[ptx] suggestions for stitching aerial photos

[Rik Littlefield]

Rob Park wrote to me offline:

>When I was stitching the photos, it
>
>seemed like it was not even really necessary to correct the images at
>all, only to position them for stitching (eg, they need to be moved
>around relative to each other on a flat plane, but don't really need
>much in the way of lens correction). Setting the lens to 2 degrees
>seemed to have the best effect, but is there a way to tell hugin to
>operate in a flat plane instead of the 360 degree universe that it
>expects?
>  
>
>  
>
I am replying on-list because I think the question is of general 
interest.  It also exposes some difficulties with the hugin gui.

One way to do the stitching that Rob wants is to set a=b=c=0, do NOT 
optimize pitch/yaw, but DO optimize roll/d/e individually for every 
image except the anchor.

This may seem bizarre, but if I have done the math right, it exactly 
models what you want.  Varying roll/d/e corresponds to 2-dimensional 
rotation and shifting when the input and output images are rectilinear 
and there is no a/b/c correction.

In PTGui, this strategy is easy to implement -- just check the 
appropriate boxes in the optimizer panel.  A bug in the PTGui editor 
window prevents me from seeing the entire result.  I have to actually 
stitch to see it.

In hugin, I cannot figure out how to do the optimization just with the 
gui (windows version "0.4 pre" dated 9/15/2004). 

I can get the optimization to work by manually editing the optimizer 
script, for example to insert the line

   v d0 d1 d3 d4 e0 e1 e3 e4

After optimization, the hugin preview still looks awful -- apparently 
huge stitching errors despite good results reported by the optimizer.  
But the final stitch through nona is fine.  Perhaps there is a bug in 
hugin preview also.

But I do not have much experience with hugin.

Perhaps someone can tell us how to do the roll/d/e optimization more 
easily with the hugin gui.

--Rik

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