Using WebODM to Process Drone Imagery (RTK or GCP) & Perform an Accuracy Assessment with QGis Part 2

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Күн бұрын

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@thomastucker301 8 күн бұрын

Virtual Surveyor is a great software that will actually do the RMSE calculations for you. It's not that expensive compared to most drone processing software, $2250 yearly. You can drag your dsm in it the drag csv of Topo points and export a check report that's gives RMSE. It's wonderful. Thank you for your video! It helped with WebODM a lot. Qgis was interesting too. I hadn't heard if it, not sir will use it nit great to know if more tools.

@SKYLINEFILMSBRASIL 4 ай бұрын

Great class! It is not only a tutorial.

@endurbia Жыл бұрын

Thanks for the video. What do you mean by ‘topo points’? Are those just checkpoints that you surveyed site?

@nathangeomatics Жыл бұрын

Yes, the topo points are the elevations I collected with the rover GPS rather than the drone. I use them as my second set of data so that I can have a comparison with the drone data.

@jacksonmacd 2 ай бұрын

Thanks. I had the same confusion and question. Glad you cleared it up.

@Project314 2 жыл бұрын

Good job on the tutorial! Can you explain why you need to correct the DEM with this method in QGIS if WebODM has you incorporating GCP's that are made with RTK GPS? Is this because WebODM GCP matching tool is really for matching a lat/long location and not so much the elevation?

@nathangeomatics 2 жыл бұрын

In the example I used direct georeferencing to assign all x,y,z values. I simply showed the steps on how to use GCPs but I never actually ended up using them for georeferencing. The GCPs used in this portion of the tutorial were used to check for a bias and not georeferencing and thus weren't technically GCPs at all. I continued to call them GCPs simply because it allowed me to spilt my data into two data sets nicely without becoming too confusing. I needed one set of data for the bias correction and the other for the accuracy assessment. If you used GCPs for georeferencing you wouldn't need a bias correction because the values of the GCPs were used to assign the values to the imagery.

@Project314 2 жыл бұрын

@@nathangeomatics thanks for the clarification. On a side note I've come to the belief that putting out dedicated targets in the field is of limited wisdom as it's often possible to use natural landmarks (manmade painted lines for parking or traffic control or cast concrete features for surveying), albeit it's probably a bit unorthodox. Which means that I can collect RTK GPS data after the fact and back-fit it into the ortho's. I guess the point I can glean from your tutorial is that I can use WebODM for generating a georeferenced DEM with low quality and conventional GPS data, and then I can do my adjustments with the RTK datapoints in QGIS instead of feeding them into WebODM. Does that make sense? (For a point of reference, I am new to this as a mechanical engineer and not a surveyor by education/trade/credential).

@Project314 2 жыл бұрын

@@nathangeomatics can you also tell me about GCP limitations on 3D models generated in WebODM? I've been flying sites low and higher gimbal angle (say 125 feet and -55 below horizontal, plus at -80 for the ortho) hoping to improve upon my point clouds and 3d textured presentation. That being said, does it make sense to feed RTK GCP's in to help correct the overall geometric integrity, or does mapping the GCP points in to WebODM pictures taken at odd angles result in iffy results? Or does this really help a lot with elevation correction?

@nathangeomatics 2 жыл бұрын

@@Project314 It is for sure possible to use existing features as GCPs and they would be just as valid but that could lead to confusion. For instance, using paint lines in a parking lot; its possible you might measure the wrong line intersection. Additionally, clear features aren't necessarily always available, for instance the survey could be in a pasture or field where there aren't any easily discernable features. Using a target will ensure you will always be able to get the exact center and it will be high contrast. You don't need targets but it will ensure consistency in your GCPs and will likely make the processing easier. You're also supposed to have an even distribution of GCPs across the whole study area and placing your own GCPs will guarentee that rather just relying on chance that you'll have enough evenly distributed distinct features. In short, you don't need to place targets but you probably should.

