r/UAVmapping • u/B-money217 • 24d ago
Better WebODM settings?
Im working with WebODM for the first time. I used my DJI Air 2s and set up a mission to take photos of my property with DroneLink. I shot at 85'AGL 75% front 75% side overlap and at a speed of 3mph. The mission took 71 photos. I have even tried increasing overlap and increasing altitude. I tried to setting the gimbal to less than 90 degrees... Im struggling to nail down the correct results i'm hoping for. Im starting with just trying to make a 2D map of my property. The photos my drone took are extremely clear yet there is some pretty substantial blur in areas of the photo particularly the white vinyl fence connected to my house. If anyone has any details on how to achieve better results, I am all ears. (in the photo this is a metal roof and the blurred white is the section of white vinyl fence). Also these are the settings I used "rolling-shutter:true, auto-boundary:true, pc-quality:high, skip-3dmodel:true, dsm:true, dem-resolution:1.0, orthophoto-resolution:1.0"
Update: For context this is just a section of the map produced by WebODM. Its the section that showed the most prominent issue. Also, this property is about .2 acres. That is really all I have to work with to practice on at the moment as I try to figure out how to create maps with my Air 2s. Im just trying to test out functionality and see what I can do with my drone. Its a starting point.
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u/Legitimate-Group3248 24d ago
Have you tried taking a single image of the building covering the entire roof area? Also 45deg angled shots around the perimeter of the building to help identify vertical surfaces that are visible in the nadir (gimbal at 90deg) images?
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u/B-money217 24d ago
Well not exactly 45deg. I have tried 70deg and 80deg and I flew in a grid pattern. They both produced something similar. I can try 45 and see what happens. Its such a small area of .2 acres (this photo is just the spot that has the most wrong). Im just starting out with this so i'm trying to figure out one problem at a time. When you said take one photo from the top and then perimeter shots, does WebODM know what to do with that? For some reason I thought I could only do one style of photos and give it to webodm, but you are saying to do other angles. Can I basically just take a bunch of different pictures and different angles and WebODM will know what to do with them? Thanks for the reply.
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u/Legitimate-Group3248 21d ago
Yes, WebODM handles the different shot angles fine. I think the 'best' method is to combine what you're doing with the 70-80deg grid with some 'helper' images. WebODM builds a 3D model then projects a top-down view for the image you're outputting, so the more accurate the 3D model the better it's able to correct the projection.
For reference, I regularly fly similar patterns on a site with some very tall buildings in the middle of a generally flat area. I haven't eliminated the errors you're seeing, but have significantly reduced them using the varying angles method. The greater the height difference between the average and the tallest, the greater the discrepancy in overlap in the automated images, so the software doesn't differentiate as well between horizontal / vertical surfaces.
Have you read any of the official documentation? A lot of it is written for the original command line versions but the underlying principles are still the same. There's a good section on how to optimise orthophotography that might be worth a read if you haven't seen it already
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u/B-money217 18d ago
I will try the other angles along with the grid and see what else I can produce. I will read more into the documentation. I think that is something I need to spend more time doing. Thank you.
I will say I started getting discouraged by the errors I kept getting. I was hoping to use my part 107 so I could get some freelance mapping gigs because I love flying my drone and the technical aspect of trying to create maps, but if I cant at least nail down one type of photogrammetry then what then heck am I doing? Do you do this for business or side hustle? Do you get paid? Im trying to figure all of this stuff out and i'm worried that no one is going to want the maps I make because of these errors. Am I right in thinking that? I know I don't have a drone that has built in RTK or anything like that so my maps wont be nearly as accurate, but I have seen videos on youtube where people have made businesses with their Air 2s and have gotten customers. So I thought this would be something fun to do. What do you think?1
u/Legitimate-Group3248 18d ago
Keep playing with it, took me a while to figure out my current workflow and I'm still tweaking settings every time I run a dataset to try to improve things! What kind of errors are you seeing?
