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Re: cubicQTVR projection

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  • Hannes Hensel
    ... Hey Rik, thanks so far. That goes into the right direction. I m only trying to get a bit deaper in that graphic stuff, to understand what is done there.
    Message 1 of 13 , Dec 30, 2006
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      > Can I ask, why are you looking for these formulas?
      >
      > --Rik

      Hey Rik, thanks so far. That goes into the right direction. I'm only
      trying to get a bit deaper in that graphic stuff, to understand what is
      done there. And I wonder, if there is a shortcut, to do those 2 steps
      in one (sph > cube and cube > viewer = sph > viewer). Than it should be
      a sphere with the vCamera (central point) as center and the viewing
      plane inbetween (inner surface of the sphere BEHIND the viewing plane),
      right? How is the zoom realized then? Is it only done by bringing the
      viewing plane more to the camera (zoom out) or more to the sphere (zoom
      in)?
    • Rik Littlefield
      ... Hannes, Yes, zooming is equivalent to changing the distance between projection plane and center of projection. All of these operations can be combined into
      Message 2 of 13 , Dec 30, 2006
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        --- In PanoToolsNG@yahoogroups.com, "Hannes Hensel" <h.hensel@...>
        wrote:
        > How is the zoom realized then? Is it only done
        > by bringing the viewing plane more to the camera
        > (zoom out) or more to the sphere (zoom in)?

        Hannes,

        Yes, zooming is equivalent to changing the distance between
        projection plane and center of projection.

        All of these operations can be combined into one step, for some
        definition of "step". They are usually kept separated to simplify
        thinking/coding and to move the cost of computations to where they
        can be afforded.

        A little more discussion...

        In my previous reply, I followed your lead and wrote in terms of
        lat/lon --> cubic image coordinates --> viewscreen coordinates.

        But in fact, the transformations are usually run in the opposite
        direction. For each viewscreen pixel, one computes the corresponding
        cubic image coordinates. From cubic image coordinates, one computes
        the corresponding lat/lon. From lat/lon, one computes the
        corresponding coordinates within a "perfected" camera image (after
        correction for lens distortion). From those, one computes
        coordinates within the camera image -- the one that was fed to
        Panorama Tools as a source image.

        Pixel value interpolation typically occurs at several places in the
        pipeline, once for every actual image that is constructed. Suppose,
        for example, that you run Panorama Tools to stitch multiple camera
        images into a single equirectangular image, then run PanoCUBE to
        generate a cubic file, then view with QuickTime or ptviewer. In this
        case there will be at least three separate interpolations of pixel
        value: one to go from camera images to equirectangular image, a
        second to go from equirectangular image to cubic image, and a third
        to go from cubic image to screen image.

        In theory, all of this manipulation could be combined into a single
        step, generating a screen image directly from camera images with only
        a single interpolation of pixel values.

        However, that would put the entire cost of the calculation into the
        viewing loop. At present, that's not feasible because it would be
        too slow. Instead, the expensive calculations are done once, to go
        from camera images to cubic image file, so that only very simple
        calculations are needed for interactive panning/zooming. The viewing
        calculations can be done quickly even in software, and are simple
        enough to be done in hardware for even better performance.

        It is interesting to notice that if you start with camera images from
        a perfect rectilinear lens, then in theory the entire viewing
        pipeline can be done without any spherical trig at all! All this
        lat/lon stuff is just a convenient way to think about the
        calculation. Ultimately, what's being accomplished is only to
        project each planar camera image onto the planar viewscreen. That
        process requires only matrix multiply and perspective division, using
        homogeneous coordinates. I'm not aware of any software that actually
        takes this approach, however.

        --Rik
      • Hannes Hensel
        ... Yes, that s true, but there is the problem of blendig, then. If the images were perfect, that should be no problem. But if they did not fit 100% or have
        Message 3 of 13 , Dec 31, 2006
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          --- In PanoToolsNG@yahoogroups.com, "Rik Littlefield"
          <rj.littlefield@...> wrote:

          > It is interesting to notice that if you start with camera images from
          > a perfect rectilinear lens, then in theory the entire viewing
          > pipeline can be done without any spherical trig at all!

