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I've never used photosynth. Here is an example of a series of 360 panoramas I've made in a tunnel http://www.360cities.net/tour-preview/crrel-permafrost-tunnel-panoramic-tour . What I'd like to know is whether I could photosynth to create a seamless version of these individual panoramas. Ideally what I'd like is to create a true 3D model, extract a point cloud, create a tubular surface from it, and then texture the surface with the photos as a seamless mosaic that one could move through. Is something like possible in photosynth? I'd appreciate links to anything similar or related.
From just a cursory look at your panoramas, I'm tempted to say that they are probably spaced too far apart to make strong links between the positions and because of this, you probably won't get a good point cloud to construct a mesh from and subsequently texture. The exception to this might be where the two tunnels meet because the density of the coverage doubles as the two lines of positions converge and that space is much more open, meaning more content in common between photos.
That said, you shouldn't take my warning as the final word. Rather, try the source photos in Photosynth at your leisure (there have been publishing problems in the last several days, but the Photosynth team reports that those are fixed now) as it is completely free and see for yourself how they perform, simply keeping in mind that the positions that the photos were taken from may be too far apart for Photosynth's matching algorithms.
If you do find that part of the reconstruction is good, I would make a synth with only the photos of that part of the tunnel and then use Christoph Hausner's SynthExport, Kean Walmsley's BrowsePhotosynth AutoCAD 2011 plugin (if you're an AutoCAD 2011 user), or Henri Astre's PhotosynthToolkit to extract the Photosynth point cloud to then open in Meshlab or other modeling programs.
One thing which Henri's PhotosynthToolkit will give you is that it is designed to convert the Photosynth coordinate system into a format which Yasutaka Furukawa's PMVS2 dense point cloud generator can use. PMVS2 was actually originally designed to work with Noah Snavely's 'Bundler' program, which is the continuation of the code which he used in his 'Photo Tourism' project which inspired Photosynth, but Henri figured out how to plug Photosynth reconstructions into it. Given a good sparse reconstruction from Bundler or Photosynth, PMVS2 will do very well.
I should probably add that as you get into dense reconstruction with PMVS or other tools, you should anticipate needing a considerable amount of RAM (and consequently a 64-bit operating system).
Other avenues of research for you:
Autodesk Photofly: http://labs.autodesk.com/technologies/photofly/
(Provides a similar reconstruction process to Photosynth, but offers their Photo Scene Editor program to manually reposition errant or unconnected portions of the reconstruction)
Agisoft PhotoScan: http://www.agisoft.ru/products/photoscan/
Again, you'll need some RAM to use this with many photos, but it's definitely worth a look.
For dense reconstruction, using Bundler will allow you to break the dense reconstruction into smaller pieces via Yasutaka Furukawa's CMVS.
Bundler for Linux: http://phototour.cs.washington.edu/bundler/
Bundler for Windows: http://francemapping.free.fr/Portfolio/Prog3D/BUNDLER.html
Greg Downing/xRez Studio
Links to previously mentioned resources:
P.S. Now that I think of it, a better link for Bundler would be:
Josh Harle's Bundler Photogrammetry Package: http://blog.neonascent.net/archives/bundler-photogrammetry-package
Henri Astre's Structure from Motion Toolkit: http://www.visual-experiments.com/demos/sfmtoolkit
Both include Bundler, CMVS, PMVS2 and other utilities to get things working with custom scripts to make using the tools as simple as possible.
Anyway... all of this may be more than your question really warranted, but I thought that you would be one who could take the resources and run with the research on your end.
Ultimately, I'd say, just dump the photos in Photosynth and see how things go. Hope to see your results soon. Feel free to put a link to your synth here when you've tried it and ask questions. Someone will be happy to get back to you.