@nathangeomatics 2 жыл бұрын

@@Project314 You don't need GCPs at all if your drone is equipped with a high precision GPS. I used them to help with an accuracy assessment. I didn't try two different angles being processed at the same time in WebODM, in order to get better coverage I flew a grid pattern so that photos were taken perpendicular to each other but the angle remained fixed. according to Meinen et al. (2020) a combination of nadir imagery and oblique 15-degree imagery is best but will have very similar accuracy to nadir imagery with a dense distribution of GCPs. James et al. (2020) however suggests 10 degree inclination because 15 degree may result in “promoting a previously unconsidered correlation between decentring camera lens distortion parameters and the radial terms known to be responsible for systematic topographic error”. I'm not totally sure how WebODM will handle two different angles and GCPs but you should try it. As long as your target is fully visible the angle shouldn't be a problem. If you're going through the effort to use GCPs anyway you could always head into QGis after the fact and preform a bias correction if deemed necessary. Meinen, B. U., & Robinson, D. T. (2020). Mapping erosion and deposition in an agricultural landscape: Optimization of UAV image acquisition schemes for SfM-MVS. Remote Sensing of Environment, 239, 111666. doi.org/10.1016/j.rse.2020.111666 James, M. R., Antoniazza, G., Robson, S., & Lane, S. N. (2020). Mitigating systematic error in topographic models for geomorphic change detection: Accuracy, precision and considerations beyond off‐nadir imagery. Earth Surface Processes and Landforms, 45(10), 2251-2271. doi.org/10.1002/esp.4878

@danpeters3903 2 жыл бұрын

what kind of device did you use to assign the long and laditude to the GPCs?

@nathangeomatics 2 жыл бұрын

I used an RTK GPS unit in conjunction with a base station. You can use pretty much whatever you want to assign x,y and z values to your GCPs such as a total station or a network connected RTK GPS (Cansel for example), the technology used will have an effect on the accuracy of the entire survey.

@danpeters3903 2 жыл бұрын

@@nathangeomatics Can I use a handheld GPS device to do the same. I am trying cut cost.

@nathangeomatics 2 жыл бұрын

@@danpeters3903 You could try to use a handheld device but practically speaking that has an accuracy of +-3m. That means that your survey will have at the very best 3m accuracy. I would not recommend using a hand held device. If you absolutely need to use a handheld device take multiple measurements at each GCP and average those measurements in order to hopefully get something closer to the true value. For GCPs with the GPS I used it automatically took 180 measurements and averaged the shots. Doing 180 shots manually is of course not practical and probably not even useful with a handheld device so just take as many as you have time to do, I wouldn't go crazy maybe like 10 measurements in order to get a little closer. You should also do your best to place the phase center of the GPS antenna directly over the center of the GCP might not make a huge difference but might as well try. All that being said you likely won't get a very accurate survey but if all you need is +- 3m you should go for it! Let me know how it goes!

@johnrogers3315 2 жыл бұрын

@@nathangeomatics many thanks for the tutorials, they're really helpful. Would appreciate your views on whether the on-board GPS on a mid-range DJI would be able to capture

@nathangeomatics 2 жыл бұрын

@@johnrogers3315 a stationary shot for 10min will yield much better results than capturing locations while its flying. Without RTK it will have limited accuracy but you should always do your best to make the most out of what you have available. Without RTK your absolute accuracy might not be great but the relative accuracy still could end up being quite good. Depending on your region there may be published data available for vertical control monuments and you may be able to place the DJI over a few different ones to get measurements allowing you to make a vertical correction to your vertical data if deemed necessary. I haven't tried using a hand held GPS or the onboard GPS on a DJI to do a survey but that is for sure something I want to try out next time I have a drone available. If you try it out let me know how it goes I'm quite interested to see the results.

@steevolicious 3 ай бұрын

What’s the benefit of using exit tool?

@nathangeomatics 3 ай бұрын

@steevolicious so the exif tool is simply the way I used to view and update the data associated with each image. What I liked is that it could do a mass update on all the files quickly and easily.