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Re: [PanoToolsNG] Learned from the List

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  • Ken Warner
    Roger, you are exactly right. Cylindrical images need a cylindrical projection. Most viewers use a gnomic projection assuming that the image they are
    Message 1 of 9 , May 2, 2011
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      Roger, you are exactly right. Cylindrical images need a cylindrical
      projection. Most viewers use a gnomic projection assuming that the
      image they are projecting is a spherical image. A cylindrical image
      projected gnomically will have verticals that converge toward the poles.

      If DevalVR does handle cylindrical projections correctly, that would be a
      very good thing for architectural scenes.

      Roger D. Williams wrote:
      > On Tue, 03 May 2011 04:48:15 +0900, Briar <briar_bentley@...> wrote:
      >
      >> Amazing how quickly other peoples' situation goes to the back of our
      >> minds.
      >> The international news no longer concentrates on the efforts of the brave
      >> folk who still battle with the nuclear plants in your country. But thank
      >> goodness you still have somewhere like this to "rest and renew"
      >>
      >>
      >> My question, and admiration for your pan is how you manage to set it so
      >> there is no distortion when moving up or down. In most pans a building
      >> will
      >> "bend" towards the centre as you move higher up. In this everything
      >> remains
      >> vertical. How?
      >
      > Thanks for the feedback, Briar. Since I see from a later post that you use
      > DevalVR, as I do, I am not sure what you mean about the "bending" of
      > verticals. I have only ever seen this once with DevalVR, when I used it
      > to view a panorama taken with a rotary camera that generates cylindrical
      > projections by default. If you are taking cylindrical panoramas, then
      > DevalVR will normally default to treating them as spherical projections,
      > and this bends the verticals as you near the top and bottom of the image.
      >
      > I haven't updated DevalVR recently, so it may well be coping properly
      > with cylindrical projections by now. The author kindly provided me with
      > a version that DID handle them properly, but I overwrote it with a later
      > upgrade that lacked this ability and as I no longer generate cylindrical
      > projections I haven't done anything about it.
      >
      > Other than that I can't think what might be responsible for "bending," as
      > the verticals always remain straight even as they splay outwards on
      > looking up (and cave inwards on looking down, of course).
      >
      > As a matter of interest, the vertical were very hard to get right on this
      > panorama, as there are very few readily identifiable true verticals...
      > and mostly on rather remote sculptures.
      >
      > Roger W.
      >
    • Roger D. Williams
      On Tue, 03 May 2011 12:36:33 +0900, Ken Warner ... Yes, and there s a fairly easy (though not universally applicable) way of
      Message 2 of 9 , May 2, 2011
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        On Tue, 03 May 2011 12:36:33 +0900, Ken Warner <kwarner000@...>
        wrote:

        > Roger, you are exactly right. Cylindrical images need a cylindrical
        > projection. Most viewers use a gnomic projection assuming that the
        > image they are projecting is a spherical image. A cylindrical image
        > projected gnomically will have verticals that converge toward the poles.
        >
        > If DevalVR does handle cylindrical projections correctly, that would be a
        > very good thing for architectural scenes.

        Yes, and there's a fairly easy (though not universally applicable) way
        of differentiating between cylindrical and spherical projections. If
        the image has a width that is exactly double the height, then it is
        usually safe to assume "spherical" and if not, well, not.

        Roger W.

        --
        Work: www.adex-japan.com
      • fierodeval
        Hi Roger, Yes, DevalVR works as you wrote, if the proportion is aproximately 2:1 the projection used is spherical , if not it uses cylindrical , this is true
        Message 3 of 9 , May 3, 2011
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          Hi Roger,

          Yes, DevalVR works as you wrote, if the proportion is aproximately 2:1 the projection used is "spherical", if not it uses "cylindrical", this is true in 99% of cases. Maybe the stitching program could add an EXIF code to solve this ambiguity in the JPEG, I don't know.

          Anyway, I added the projection options in the context menu of the player since one year ago, so projection can be changed easily.

          regards!
          fiero




          --- In PanoToolsNG@yahoogroups.com, "Roger D. Williams" <roger@...> wrote:
          >
          > On Tue, 03 May 2011 12:36:33 +0900, Ken Warner <kwarner000@...>
          > wrote:
          >
          > > Roger, you are exactly right. Cylindrical images need a cylindrical
          > > projection. Most viewers use a gnomic projection assuming that the
          > > image they are projecting is a spherical image. A cylindrical image
          > > projected gnomically will have verticals that converge toward the poles.
          > >
          > > If DevalVR does handle cylindrical projections correctly, that would be a
          > > very good thing for architectural scenes.
          >
          > Yes, and there's a fairly easy (though not universally applicable) way
          > of differentiating between cylindrical and spherical projections. If
          > the image has a width that is exactly double the height, then it is
          > usually safe to assume "spherical" and if not, well, not.
          >
          > Roger W.
          >
          > --
          > Work: www.adex-japan.com
          >
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