Difference Between Types of Image Overlap.
Hello, all.
I generate orthophotos using WebODM. On their tutorials page, they mention a specific pattern to be flown to mitigate errors and maximize quality in orthos as well as one of the routes being flown 5° off nadir. The wording they use and the wording on the dronelink mission planning page differ, and I was wondering if anyone could help me figure out what to do.
WebODM states, "To get good 2D and 2.5D (digital elevation model) results, you will require 42% overlap and sidelap for an equivalent 70% overlap and sidelap."
Does this mean I should set both my Front Overlap and Side Overlap to 42%?
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I have read that same article several times. I believe they are basically saying at least 70% overlap for each works out to a final of 42%. (???) I can say that I usually set mine to 80 front, and 75 sidelap. I think using only 42% would not give good matches, especially if you have some "tougher" terrain. (Trees, water, sand dunes? etc.) As an aside here, trees, forests, don't do well with the slightest wind, at least for me. There is maybe to much movement in the upper branches that WebODM can't match images.
The 5° is not overlap, but off nadir, or -90°, so you can set to -85° if you desire. (Other articles show up to -75°) This helps with 3D to capture sides of items such as walls, or sides of trees, etc. You can also fly the 2nd path itself at a diagonal from the first path. Either the DL "built in" 90°, or more like 30° they show on WebODM.
There are some other knowledgeable WebODM users here that can confirm or set us both straight!
George K I also don't know what they mean by the 42%, lol.
Personally, I haven't noticed wind affecting anything in the orthos aside from the actual look of the trees in the final ortho, unless that's what you mean. I ran a mission last week in 35+ mph winds and only two or three photos were wonky, assumedly because of my rolling shutter.
I also use the -85° gimbal angle all the time, but only on one of my two routes. As they mention, I fly 2 routes 20° off one another and only on the second route do I implement the non-nadir gimbal. I think that's what they mean (???) and it's given me some incredibly impressive results for the equipment I'm working with.
Hopefully an ODM genius appears soon :)
I tend to fly 80% front and side overlap, one run with nadir at 285 feet, then drop to 185 feet with -65° gimbal angle for a second run
For me if it is 80/75° for a ortho 2 grids my Altitude between 60 and 90 meter ..depending of the location and the size. Camera angle -90 . For 3d I go 85/85 and do 5 grids 4 oblique 1 nadir height also depending of the location. That remark about 42% I have also no idea
Martin Reading I was wondering about this method, too. Do you find that the ortho quality is better in areas that the oblique and nadir runs overlapped? My concern, after taking battery life into account, is that the areas than have oblique AND nadir images will end up being noticeably higher quality than those without 2 views. Maybe I'm overthinking.
James Alexander Swentzel, check this out, taken with mini2 https://maphub.online/430-342708-044
That little mini 2 is something else.mini 2 still got fight in it.still worth to buy for a beginner that doesn't want to spend much.
Victor, I reckon its possibly the best bang for the buck out there, and no real restrictions on where you can fly it here in the UK
Yeap,here in America I got the Air 2s collecting dust I'm scare to fly.you get a ticket quick I'm losing interest in this hobby to many rules
Victor What do you mean? I also have an Air 2s that I use on a daily basis, recreationally and commercially.
Yeah even recreational here in New Jersey cops mess around a lot.
Victor You must be unlucky; I've had nothing but pleasant encounters with law enforcement (in terms of drones).
Most officials I interact with are actually very curious about drones and [kind of] look to me for help being informed about them.
I am curious her in the EU (belgium) we have 4 categories A1 A2 A3 and specific according to the European drone legislation the A1 category is normal for max 250 grams and you and are permitted to do a lot ,in a2 you need to take a extra exam that is for the max 900 grams and you have more restrictions ...now my dji mavic 3 has a C1 label that means I can fly with it in open A1 ..is that also in the US or UK?
And when I fly with my m3 in a city the police comes and scratches their head because the can't understand why a 900 gr drone is permitted in de lowest category
@georges In the U.S., we have Category 1, Category 2, Category 3, and Category 4 Unmanned Aerial Vehicles.
Category 1: drones under 0.55lbs (0.25kg).
Category 2/3: greater than 0.55lbs but incapable of causing injury to a human greater than that equal to 11ft/lbs of kinetic energy and the operator does not have a certificate under Part 21.
(I am not sure of the difference between these categories.)
Category 4: UAVs used and registered outside of the U.S.
I've had drone-related interactions with law enforcement 4 times thus far, all of which were because someone called thinking I was spying on them (guilty conscience). Surprisingly, none of the officials I've spoken to actually knew anything AT ALL about drones or the laws surrounding them.
Thx for the answer!
@George K So I spoke with some guys from the WebODM dev team. Apparently, 65% front overlap and 65% side overlap results in an overall overlap of 42%, since 0.65 is the square root of 0.42.
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