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Re: Please try to merge these files for me using hugin

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  • John Houghton
    ... With rectilinear projection, all straight line features are preserved so it is possible to use horizontal line points on the long horizontal architectural
    Message 1 of 5 , May 5, 2009
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      --- In PanoToolsNG@yahoogroups.com, Leonard Evens <len@...> wrote:
      > But after I changed your image to rectangular, the image
      > had the same problem mine had, namely it still needed some further
      > horizontal perspective correction. ... It should be possible to get
      > hugin to do that automatically, but I still can't figure out how.

      With rectilinear projection, all straight line features are preserved so it is possible to use horizontal line points on the long horizontal architectural lines in the upper half of the building. It is then necessary to optimize y,p,r of both images in order to allow the image to shift sideways into a position where the horizontal features are both horizontal and parallel.

      > 2 Changed lens type of 2nd image to be lens 0
      >
      > I assume you mean you changed the lens number so that both were 0.
      > What was the purpose?

      Both images were shot with the same lens, so they share the same lens parameters, i.e. the ones associated with lens 0.

      > Is there any advantage, except time saved to generating points
      > automatically?

      No. Provided the points are accurately placed and well spread out, the method of generation is irrelevant.

      > 6. Optimize y,p,r b + y,p,r of image 1
      >
      > Was there some rationale for this choice?

      This is just one of the options on the pull down menu. I don't use Hugin myself as I prefer PTGui, and in that I would set parameters manually: b + y,p,r of image 1. That can be done in Hugin with custom parameters. It doesn't really matter, as the image is going to be centered and levelled later. Either way, the optimization does a basic alignment with correction of barrel distortion (via parameter b). (Actually, I think I had second thoughts and set the parameters as I would for PTGui, after seeing Hugin set y,p,r for both images automatically).
      >
      > 7. Centre on preview window.
      > 8. Custom optimization as above but with a and d and e also included.

      This refines the correction of lens distortions (a & b) and corrects for the image offsets due to the lens shift (d & e).
      >
      > 9. Added 4 vertical line points (2 on each image)
      >
      > Why not also horizontal lines?

      See above. My project specified equirectangular output. Horizontals are not preserved in that projection so horizontal line points aren't appropriate (horizontal lines are not rendered straight).

      > 10. Custom optimize as above but now include p & r of image 0.

      Evidently, as noted above, at some previous point I anchored image 0 by unchecking y,p,r of image 0. When levelling with vertical line points, you need to check y,p,r on all images, except uncheck yaw on any one image to prevent the whole panorama image sliding sideways (unless you also have horizontal line points and need to allow the panorama to shift sideways).

      > 11. Average distance is now 1.1 but max is 4.
      > 12. Optimize with fov and lens param c included.

      Optimizing fov sometimes unfortunately results in fov ending up as 0 (since the control points are then all at the same point and the cp distances are a minimum - i.e. zero). However, often the fov will be optimized to its true value so it's worth trying. Here it worked. Parameter c isn't usually needed, but some lenses have peculiar distortion that c can help to correct. Again, it was worth trying to see if an improvement could be obtained.
      >
      > 13. Centre the image
      > 14 Stitch the output..

      John
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