I'm trying to assemble a specific vertical panorama, but also trying to 
learn methods for assembling a vertical panorama.

One major issue (that I'm furthest from figuring out on my own) is the 
exposure issue:
Taken on a cell phone (fixed F 1.9, Focal length 2.91, aperture 1.85, not 
sure those even have the same meaning as on big camera) with auto varying 
time:

Bottom photo is 0.025 sec exposing the street well and including some 
totally blown out sky.
Middle photo is 0.0083 sec exposing buildings well with sky blown out and 
street too dark.
Top photo is 0.0073 sec exposing the sky well.

I definitely don't want to compress the range.  I'd rather be dishonest 
than correct for that.

If the alignment were perfect, then doing no exposure correction would work 
with the blending from one image to the next smoothing the exposure 
transition.  But I haven't gotten the alignment near that good and would 
like to learn how to live with poor alignment.  That involves narrower 
transition zones in controlled places, which would then generate ugly 
exposure jumps.

What I think I want is a height based exposure shift in each photo (rather 
than the usual exposure to exposure nonlinear mapping to compress the range 
without losing much detail).  In each photo I think I want a smooth 
transition from making the bottom a little brighter to making the top a 
little darker.  Then the same final pitch of each photo would match in 
brightness.

I think this height based exposure issue may be a common problem, not just 
something in this set of three.

1) Have I misunderstood the issue and there is a very different basic 
solution?

2) Or is there a way already in hugin to adjust exposure the way I 
described?

3) If I need to use an external tool, how should I measure the amount I 
want to adjust exposure and/or compute it from the exposure times reported 
in EXIF?

4) What open source tool is easiest to use to pre-apply an exposure shift 
based on vertical position.

Also, is there good info on the other techniques for a narrow vertical 
panorama?  I don't know what projection works OK.  The best I found with a 
google search is to turn the whole thing sideways and use the usual methods 
for that kind of panorama, then rotate it afterward.  Is that really the 
best way to do narrow vertical?

I can put the photos and project etc. on my google drive and provide a 
link, if that would really help.  But I would prefer generic advice that 
fit this category of problem rather than specific help for this set of 3 
images.

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