If the focus of your survey is primarily the fidelity of the DSM (topography), then you want to use the nadir mission type.
If the the aesthetic of the 3D model is the primary goal, then the oblique mission is correct.
M4T RTK accurate or not ..
- Thread starter Mflyer
- Start date
If the the aesthetic of the 3D model is the primary goal, then the oblique mission is correct.
Thanks. In this case the focus of the survey was to test the accuracy of M4T with RTK (I've used Base+Rover approach - DJI RTK3 + M4T). Because I've seen here different results from what I've obtained I was wondering where I was wrong.
At this point in the state of the processing technology, nadir image sets provide more accurate z values.
@jaja6009 error results for z on the M4T / Oblique without GCPs was over 1 foot. So worse than your 20cm. With GCPs, it dropped to .7 feet (21.34cm)
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I refer to this test
Test 1 Nadir Images with Altitude Optimization, 5 Check Points, No GCPs.
X: 3.14 cm, Y: 1.95 cm, Z: 8.14 cm Total: 8.93 cm
Test 2 Smart Oblique, 5 Check Points, No GCPs and we have a winner!
X: 1.98 cm, Y: 1.98 cm Z: 3.26 cm Total: 4.29 cm
Test 1 Nadir Images with Altitude Optimization, 5 Check Points, No GCPs.
X: 3.14 cm, Y: 1.95 cm, Z: 8.14 cm Total: 8.93 cm
Test 2 Smart Oblique, 5 Check Points, No GCPs and we have a winner!
X: 1.98 cm, Y: 1.98 cm Z: 3.26 cm Total: 4.29 cm
I would consider that result, i.e that the smart oblique was better, as an anomaly comparing it to all of the other tests. Not the standard. Your own text confirmed that the nadir set produced better results. You need not take my word for it. Do a dozen more tests on your own and confirm it for yourself.
Thank you. This is because oblique images (from Smart oblique) "confuse" more the photogrammetric process than just a few obliques in the "elevation optimizatione" mode ? Would it be better using the M4E ?
I'm not sure as to the "why". It may be that there are more variables for the processor to deal with using obliques compared to nadir images. Less similarity between potential tie points for example. But I don't really know.
Over all, the M4E would be a better platform if topography is the goal. If all else is the same, position accuracy, and image time stamping, etc., the M4E has a global shutter. But no thermal, obviously.
Over all, the M4E would be a better platform if topography is the goal. If all else is the same, position accuracy, and image time stamping, etc., the M4E has a global shutter. But no thermal, obviously.
I used the Smart Oblique where the drone takes several images for each position, a nadir and several obliques.
You used the 5 Flight Lines Oblique.
What software are you using for processing?
And I don't really have any insights yet as I am still testing by trying to map different areas.
When I run the data in Agisoft Pro, Pix4Dmapper and Drone Deploy, the results are very similar.
The 4E is going to be the better mapping drone period. The camera is much better in every aspect. Its just providing the photogrammetry software with more and better information in each image.
I still have to map 2 more areas, at school and my beach project. I will try to have the 4T map both to see how it fares.
I really would like to know from DJI engineers why the 4T fares worse in mapping. It seems like it is something more than just the mechanical shutter. The Autel Evo 2 with RTK module obtained survey grade results and lacked a mechanical shutter.
Also the wording from DJI on mapping with both leaves me scratching my head, "DJI Matrice 4E supports precise mapping after enabling RTK function. Equipping DJI Matrice 4T with the RTK module can’t guarantee the final precision."
It says equipping the 4T with an RTK module even though it is permanently affixed.
I just checked, the M4T's camera is not calibrated as Agisoft does not prepopulate the camera calibration, while the M4E does. But when I ran my tests, I did not use this information. I am rerunning the M4E at 15mph nadir with Altitude Opt using the precalibration for the camera to see what it does.
I used the 5-direction mission because the single-direction (with several images on the same position) was moving too far away from the area of interest, and honestly I don't why (maybe to obtain better results in Z?).
In any case, I’ll run some additional tests to better understand the differences between the two approaches.
Thank you for your input. I really appreciate it.
Of course, the M4T is not designed specifically for mapping and it definitely can’t operate at the same altitude (for the same GSD) and speed as the M4E. However, with a few adjustments, such as reducing flight speed and flying at a lower altitude, it’s still possible to achieve interesting mapping results with a good GSD. That said, I believe it’s always best practice to use ground control points (GCPs) and include additional check points for proper validation.
Thank you for the comparison tests you’re carrying out between the M4E and M4T. Let us know your results.
I reran the M4E now using the prepopulated camera calibration and the results in RMSE were about the same.
Also the adjusted camera calibration was about the same, so Agisoft ended up with a very similar camera calibration on its own, without using DJI's calibration as a starting point. Alexy from Agisoft recommends not using the prepopulated camera calibration so that is how i process it.
Agisoft also updated their FreshDesk instructionals and now has camera calibration recommendations for the M4E.
Also the adjusted camera calibration was about the same, so Agisoft ended up with a very similar camera calibration on its own, without using DJI's calibration as a starting point. Alexy from Agisoft recommends not using the prepopulated camera calibration so that is how i process it.
Agisoft also updated their FreshDesk instructionals and now has camera calibration recommendations for the M4E.