          Yes, that's true, but there is the problem of blendig, then. If the
          images were perfect, that should be no problem. But if they did not fit
          100% or have some exposure differences, one would notice that in the
          viewer. Maybe it would be a good approach, to correct and blend the
          images, but to leave their ratio and size. Still it would need some
          more calculations, like z-buffering, but that shouldn't be a problem.
          The question here is: is there an advantage in having the (almost)
          original images available in the viewer or its context? I can already
          hear "Protect my images! Copyright!" - which is an important thing...
        • Hans Nyberg
          ... The fact is there is a guy who stitches panoramas this way. Well not quite but what he does is actually combining 6 images from a fisheye in a 3D software
          Message 4 of 13 , Dec 31, 2006
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            --- In PanoToolsNG@yahoogroups.com, "Rik Littlefield" <rj.littlefield@...> wrote:

            > It is interesting to notice that if you start with camera images from
            > a perfect rectilinear lens, then in theory the entire viewing
            > pipeline can be done without any spherical trig at all! All this
            > lat/lon stuff is just a convenient way to think about the
            > calculation. Ultimately, what's being accomplished is only to
            > project each planar camera image onto the planar viewscreen. That
            > process requires only matrix multiply and perspective division, using
            > homogeneous coordinates. I'm not aware of any software that actually
            > takes this approach, however.

            The fact is there is a guy who stitches panoramas this way.
            Well not quite but what he does is actually combining 6 images from a fisheye in a 3D
            software (CINEMA 4D). They are converted to rectilinear and cropped to 90x90 degree + a
            seam area.
            He also use a 15mm fisheye the same way but they have to be combined for each
            cubeface.

            His Name is Toshio Fuji
            http://www.11moon.com/

            You would know him if you were on the Quicktime list.

            But be prepared if you contact him. He is a very special guy.
            He also designs his own panorig and this is what he did to demonstate that his rig was the
            best.
            http://www.11moon.com/QuickTimeVR/temp/crush_test_s.mov


            Hans
            www.panoramas.dk
          • georgesur2003
            I use standalone versions of SPi-V and DevalVR to view equirectangular versions of 360x180 panos. I don t know whether or not they build on the fly cubic
            Message 5 of 13 , Jan 1, 2007
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              I use standalone versions of SPi-V and DevalVR to view equirectangular
              versions of 360x180 panos.

              I don't know whether or not they build "on the fly" cubic faces...

              BTW, the displayed rectilinear image is good and moves are very smooth.
              This is very helpful for previews before end of stitcher use, but this
              is out of topic!
            • Erik Krause
              Hallo, Hannes ... Search for Euler Angles if you want to know the math behind it... -- Erik Krause Resources, not only for panorama creation:
              Message 6 of 13 , Jan 1, 2007
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                Hallo, Hannes
                on Sat, 30 Dec 2006 09:00:12 -0000 Rik wrote:

                > I forget the exact formulas. You can find the general forms in any
                > good computer graphics text, but working out the details is always
                > fiddly.

                Search for "Euler Angles" if you want to know the math behind it...

                --
                Erik Krause
                Resources, not only for panorama creation:
                http://www.erik-krause.de/
              • John Riley
                My memory of Euler Angles had grown fuzzy with time (hey, I haven t really worried about them since my mechanics classes in physics grad school 20+ years
                Message 7 of 13 , Jan 1, 2007
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                  My memory of Euler Angles had grown fuzzy with time (hey, I haven't
                  really worried about them since my mechanics classes in physics grad
                  school 20+ years ago), so I googled them to remind myself. I got a
                  kick out of the blue-boxed warning at the beginning of the article on
                  Wikpedia. You know, the same one where they say that the article may
                  need to be cleaned up or doesn't provide proper references. This one
                  said: "This article or section may be confusing or unclear for some
                  readers." I had to laugh 8-) I know I can imaging an unsuspecting
                  reader wondering what the heck THAT is!

                  John


                  John Riley
                  johnriley@...
                  jriley@...




                  On Jan 1, 2007, at 12:06 PM, Erik Krause wrote:
                  >
                  >
                  > Search for "Euler Angles" if you want to know the math behind it...
                  >
                  > --
                  > Erik Krause
                  > Resources, not only for panorama creation:
                  > http://www.erik-krause.de/
                  >
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