubling.
  2. I'm new to this community so here's brief intro. I teach GPS for GIS at a local community college where I include a drone section for the class. Lots of student interest! I obtained my part 107 certification this past summer and just got a DJI Mavic Pro 2. My prior background was a hydrographic surveyor for NOAA where I established geodetic survey marks. Please take a look at my post on direction bias. I haven't found any online info about this. Thanks!
  3. Recently I wanted to confirm the positional accuracy of my DJI Mavis Pro 2. I placed the drone over a known NGS survey mark, then hovered at 2 then 10 meters above the mark. I took a total of 300 images to capture the GNSS latitude and longitude values (100 per height, with about 25 in each cardinal direction , N, E, S, and W) . The DJI Go app showed 17 to 20 GNSS satellites were being tracked. The results are shown below which show a clear directional bias in the positions. Has anyone else run into this? Thanks! Link to plot image. https://1drv.ms/u/s!AhKoglIEIVS6g5MzgvCkIu7YEfcm4w?e=BKC8G0