GPS accuracy and processing in Mavis

This is a short report about a survey campaign of several days with different copters and GPS. After processing the data of six adjacent flights in Mavis independently we analyzed positional accuracy.


The flights


 

ImageLoc

The flights were conducted using two of our copters – one with an u-blox M8N and the other with an M8T GPS. The survey period was 4 days. Six orthomosaics of the campaign were overlapping

Dataset Day time
A 3 10:40
B 1 11:20
C 4 12:00
D 4 10:20
E 4 11:00
F 1 10:00

Names
The orthomosaics were generated using direct georeferencing, i.e. without any RTK processing or ground control points. Hence, the final accuracy, or to be more precise the spatial offset between the maps, is a function of the accuracy of a single GPS and the image processing pipeline.

Since the flights were conducted over 4 days with different GPS and copter setups, the positional offset shows the overall GPS accuracy that can be achieved with M8 GPSs which we recommend for UAV setups. The processing chain was the same for all datasets.

Flight altitude was 50-60 m. Images were taken using Canon S110 cameras. The size of the survey locations ranges form 5 to 25 ha. The length of the entire area covered by the orthomosaics (from A to F) is 2.7 km.

 

The maximum spatial offset between two orthomosaics is 1.2 m. The average is 0.87 m.

Overlay Offset
 A vs B 0.8 m
 A vs C 0.6 m
 B vs C 1.2 m
 B vs D 0.4 m
 D vs E 1.1 m
 E vs F 1.1 m

This shows that when using u-blox M8 GPS high positional accuracies can be achieved even without RTK or ground control points. This is in accordance to previous tests where we compared several GPS against each other.

In general a large ground plane and a good shielding is recommended for best results.

However, the copter setup is crucial as are external factors such as the K-Index.

Roof2

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