Hotspot Effects in Micro Copter Data

A shots from last year vegetation point cloud mapping in Brandenburg. Strong Hotspot-Effect visible with easily visible shadow projection of the quadrocopter shape on the tree crown texture. Nice example of this direct back-reflection effect on vegetation (crown surface in this example), although you can also clearly see the same effect on the grassland vegetation in the neighborhood of the tree crown.



Absolut Accuracy of the Phantom 4 Pro Ortho Mosaic

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.

“DJI GS Pro” – Ground Station Testing

Some tests using the DJI GS Pro (Ground Station) software for automatic flight programming with the Phantom 4 Pro.

New flight campaign at the Kuckenburg spot (Sachsen-Anhalt) finished with two different flight altitudes using DJI GS Pro – mapping the open archaeological excavation site of medieval church now in September 2017. This worked flawless – the only problem: you kind of need a mobile connection with your iPad. Since DJI GS is an iPad-only software I used a hotspot from the iPhone to bring the iPad online. Its not perfect but it works. Overall I find DJI GS Pro to be more easy to program and to setup than Drone Deploy. The interface has more option to setup – so it is at first more complex but it integrates into the DJI Go App and so far my impression is that it is not giving these unexplained copter start problems that Drone Deploy sometimes showed. GS also seems to be less integrated into a subscription model and looks like a standalone software solution – though a DJI account is needed. I havnt tested capturing DNGs. Its not a direct option as far as I can see – this could be a limitation. You can easily modify exposure times and f-stop numbers even when flying to geht sharper shots. There is however so far no option to switch from JPEG to DNG. As this is usually only limited by bandwidth it could be an option that is available when you decrease the flight speed (leaving enough time between exposures) – so not tested yet.

As an in-App purchase you also can automatically do POI flights – this is very handy for these dense point clouds of single objects and its not so straight forward to do this in manually POI mode as part of the DJI GO software (though also possible).

DJI GS Pro however has some strange ways to handle waypoints when you use the hover method but once you understand where the problem is (the number of waypoints is restricted to 99) – it works nicely. DJI GS Pro also comes with different modi – “Virtual Fence” is very nice for training and restricting the flight space, “3D-Map Area” is for mapping of larger areas and “3D Map POI” is for these POI flights where you want to map 3D object structures and where you have enough space between objects to create some kind of circumnavigation.

The full manual goes here:

Some shots from the Kuckenburg flight campaign with 500 DNG shots and approx. 50Mio and 80Mio points in different dense point cloud calculations with Agisoft. As we don’t have a SAPOS subscription for “Sachsen-Anhalt” no DGPS points were measured. However some fixed points from the FSU Jena excavation team will be used.



New UAV regulations in place and active

The new UAV regulations are now active in Germany! For commerical and research flights things are more simple now for copters below 2kg. There is now a general allowance in place for the full federal region of Germany for UAVs below 2 kg (with the restricted regions as listed in the regulations). For copters with more weight a specific training certificate is needed and up from 5kg you need an allowance of the regional  aeronautical authority.


Using DroneDeploy and the POI mode for automatic point cloud mapping

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”

Phantom 4 Pro arrived

The Phantom 4 Pro arrived – first integration tests started and I am testing the image quality of the 1-Inch sensor – at least from my perspective the most important part of the new P4 series. Especially comparing dynamic range and sharpness to the tiny P3A sensor/lens combo and systems will be interesting (which is similar to the original P4 sensor).