No GCPs ~ Matrice 600 vs Inspire 2 vs Mavic 2 Pro

Continuing the series on 3D Survey Mapping with various drones and cameras.

If you missed Part 1 of the first drone comparison of the Mavic 2 Pro and Inspire 2 you can read it here: https://conta.cc/2Y6fgxh


If you missed Part 2 comparing the M600, Inspire 2 and Mavic 2 Pro you can read it here: https://conta.cc/2K0pvzu


The Project Site (13.5 acres)

The previous two comparisons showed the RMSE values for the three different drones utilizing GCPs and checkpoints.

I was wondering what the RMSE values would be if there were no GCPs which would indicate the amount of image distortion throughout the model for each drone camera.

For the three drones used in this test the GCPS were unchecked then camera optimization was reapplied.

Here are the results.
This project site was flown with the Matrice 600, Inspire 2 and Mavic 2 Pro.
´╗┐The side by side results are shown below as processed through Metashape Pro.
Matrice 600 ~ Phaseone Camera
(55mm) 50mp
8280 x 6208 (px)
Sensor 44.0mm x 33.0mm
AGL 350'
FOV: (w) 279', (h) 210'
Neat area: (w) 195', (h) 84'
Speed: 10.7 mph
Capture rate 4 sec.
GSD: 1.03 cm
Flight time: 5 min
Flight app: GSP
# of images: 70
40% side, 70% front

Mavic 2 Pro

(10.26mm) 20mp
5472 x 3648 (px)
Sensor 13.2mm x 8.8mm
AGL 150'
FOV: (w) 193', (h) 129'
Neat area: (w) 77', (h) 39'
Speed: 8.8 mph
Capture rate 3 sec.
GSD: 1.08 cm
Flight time: 11 min
Flight app: Litchi
# of images: 220
60% side, 70% front
Inspire 2 ~ x5s

(15mm) 20mp
5280 x 3956 (px)
Sensor 17.3mm x 13.0 mm
AGL 200'
FOV: (w) 231', (h) 173'
Neat area: (w) 92'), (h) 52'
Speed 11.8 mph
Capture rate 3 sec.
GSD 1.33 cm
Flight time: 8 min
Flight app: Litchi
# of images: 147
60% side, 70% front
The following site (180 acres) was flown with the M600 Pro RTK with the GCPs turned off to test the positional accuracy of the RTK EXIF image tag and alignment processing.
Matrice 600 ~ Phaseone Camera
(55mm) 50mp
8280 x 6208 (px)
Sensor 44.0mm x 33.0mm
AGL 400'
FOV: (w) 279', (h) 210'
Neat area: (w) 195', (h) 84'
Speed: 10.7 mph
Capture rate 4 sec.
GSD: 1.03 cm
Flight time: 45 min
Flight app: GSP
# of images: 523
30% side, 60% front

Conclusion

The residuals above indicate that the Z values are unreliable without GCPs.

The X and Y values are better than the Z values which are close enough for an non-rectified orthomosaic if no horizontal measurements are needed to key features in the ortho.

I am a little disappointed in the RTK results with the M600. I have read and been told that no GCPs are needed with RTK. Each image EXIF tag might be more accurate to adjacent images however when the images are aligned there is still distortion without GCPs.

Without GCPs to a known datum, the processing software block bundle and least squares adjustment has no fixed position to constrain the model to.

Most of the mapping that I do is for 3D design level for engineers. The results have to be within ASPRS accuracy standards and constrained to a known datum.

Does RTK help with the accuracies and eliminate the need for GCPs? I am not convinced that they do, at least for 3D design level mapping.

For GIS Mapping RTK would be useful for results to a specific projection.

Is RTK worth the $5k+ price tag, you will have to be the judge on that. I don't think it is worth it. The RTK unit for the M600 sits in a box on my desk. I don't use it.

It really boils down to constraining the model to known positions (GCPs) on the ground to get the most accurate results.
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