Steve Baker (sbaker++at++link.com)
Mon, 6 Apr 1998 12:30:36 -0500 (CDT)
> I am trying to define the angle for my projection system and
> some people says that I can use angles until 70º, but other people
> says that more than 45º disturb and provides strange images.
> Do you know something about it?. Thanks.
(NOTE: I'm talking angle-subtended-by-screen-at-eyepoint here -
some people talk "half-angles" - make sure you know which you are
talking about)
* If you are projecting onto a FLAT screen then there is no distortion
in the image for any field of view up to some point just under 180
degrees. At or beyond 180 degrees everything screws up big time!
The Z buffer precision for objects at the edges of very wide angle
displays becomes a bit of a problem - and the kludgy way that
fog is implemented is certainly a problem with wide FOV.
* If you are projecting onto a curved screen (without some kind of
distortion correction) then in principal even a 1 degree field of
view has *some* distortion - and the maximum field of view that
you can tolerate is very much an application-specific thing.
Sometimes you can reduce the worst effects of distortion by
adjusting the controls on the projector - but you really
can't eliminate it properly by doing that.
There are ways of doing much better distortion correction
using Performer/OpenGL - but the price you pay in performance
is pretty steep. Also, the distortion correction that
is often suggested in these circumstances is never perfect
and will cause either some fuzziness or some aliasing (or
perhaps some compromise with both aliasing and fuzziness)
depending on how it is set up.
Either way, there is no 'hard' limit at either 45 or 70 degrees.
Steve Baker (817)619-8776 (Vox/Vox-Mail)
Raytheon Systems Inc. (817)619-4028 (Fax)
Work: SBaker++at++link.com http://www.hti.com
Home: SJBaker1++at++airmail.net http://web2.airmail.net/sjbaker1
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