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Cyhist Mar 12 1997 B
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Date: Wed, 12 Mar 1997 08:10:44 -0500
Reply-To: "CYHIST Community Memory: Discussion list on the History of
Cyberspace" <CYHIST@MAELSTROM.STJOHNS.EDU> Sender: "CYHIST Community Memory: Discussion list on the History of
Cyberspace" <CYHIST@MAELSTROM.STJOHNS.EDU> From: Larry Sher <sher@BBN.COM>
Subject: Re: CYHIST Digest - 8 Mar 1997 to 9 Mar 1997
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Community Memory: Discussion List on the History of Cyberspace ______________________________________________________________________
>Alex McKenzie wrote:
>(Quoting Bob Bickford:)
>A true 3-D display system would probably involve some kind of solid hologram, and as far as I'm aware nobody has yet built one.
>
>A true 3D display based on a vibrating mirror was designed by Larry Sher and built at BBN Corp. many years ago. The system is called "Spacegraph" and only a few were sold. Spacegraph satisfied Bob Bickford's definition: "A true 3-D display would have the characteristic that you could move your head and/or walk around it to see more information." I have no idea if Spacegraph was the first operational system to satisfy this definition, but I've copied Larry on this message and he may add more.
OK. Alex's intro is an offer I can't refuse. One of the sources of discussion/confusion in the little bit of this thread I've read (from one issue of the digest) stems from the inadequacy of cyber-English to distinguish between the various types of "3D". Basically, there are
1. Flat single presentations, with or without movement, offering a variety of depth cues. Early rocking or rotating stick figure displays were in this category. Progress came with the addition of opacity as an additional depth cue and fancy rendering with shadows and texture. The latest versions of this category use immense processing power to provide almost unlimited motion even in the presence of complex objects.
2. Flat dual presentations, aka stereo. Stereo displays have mostly evolved along the line suggested above. All such displays have a number of problems associated with "stereo-ness": a. Some people have some visual difficulties with stereo displays and some cannot use them at all. b. (Without head tracking:) If the viewer moves laterally, the image shears laterally. If the viewer moves toward the display, the image appears to lose depth, and v.v. Thus, no two viewers see exactly the same geometry. c. With head tracking, the system is really designed for a single viewer. d. Head tilt is not allowed.
3. Autostereoscopic displays. These displays include holograms as well as sequential-multiplanar presentations like the SpaceGraph display that I designed at BBN in the mid 70's. (Incidentally, the SpaceGraph display was an evolutionary development from prior work by Alan Traub at Mitre in the 60's.) With autostereoscopic displays, no glasses are used and multiple viewers see different views but of the same under- lying reality, just as in real life. Head tilt is OK. So is viewer move- ment. Each display technology has its own limitations: Holograms lose resolution with depth. They recreate the static appearance of real-world, i.e., mostly opaque and colorful, objects well. Sequential-multiplanar displays produce inherently trans- parent images, and even when color is introduced (SpaceGraph development stopped before color was introduced), this transparency undermines attempts to realistically recreate the visual appearance of real-world objects. However, real-time interactivity is available, so such displays have many possibly applications.
An interesting, little-appreciated aspect of holographic or multiplanar displays is that a 6" figure on a TV screen can be appreciated as a person at, say, 25 feet. But a 6" figure in a holographic or multiplanar display looks like a 6" person at 3 feet. Attempts to imagine such "true 3D" displays as an evolutionary goal for TV are naive and doomed to a late appreciation of this attack of reality.
-Larry Sher
sher@bbn.com
(not a recipient of this mailing list)
______________________________________________________________________
Reply-To: "CYHIST Community Memory: Discussion list on the History of
Cyberspace" <CYHIST@MAELSTROM.STJOHNS.EDU> Sender: "CYHIST Community Memory: Discussion list on the History of
Cyberspace" <CYHIST@MAELSTROM.STJOHNS.EDU> From: Larry Sher <sher@BBN.COM>
Subject: Re: CYHIST Digest - 8 Mar 1997 to 9 Mar 1997
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit
______________________________________________________________________
Community Memory: Discussion List on the History of Cyberspace ______________________________________________________________________
>Alex McKenzie wrote:
>(Quoting Bob Bickford:)
>A true 3-D display system would probably involve some kind of solid hologram, and as far as I'm aware nobody has yet built one.
>
>A true 3D display based on a vibrating mirror was designed by Larry Sher and built at BBN Corp. many years ago. The system is called "Spacegraph" and only a few were sold. Spacegraph satisfied Bob Bickford's definition: "A true 3-D display would have the characteristic that you could move your head and/or walk around it to see more information." I have no idea if Spacegraph was the first operational system to satisfy this definition, but I've copied Larry on this message and he may add more.
OK. Alex's intro is an offer I can't refuse. One of the sources of discussion/confusion in the little bit of this thread I've read (from one issue of the digest) stems from the inadequacy of cyber-English to distinguish between the various types of "3D". Basically, there are
1. Flat single presentations, with or without movement, offering a variety of depth cues. Early rocking or rotating stick figure displays were in this category. Progress came with the addition of opacity as an additional depth cue and fancy rendering with shadows and texture. The latest versions of this category use immense processing power to provide almost unlimited motion even in the presence of complex objects.
2. Flat dual presentations, aka stereo. Stereo displays have mostly evolved along the line suggested above. All such displays have a number of problems associated with "stereo-ness": a. Some people have some visual difficulties with stereo displays and some cannot use them at all. b. (Without head tracking:) If the viewer moves laterally, the image shears laterally. If the viewer moves toward the display, the image appears to lose depth, and v.v. Thus, no two viewers see exactly the same geometry. c. With head tracking, the system is really designed for a single viewer. d. Head tilt is not allowed.
3. Autostereoscopic displays. These displays include holograms as well as sequential-multiplanar presentations like the SpaceGraph display that I designed at BBN in the mid 70's. (Incidentally, the SpaceGraph display was an evolutionary development from prior work by Alan Traub at Mitre in the 60's.) With autostereoscopic displays, no glasses are used and multiple viewers see different views but of the same under- lying reality, just as in real life. Head tilt is OK. So is viewer move- ment. Each display technology has its own limitations: Holograms lose resolution with depth. They recreate the static appearance of real-world, i.e., mostly opaque and colorful, objects well. Sequential-multiplanar displays produce inherently trans- parent images, and even when color is introduced (SpaceGraph development stopped before color was introduced), this transparency undermines attempts to realistically recreate the visual appearance of real-world objects. However, real-time interactivity is available, so such displays have many possibly applications.
An interesting, little-appreciated aspect of holographic or multiplanar displays is that a 6" figure on a TV screen can be appreciated as a person at, say, 25 feet. But a 6" figure in a holographic or multiplanar display looks like a 6" person at 3 feet. Attempts to imagine such "true 3D" displays as an evolutionary goal for TV are naive and doomed to a late appreciation of this attack of reality.
-Larry Sher
sher@bbn.com
(not a recipient of this mailing list)
______________________________________________________________________
