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Re: [fulldome] making stars

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  • Richard Joly
    ... The pinch caused by spherical projection can easily be corrected with this method: http://www.rdn.qc.ca/images/unpinching_spherical_maps.jpg To make your
    Message 1 of 17 , Jan 14, 2006
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      > I've never used this one for fulldome, the resolution is not that
      > high and the polar regions, since they are being "pinched" are an
      > issue at times, but it works fine if you are only looking at a
      > portion of the sky, as when doing standard video framed animations.

      The pinch caused by spherical projection can easily be corrected with
      this method:
      http://www.rdn.qc.ca/images/unpinching_spherical_maps.jpg

      To make your own starfield, have a look at this Photoshop tutorial from
      Greg Martin:
      http://gallery.artofgregmartin.com/tuts_arts/making_a_star_field.html

      Richard Joly
      RDN Multimedia
      6733 15e Avenue
      Montréal, Qc H1X 2V7
      514-909-4652
    • Tom Casey
      Well, not exactly... the pinching you would encounter is not what they are describing here... ours is an antialiasing issue caused by differing amounts of
      Message 2 of 17 , Jan 15, 2006
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        Well, not exactly... the pinching you would encounter is not what
        they are describing here... ours is an antialiasing issue caused by
        differing amounts of sampling in a mercator map view which causes the
        stars at the pole to look different than the ones lower on the
        dome... you need to start out with a mercator projection of the sky
        which takes into account the spherical wrapping.

        And the starfield created at the photoshop tutorial is just a random
        one, not accurately depicting the stars as we need in planetarium
        setups...


        On Jan 14, 2006, at 9:47 PM, Richard Joly wrote:

        > > I've never used this one for fulldome, the resolution is not that
        > > high and the polar regions, since they are being "pinched" are an
        > > issue at times, but it works fine if you are only looking at a
        > > portion of the sky, as when doing standard video framed animations.

        > The pinch caused by spherical projection can easily be corrected with
        > this method:
        > http://www.rdn.qc.ca/images/unpinching_spherical_maps.jpg

        > To make your own starfield, have a look at this Photoshop tutorial
        > from Greg Martin:
        > http://gallery.artofgregmartin.com/tuts_arts/making_a_star_field.html

        > Richard Joly
        > RDN Multimedia
        > 6733 15e Avenue
        > Montréal, Qc H1X 2V7
        > 514-909-4652


        ************************************************
        H o m e R u n P i c t u r e s

        Tom Casey
        President & Creative Director

        100 First Avenue - Suite 450
        Pittsburgh, PA 15222
        412-391-8200
        mailto:tom@...
        http://www.hrpictures.com
      • Tom Casey
        Here is a site with the star position data for about the 9000 brightest... it s nice because it is given in formats that can be read in some 3D applications as
        Message 3 of 17 , Jan 15, 2006
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          Here is a site with the star position data for about the 9000
          brightest... it's nice because it is given in formats that can be
          read in some 3D applications as array data. We assembled one with
          about 40,000 stars to create a more "full" look to the sky, but
          that's well beyond what the unaided eye can see, even the 9000 list
          would be beyond that... it's all about what you want to show... for
          smaller domes with less expensive projectors, less is usually better
          since you will need to make the stars small circles for resolution
          issues.

          http://astronomy.swin.edu.au/~pbourke/modelling/starpositions/


          ************************************************
          H o m e R u n P i c t u r e s

          Tom Casey
          President & Creative Director

          100 First Avenue - Suite 450
          Pittsburgh, PA 15222
          412-391-8200
          mailto:tom@...
          http://www.hrpictures.com
        • Ed Lantz
          Another starfield bitmap available for purchase/license is Axel Mellinger s photographic all-sky panorama. It is available as an Aitoff projection in galactic
          Message 4 of 17 , Jan 15, 2006
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            Another starfield bitmap available for purchase/license is Axel
            Mellinger's photographic all-sky panorama. It is available as an Aitoff
            projection in galactic coordinates or as an equidistant azimuthal
            (polar) projection. The full resolution file size is 300 MB, allowing
            spherical zooming into starfield details without image degredation. The
            brightness of the Milky Way and other deep-sky objects seem to be
            exaggerated in this image, but since the mapping is very accurate, it is
            possible to exactly overlay a synthetic starfield and fade up Axel's
            image to provide an impressive Milky Way for an otherwise sterile
            synthetic night sky.

