Sweet spot settings for DJI Air 2s in combination with WebODM.
Hi all.
I've been testing quit a lot but still haven't found the sweet spot settings in Web ODM to create a decent resolution image.Is there anyone who has an overview of the WebODM settings that produce good quality images?
I use the local WebODM on a MacBook Pro 2021 with a M1 chip and 16GB of RAM but lots of times it's seems not enough. Therefore I've tried some settings with resizing the images to give my MB some air but I am still not satisfied.
The Dronelink settings are mostly: Hight: 90 meters - Overlap: 75/75 - Speed: 22km/h - GSD 2.54 (matching my drone sensor size). With the hight set to 60 meters the GSD improves to 1.7 but produces a lot more images.
Anyone who has some good settings for the combination of Dronelink and WebODM?
Best Regards,
Danny
Comments
7 comments
Some suggestions, and there are others here that use WebODM that may chime in.
1. Slow down, unless you have a lot of ground to map, the slower the better, within reason. (I usually fly between 4-8 MPH) Cameras have rolling shutters, not mechanical so are subject to more distortion from speed. Look around Barry just did a study on this. Commercial people with great drone/camera combinations fly quite fast especially with a mechanical shutter. (sigh.... I have more time then money so just fly slow)
3. To increase resolution GSD, I think you have to go lower, at least that is what I find with my Mini2. You have a better camera though. At 80' I can get under .8 cm/pixel according to WebODM numbers. I just did a map at 100' and it is 1.07 cm. When you think of the Mini2 small camera and sensor, I think that is pretty remarkable!
4. In WebODM read the forums, there are lots of suggestions for improving your orthophoto/orthomosaic.
5. There is also an offset in the WebODM settings for rolling shutter, you can turn that on and use 25-26 for the number. Sorry, this is probably not correct, it must be calculated for your drone/camera. Check their list of known offsets. Again, there is a page on their web site to explain this.
6. I can't really compare systems, but some of my orthophotos take a couple hours to process, the same map on a different day (lighting? a little windier?) may take 16 hours. I have one running right now, 152 photos, at 13 hours, and nearing completion! The "Fast Orthophoto" setting gives decent results, but I think it can be improved on.
My current settings: auto-boundary: true, dem-resolution: 2, dsm: true, fast-orthophoto: true, mesh-size: 300000, orthophoto-resolution: 2, pc-quality: high, rolling-shutter: true, rolling-shutter-readout: 25
Danny
Like you, I am using Macs these days and, while they are great for video editing, they lack the RAM needed by WebODM. I have an M1 Macbook and an M2 mini with 16GB. The Mini is good up to a point and then just fails.
There is an alternative where you can offload the processing to a thing called WebODM Lightning - ironically I have a 5 Minute Friday that will either go out tomorrow or next Friday, but if you need it I will make it tomorrow's one. That way you can process smaller maps locally and larger ones offline, and the workflow is almost identical.
You don't say what you are producing with WebODM. In general (if I recall correctly) they recommend 75% overlap for ortho and 83% overlap for 3D rendering.
As George mentioned, the Air 2S can be prone to blur since it doesn't have a mechanical shutter so you can solve that by slowing the capture speed down (2 videos out on that one).
Hi George and thanks for your information.
I am going to try out the new height-settings in Dronelink together with your WebODM settings. Unfortunately the capture speed in Dronelink can only be changed in the Expert Growth plan with a monthly fee. I'll have to play with the rolling shutter offset settings then. For the ones interested: For the Air 2S it's 32ms
P.S. My GSD is 0.85 cm/px on a hight of 30 meters.
Danny, You are correct in saying the *capture speed* cannot be changed on basic plans. (Unless I am corrected, since I only have one old plan, I don't know what all the others do.) However the speed the drone is flying can be changed under the "Speed (max) setting (1). This will automatically change the capture speed (2). This is because it is a calculated value based on overlaps, height, camera FOV, speed of drone, etc. Changing it manually would mess with the overlaps and probably make you unhappy with the results, so you have to work with what you can change.
Hi George and Barry,
I forgot to mention the flight speed as an option in Dronelink. I lowered that one from 28/32 to 12 km/h so that should bring some improvements combined with a lower altitude.
@Barry: I use WebODM primarily for Ortho photos and I know the option for Lighting. Maybe I can switch to that when I really start making money with this.
P.S. A little while ago I read an article about a guy from Norway. That guy produced a overview of the shutter speeds combined with the flight speed to prevent motion blur. That's something important too and a interesting read.
https://www.ntnu.no/blogger/richard-hann/2021/10/07/preventing-motion-blur-in-drone-mapping/
Thanks so far.
Regards,
Danny
Good information.
Higher shutter speeds certainly make a big difference. My issue is that I'm lazy LOL. Often I am taking photos and videos in the same location and, with the Air 2S, it is easy to blow out the highlights if not using an ND filter on bright days. I'm also often trying to make video more interesting by aiming to get the "180 degree rule", which often entails using ND filters.
If I have an ND on then there is a decision to make before mapping. Do I land and remove the ND, since it's rarely too bright facing straight down, or do it just capture at a slower speed.
This is less of an issue with other drones that have an adjustable aperture or (even better) a mechanical shutter.
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