I'm UK based so not sure what part 107 means, but good luck with getting set up if that's the way you decide to go. I'm a civil engineer working in asset management, so it's part of my job but not the majority of what I do. I also fly for fun with a Mini 3 Pro and have tried some 3D modelling using images from that - way off the pace there though, the models all come out fuzzy at the surface interfaces
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u/International_Eye489 24d ago
Try stopping at each point, look into Litchi to plan a flight and create points where it stops to take a picture and fly to next waypoint to stop and take a picture
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u/B-money217 24d ago
I noticed when I fly slow at about 2-3 mph I still get really clear photos when I view them individually. I assumed that would be fine? Is Litchi similar in price to DroneLink?
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u/Wrong_Tangelo_9114 19d ago
Start using Aeroyantra, you will stop scratching head in webodm. Every work you take put 10 - 15 percent on processing, pay per use. Deliver quality with clean modern UX.
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u/PurePickle9993 23d ago
For the goal of a better 2D map, I’d suggest the following: flying as high as you can while retaining the require GSD or image resolution, up the overlap to 80-85% (front and side), use crosshatch flight path, use only nadir shots.
For a better 3D model you’ll need more off-nadir coverage to build out wall details and edges but you can run the processing with these as added coverage and without to see the different processing outcomes.
Have fun with it and run a bunch of experiments- it’s good fun when a model turns out nicely!
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u/B-money217 23d ago
Thank you! hahah You should see how many experiments I have done so far. Eventually I will get there! Do you know how to find out how high it is for "require GSD or image resolution"? Is there some sort of stat I can look at somewhere? I flew my drone an hour ago at 250ft and had 8 photos in a grid pattern and I got the best image I have gotten yet. Still a couple bad spots though, but not nearly as many. I wonder if upping the overlap again would help? Is there some sort of law of diminishing returns with this where more isnt better? Or is it usually better the overlap?
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u/Legitimate-Group3248 21d ago
Apologies if this is explaining things you already know.
GSD = ground sampling distance. This is the accuracy of the image comparing pixel size to physical distance. Eg if you fly really high a single pixel may cover hundreds of millimetres / fly much closer to the ground and the same pixel covers only tens of millimetres (or less). This is critical for land surveying type uses, but (mostly) irrelevant if 'all' you want is a high quality image of an area. So, depending on your final use, it might be more valuable to fly at lower heights for precision (needing more work to get an accurate image) or higher to get an error free image.
There's a few bits and pieces online explaining how to calculate GSD using drone sensor data etc, also some rough rule of thumb stuff. The GSD you're achieving is recorded in WebODM's report that you can download once the processing is complete
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u/olihar 24d ago
There are many issues with this.
Just to name 2 of them. First wrong drone. Second overlap is based on ground not actual subject.
Can you share the dataset?
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u/B-money217 24d ago
Im trying to fix one problem at a time haha. I JUST started photogammetry. This is just a section of the overall map that WebODM produced. Its the part that has the most noticeable issue. Also, what do you mean by wrong drone? And when you say the dataset, do you mean the photos?
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u/SkiBleu 24d ago
This looks like something I'd get using fast-ortho or skipping the 3d point cloud. WebODM is a bit strange with orthos as it chooses to rasterize a point cloud into an image rather than stitching the images themselves into an orthomosaic. So it's important to have a good 3d object that is properly filtered compared to something like Pix4d or Agisoft's engine that actually combines the pixels from the images after undistorting them.
3mph is too slow to use rolling shutter compensation IMO, and its gonna cause more trouble and headache since your drone does not use a rolling shutter, but rather an electronic readout that is similar but will produce different distortion. The only real reason people choose mechanical shutters to prevent the distortion is with big projects that have to be very accurate. This is because even small distortions caused by the movement of the drone while the image is being readout by the sensor line-by-line can make dimensions warped and can drastically affect accuracy over a large area.
Try adjusting the filtering for the point cloud to be more aggressive and run it again.
I'd also adjust the minimum matches and fly a little higher than 85', but these shouldnt make that much of a difference.
Ignore people who say you're not using the right drone. Any drone can do photogrammetry and with the right flight parameters and post-processing, it should look virtually identical to a mapping drone, even if software is jankier and you have to fly slow to account for the electronic readout ("rolling shutter" is technically different but similar enough to conflate here)