            Axel's photographic all-sky panorama is available at:

            http://home.arcor-online.de/axel.mellinger/

            He's also get a QTVR-like interface allowing you to pan the entire
            celestial sphere and zoom in on hotspot features at:

            http://canopus.physik.uni-potsdam.de/~axm/mwpan_vr.html

            And while you're on the site, check out Axel's other astrophotography
            at:

            http://canopus.physik.uni-potsdam.de/~axm/astrophot.html


            Ed Lantz
            Visual Bandwidth, Inc.
            Email: <mailto:ed@...> ed@...
            Web: <http://www.visualbandwidth.com> www.visualbandwidth.com
          • pedrosaantonio
            Hi! I must say that Ed Lantz is quit right. We have used this image and it is suberb. With some simple work you can extract the stars from the image, keeping
            Message 5 of 17 , Jan 16, 2006
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              Hi!

              I must say that Ed Lantz is quit right.
              We have used this image and it is suberb.
              With some simple work you can extract the stars from the image,
              keeping only the Milky Way background.

              The USNO has several star catalogues available, including the Tycho-2
              star catalogue of the 2.5 Million Brightest Stars (500Mb).
              http://ad.usno.navy.mil/star/

              Antonio Pedrosa
              Navegar Foundation
            • Ka Chun Yu
              ... Just be warned that because Axel mosaicked together many multiple shots of the sky, there are blend issues. The band of the Milky Way is pretty good for
              Message 6 of 17 , Jan 16, 2006
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                Ed Lantz wrote:
                > Another starfield bitmap available for purchase/license is Axel
                > Mellinger's photographic all-sky panorama.

                Just be warned that because Axel mosaicked together many multiple
                shots of the sky, there are blend issues. The band of the Milky Way
                is pretty good for the most part, but if you look closely at regions
                outside of it, you'll find "double" stars and other overlapping
                effects.

                Also if you try to overlay an exact starfield (e.g., the HIPPARCOS
                catalog) on the Mellinger image, you'll find many regions where the
                overlap is not perfect, and hence again the issue of "double" stars.
                Again, this is probably to the use of multiple, individual plates that
                had to be geometrically corrected and then tiled together to form the
                final all-sky panorama. These problems may not be an issue if you use
                a lower resolution version of the panorama, but if you have the full
                resolution, 300 MB-sized file, you'll notice it.

                (Also Axel may have fixed many of these problems in his subsequent
                tweaking of the mosaic. You'll have to ask him to know for sure.)

                Alternatively you can create an artificial, naked eye star field using
                the Bright Star Catalogue found at Paul Bourke's site, as suggested by
                Tom. For even more stars than HIPPARCOS (which has about 115,000
                usable stars), you can play with Tycho-2 (over 2.5 million), Hubble
                Guide Star Catalog (15 million stars), or the various USNO catalogs
                (the latest compilation with >1 billion collected objects, down to
                21st magnitude). However none of these have the diffuse features that
                define the Milky Way. (I thought once that if we plotted enough
                stars, some semblance of the galaxy's nebulosity would start showing
                up; I did it with the USNO-A2.0 (about 500 million stars) but even
                that many didn't give a very good looking result.)

                The big catalogs may also have artifacts around the bright stars,
                generated from the source finder algorithms that result in fake stars
                being counted. For instance I've often noticed that bright stars in
                the DSS plates will have their diffraction spikes, halos, and ghosts
                counted as multiple additional point sources. Also because the
                centers of bright stars are so blown out, their computed positions
                from the source detection algorithms might be off by more than a
                couple arcseconds.

                Here at Denver, we use HIPPARCOS (with different minimum luminosity
                cutoffs to set different absolute numbers of visible stars for our
                various needs) with the Mellinger all-sky. To nix the problem of
                doubles when overlaying artificial stars on the photographic panorama,
                we've removed all the stars from the Mellinger images using a cosmic
                ray detection and deletion tool.

                --kachun +** Dr. Ka Chun Yu **+
                +** Curator of Space Science **+
                +** Denver Museum of Nature & Science **+
                +** 2001 Colorado, Denver, CO 80205-5798 **+
                +** kcyu@... 303-370-6394 **+
              • Ryan Wyatt
                ... Actually, in our experience dealing with his version of about six months ago, we found very accurate alignment between Mellinger s image and our digital
                Message 7 of 17 , Jan 16, 2006
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                  In reference to Axel Mellinger's all-sky, Ka-Chun wrote:

                  > Just be warned that because Axel mosaicked together many multiple
                  > shots of the sky, there are blend issues.

