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Re: Different coordinate systems for 1 Image used twice?

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  • dbsprometheus
    Thats what I thought, thanks ... info can ... don t ... you to add ... for you ... twice? ... it, ... (at ... building ... to ...
    Message 1 of 5 , Apr 1 7:54 AM
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      Thats what I thought, thanks





      --- In wcsml@y..., "Adam Hauldren" <adam@N...> wrote:
      > AFAIK, that's the only way of doing it, since the georeferencing
      info can
      > only be stored once per image.
      > Whether WCS/VNS actually needs to store 2 copies of the rgb info, I
      don't
      > know, but you will have to add another copy of the image to allow
      you to add
      > your false georefs.
      >
      > Regards
      >
      > Adam
      > He who hopes someone else can come up with a more elegant solution
      for you
      > ;)
      >
      > > -----Original Message-----
      > > From: dbsprometheus [mailto:dbsprometheus@y...]
      > > Sent: 31 March 2002 00:45
      > > To: wcsml@y...
      > > Subject: [WCS] Different coordinate systems for 1 Image used
      twice?
      > >
      > >
      > > I have an Orthophoto I'd like to use at least twice in my scene -
      > > Obviously on the ground, then to texture the building roofs.
      > >
      > > The Ground texture is fine, but I'd like to clone the coordinate
      > > system I am using for the ground, then add some false northing to
      it,
      > > and use that texture for the building roofs - in hopes of helping
      (at
      > > least to some degree) the distortion in the ortho because of
      building
      > > height.
      > >
      > > Any ideas - I can do it by duplicating the image, but would hate
      to
      > > do that.
      > >
      > > - Thanks
      > >
      > >
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    • James A. Zack
      ... This approach will not work very well since the radial displacement of building roofs will not be linear across the entire image. There are several
      Message 2 of 5 , Apr 1 8:19 AM
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        dbsprometheus wrote:

        > I have an Orthophoto I'd like to use at least twice in my scene -
        > Obviously on the ground, then to texture the building roofs.
        >
        > The Ground texture is fine, but I'd like to clone the coordinate
        > system I am using for the ground, then add some false northing to it,
        > and use that texture for the building roofs - in hopes of helping (at
        > least to some degree) the distortion in the ortho because of building
        > height.
        >

        This approach will not work very well since the radial displacement of building roofs
        will not be linear across the entire image. There are several factors that will make
        the displacement non linear:

        1. Focal length of the acquisition camera (longer lenses have less displacement)
        2. Height above the terrain (lower camera positions produce more displacement)
        3. Planimetric distance of building base from principle point of photo (peripheral
        buildings will have more displacement)
        4. Height of roof above base (taller buildings will have more displacement)
        5. Direction of building base from principle point of photo (displacement is always
        away from the principle point).

        Only items 1 and 2 are constant. The rest all introduce nonlinearities into either
        the displacement direction and distance.

        See the latest issue of Photogrammetric Engineering and Remote Sensing (PE&RS) May
        2002 for a good article on a method for "undisplacing" rooftops and building facades
        to recover hidden ground features to produce true orthophotos of urban environments.

        I suggest as an alternative that you create a rooftop texture image by cutting and
        pasting (scaling may be necessary for tall buildings) the rooftop portions of your
        "ortho" to their correct planimetric location (ie, on top of the building base).

        Cheers,
        Zack

        >
        > Any ideas - I can do it by duplicating the image, but would hate to
        > do that.
        >
        > - Thanks
        >
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      • Chris 'Xenon' Hanson
        ... That s the only way to do it. What you re trying to do would definitely qualify as a misuse of georeferencing, and we don t try to support it. ;) You
        Message 3 of 5 , Apr 1 8:54 AM
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          dbsprometheus wrote:

          > I have an Orthophoto I'd like to use at least twice in my scene -
          > Obviously on the ground, then to texture the building roofs.
          > The Ground texture is fine, but I'd like to clone the coordinate
          > system I am using for the ground, then add some false northing to it,
          > and use that texture for the building roofs - in hopes of helping (at
          > least to some degree) the distortion in the ortho because of building
          > height.
          > Any ideas - I can do it by duplicating the image, but would hate to
          > do that.


          That's the only way to do it. What you're trying to do would definitely
          qualify as a 'misuse' of georeferencing, and we don't try to support it. ;)

          You will end up with two copies of the image in memory.

          > - Thanks

          Chris - Xenon
          --
          Chris Hanson | Xenon@... | I've got friends in low latitudes!
          New Visual Nature Studio 1.1: http://www.3DNature.com/
          "There is no Truth. There is only Perception. To Perceive is to Exist." - Xen
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