Levels, and RTK, if you want to do this for academic purposes, leveling the targets and then surveying them with RTK for horizontal is the best way to do it. Vertical is always the control and it's more difficult to acquire precisely than horizontals. Levels are the key. The R12 is more than capable of getting it tight horizontally but it's restricted by the Geoid Model for vertical. If for some reason you wish very tight horizontals, do it static, with redundant occupations.?ÿ
less than .05' with drones,,,,,,,,, haven't seen that.?ÿ
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if the boards need to stay down for a while, rather than just for the day, then the 18 inch boards stand up better to wind, etc. than 2 ft. ones. If there's a lot of vegetation it's also easier to get the smaller size board to sit flat. Same comment applies if the ground has quite a slope on it.
We are using the boards for main control, but when we have been working with a manufacturer on test surveys for a PPK aircraft we found that the boards do improve the overall results. More importantly, if anything goes adrift with GPS signals then the boards provide a fall back so the project can be recovered.
The gsd of the Wingtra / Sony Rx1RII at 400' agl is 0.05ft.?ÿ I'd like to see how close I can get to that.?ÿ This will be an interesting exercise for sure.
I'm only using the targets as independent check points.?ÿ All of the processing will be performed with PPK processed geotags only (x, y, z, omega, phi, kappa).?ÿ That is part of the study, to see what parameters affect accuracy, and ultimately how accurate is PPK-only for this particular UAS.
Guess that drone figure is a "mathematical" achievement, rather than a practical one. To check it on the ground every reading taken would have to be to a bipod or tripod - nobody does that.
Just for general interest, when we do tests on our aircraft after any repairs we will often include a check survey on the photography. Results from a couple of weeks ago, based on around 120 ground check points (gps on pole, three x 5 second readings at each location (locations selected at random whilst walking site, so the comparison with the air survey is onto the ground model and not an indicated and marked point):
Surface, mean cm, standard dev. cm.
stubble, -1.00, 5.68
track, -3.25, 3.28
new crop, 0.11, 1.83
rushes, -6.00, 5.29
bog grass, -5.00, 3.87
In P4D, if you process Step 1 first, then it makes identifying the targets in Ray Cloud extremely easy.?ÿ With PPK, the cross-hair is within a pixel or two before manually identifying the center.?ÿ So with a 12" target, it is extremely easy.?ÿ?ÿ
Here is a target with the GCP location estimated by P4D.?ÿ I have not manually selected the GCP center location yet.?ÿ This is typical results with the Wingtra.
Certainly the accuracy of the point cloud varies greatly with terrain type.?ÿ That is not what I'm trying to test in this project.?ÿ I'm mainly concerned with the best case scenario:?ÿ no vegetation, highly textured surface.?ÿ Primarily land development, where the vegetation has been stripped and they want a pre-construction topo.?ÿ Then progress and final topo.?ÿ In all of these scenarios, the terrain is only bare-earth.?ÿ There is a good market for this type of work.
Yes,for that type of work we expect 1-2cm. accuracy in height - plan accuracy for that type of work isn't so iimportant. Of course, since you will be putting down a model with huge numbers of points the overall accuracy will be far higher than a traditiional one done on foot -especially since the rod point would sink in to any soft areas (or the rod-man might not want to walk there!).
I've done extensive testing of flown topos.
In fact to stake out many of our reclamation sites the procedure would be to stake the work limits which were placed on actual generated points from the photogrammetry company, get a correction then lower or raise the control points and stake the site.?ÿ
Usually there was a "miss" high, normally about .5' we would raise the control .5' and proceed. These were optical photogrammetry sites with the flights covering large mapping areas.
Now that LIDAR is available our checks are more random and often quite good. One project was a 200 sq mile area that was going to have a railroad loop placed in it. We checked actual points near the loop and they fit randomly +/- .2'. Everyone was quite happy and I was pleasantly surprised.
For small drone flights with lots of ground control .15' seems to be about what it can do. Maybe a tad better.?ÿ
I figure surveyors always check photo control, just part of the job.?ÿ
Using RTK for check points, I always get 0.15' or better (usually <0.10') with 0 ground control with the Wingtra.?ÿ It's quite impressive.?ÿ This is why I want a more rigorously surveyed test grid to see how good it really is.?ÿ?ÿ
Wingra published a white paper claiming 1cm absolute horizontal accuracy with no GCPs.?ÿ But they surveyed the check points using RTK, so I'm not sure about that.
That is impressive and not what I've seen, the ground control targets we've set for drone surveys are always very extensive. Time consuming and dense. Mostly I could have driven a 4-wheeler around the site in less time than flying it and controlling it.?ÿ
I've also tested the Delair UX11.?ÿ While not quite as accurate as the Wingtra, it was still pretty good without GCPs.?ÿ It was within 0.2' vertically.
The new generation of PPK drones are quite impressive.?ÿ I wish they would add a high-precision IMU for areas that are difficult to calibrate (trees, water, etc.).
I think EVERYONE would like a good IMU to assist in the processing.?ÿ They are still pricey, and ITARS doesn't want anyone to have easy access to them for nefarious reasons too I suppose.
All depends on the site and if you can drive it. Some of the quarries it used to take me all day to walk can be done in less than an hours flight (repeat jobs have permanent ground boards in place). Typical board spacing we use is around 300 metres, or three across the width if that is less.
Last weeks job was 4.5km long, 0.4m wide - flying time around 3 hours. It took a day and a half on site just to add in the GPS check points the client wanted. This was a set of fields under crop (kale, broccoli, cabbage, cauliflower) so there was no vehicle access apart from a single track. Job is looking for ground settlement from previous utility works. Comparison with last year was very impressive; all the small twists and "jags" in last years contours (0.1m), which we thought might have been errors were replicated in this years results.
Whoops - meant 0.4KM!