                  Actually, in our experience dealing with his version of about six
                  months ago, we found very accurate alignment between Mellinger's
                  image and our digital database. We could drop the Digital Universe
                  starfield on top of his image with near-perfect registration.

                  > To nix the problem of doubles when overlaying artificial stars on
                  > the photographic panorama, we've removed all the stars from the
                  > Mellinger images using a cosmic ray detection and deletion tool.

                  What tool did you use...? I only know of stuff that works on FITS
                  images. And some of the stars are rather large (i.e., non-cosmic-ray-
                  like), aren't they?


                  Ryan, a.k.a.
                  Ryan Wyatt, Science Visualizer
                  Rose Center for Earth & Space
                  American Museum of Natural History
                  79th Street at Central Park West
                  New York, NY 10024
                  212.313.7903 vox
                  212.313.7868 fax
                • Ka Chun Yu
                  ... That sounds great. I guess he did get around to fixing those problems (our version of his panorama is at least 4 years old). ... Yes I did end up using
                  Message 8 of 17 , Jan 16, 2006
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                    Ryan Wyatt wrote:
                    > In reference to Axel Mellinger's all-sky, Ka-Chun wrote:
                    >> Just be warned that because Axel mosaicked together many multiple
                    >> shots of the sky, there are blend issues.

                    > Actually, in our experience dealing with his version of about six
                    > months ago, we found very accurate alignment between Mellinger's image
                    > and our digital database. We could drop the Digital Universe starfield
                    > on top of his image with near-perfect registration.

                    That sounds great. I guess he did get around to fixing those problems
                    (our version of his panorama is at least 4 years old).

                    >> To nix the problem of doubles when overlaying artificial stars on the
                    >> photographic panorama, we've removed all the stars from the Mellinger
                    >> images using a cosmic ray detection and deletion tool.

                    > What tool did you use...? I only know of stuff that works on FITS
                    > images. And some of the stars are rather large (i.e., non-cosmic-ray-
                    > like), aren't they?

                    Yes I did end up using tools for FITS images, specifically IRAF's
                    cosmicrays package. It has options for changing the expected size of
                    the cosmic ray, so with multiple passes, one can clean all the stars
                    from the faintest to the largest (tens of pixels across) in diameter.
                    One does have to decompose the 3-color image into individual color
                    channels, save them out as FITS files, and then run them one at a time
                    through the cosmic ray removal package.

                    > Ryan, a.k.a.
                    > Ryan Wyatt, Science Visualizer

                    --kachun +** Dr. Ka Chun Yu **+
                    +** Curator of Space Science **+
                    +** Denver Museum of Nature & Science **+
                    +** 2001 Colorado, Denver, CO 80205-5798 **+
                    +** kcyu@... 303-370-6394 **+
                  • Raymond Worthy
                    To all Fulldomers or Dome-l members who sell projectors, The pace of development in this field is such that it is difficult to keep abreast of all that is
                    Message 9 of 17 , Jun 21, 2006
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                      To all Fulldomers
                      or Dome-l members who sell projectors,

                      The pace of development in this field is such that it is difficult to
                      keep abreast of all that is happening, so I am taking this method of
                      contacting you in one fell swoop.

                      In the City of Newcastle in the north east of England, there is a well
                      established museum called the Hancock Museum. The Hancock is being
                      gutted and reshaped and will arise in a new existence and is to be
                      called " The Great North Museum ".

                      A London firm , Casson Mann (http://www.cassonmann.co.uk) has been
                      engaged to see the project through The plans will include a seven metre
                      planetarium and I have been asked to see if I can fit one of my fabric
                      domes in.

                      The scheme is to be finished some time in 2008, so there is a little
                      time to think about things. If you have a digital projector which you
                      think will be suitable for a seven metre dome, or if you are developing
                      one which is scheduled to come on line next year, would you be so kind
                      as to send the appropriate details to the following person, as well as
                      to include me in the loop so I know what is going on.

                      Adriana Ferlauto, adriana@...

                      Yours faithfully,

                      Ray Worthy.
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