Some results from DGPS point measurements with a Stonex S9III GNSS DGPS receiver indicate an offset of 1.5-3 m to the Phantom 4 Pro ortho mosaic images. The relative accuracy is however much better. The Phantom 4 Pro derived ortho mosaic (without reference points) has a standard deviation of 0.31 to 0.36 m.
When comparing the overall positional accuracy of the reference points its surprising that the UTM coordinates that come directly from the Phantom 4 Pro are not far off: I measured 12 DGPS points and found that the offset is between 150 cm and 290cm (compare with Fig. 6).
RMSE between the Stonex S9III DGPS (SAPOS) measured points and the DJI Phantom 4 pro POI mode ortho image mosaic measured points is 1,98 m (stdev 0,31 m) and the RMSE between the Stonex Points and P4P NADIR mode ortho image mosaic measured points is 2,95 m (stdev 0,36 m). The difference is clearly also depending on overall atmosphere conditions and Stonex DGPS accuracy.
Fig. Comparison of measured DGPS Stonex GNSS points with in-Copter derived GPS geometry in POI ortho mosaic and with Nadir ortho mosaic processed in Agisoft in September 2017.
Using DroneDeploy and the POI mode of DJI.
Have been doing some leaf-off flights now in March on one of my favorite sites for complex tree crown point cloud mapping. To add to the leaf-on data from last autumn.
Fig.: Leaf-Off point cloud with combined height color coding and reflectance color coding.
This time I also checked the full automatic flight modi using the POI (Point Of Interest) mode from DJI and Drone Deploy with the P4Pro and the P3A.
Both work perfectly although I believe the POI mode can be dangerous when its done with low altitudes. You have to carefully check that the radius is free from obstacles when you define the center position, altitude and distance from center (radius) for the POI flight. When POI is started it begins with comparably low speeds. You can modify the speed setting when the POI mode started. Unfortunately you cannot modify this stetting before you start. Tuning the speed on an iPad or (even more difficult – on an iPhone) is kind of dangerous because you easily move the slide too much to higher speeds than wanted and the copter will immediately accelerate and start circling your POI object like crazy until you managed to move the slider to slower speeds. There is however always this stop button to kill the POI mode – this is handy and needed sometimes. When you press the stop button the copter stops the POI mode completely and waits for new commands.
Continue reading “Using DroneDeploy and the POI mode for automatic point cloud mapping”
Some thoughts on the copter data processing workflow now online here:
Copter Image Data Processing Workflow