Thank you Lukas! This is extremely helpful.

I agree that it is not a simple example. I'm getting this: 
http://78.46.190.157:8080/birds.jpg, ie, good alignment but the mapping 
is a little wonky. While I don't think my result is great I have some 
thoughts about that: 


This is better than anything I've managed so far, this looks really good! 
Thanks for trying!
 

-- the images overlap far too much. I have removed 2 out of every 3. 
That could be done systematically, if they always overlap that much. 
One could also truncate each image. 


Okay, that's good to have confirmed. I suspected something like this might 
be happening, and at one point I tried stitching "adjacent" images (based 
on EXIF timestamp) into mini-panoramas before stitching the bigger one, 
which seemed to help somewhat. I can repurpose that logic to simply skip 
images taken close together instead.
 

-- I assume the images have been shot out the side of the plane, ie, not 
vertically down. Then it is not correct to set yaw and pitch of the 
anchor to zero. (I'm getting a yaw of ~20degrees). 


Yes, this is correct. And thank you! I don't think I would have ever 
realized this about the anchor on my own.
 


-- freely optimising y/p/r/Tx/Ty/Tz of many images hardly ever converges 
into the intended minimum. The obvious strategies are to optimise a few 
images, add a few more, optimise them together, etc. Here, I have 
optimised first Tx/Ty for all, then y/p/r for all except the anchor, 
then y/p for the anchor. Tz has only been included for some images -- 
optimising it for all yields better agreement but a worse mapping (and I 
assume the plane has been at a consistent height). I don't have a good 
idea how to deal with that -- the problem is obviously that the degrees 
of freedom are not orthogonal. 


Okay, perfect, this sounds workable. I hadn't considered a multi-pass 
optimization like this, but it makes sense to do positions and y/p/r 
separately to prevent them from confounding each other during optimization. 
I think that the plane GPS track may be available somewhere in the data 
dump, so it might be possible to impute an elevation to the images based on 
timestamps. It probably wouldn't be precise enough to use directly, but 
perhaps it could be used as a starting point that is close to reality. But 
that sounds like an idea for v2. :)
 

-- having any right angles on the ground and using them for line control 
points would help very much. 


This is good to know. There aren't always going to be straight lines 
available but in some cases there may be due to debris. I will keep an eye 
out for opportunities to use this.

Thank you very much for your help!

Best,
Derek
 


best regards, lukas wirz 



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