Path: utzoo!utgpu!watserv1!watmath!att!dptg!ulysses!andante!mit-eddie!bloom-beacon!eru!hagbard!sunic!liuida!isy!lysator.liu.se!zap
From: zap@lysator.liu.se (Zap Andersson)
Newsgroups: comp.graphics
Subject: Re: Lunar Distortions
Keywords: projection, perspective, distortion
Message-ID: <417@lysator.liu.se>
Date: 27 Nov 90 11:11:15 GMT
References: <27332@cs.yale.edu> <1097@shakti.ncst.ernet.in> <9236@pasteur.Berkeley.EDU>
Sender: news@isy.liu.se (Lord of the News)
Organization: Lysator Computer Club, Linkoping University, Sweden
Lines: 71

ph@miro.Berkeley.EDU (Paul Heckbert) writes:

>musgrave-forest@CS.YALE.EDU (F. Ken Musgrave) writes:
>> A very wide-angle view of a scene with a sphere in an extreme corner of
>> the image yields a very distorted sphere in the image...

>dilip@ncst.ernet.in (Dilip Khandekar) responds:
>>   I also encountered the same problem and would be interested in any method
>>or projection-model which circumvents this problem. If the pin-hole camera
>>model is not a good model for the human eye-brain system then is there any
>>other model which is more accurate?

>Pictures generated with a standard perspective camera model only look "normal"
>if the viewing angle used during rendering matches the angle at which

[ some extremely interesteing blah blah deleted to save bandwidth...]

>curtain, human torso, ...) and there will be no artifacts of the
>projection if the projection lens matches the shooting lens, the viewer
>is right at the projector, and the surfaces are properly finished.

This rings a bell in my mind, since I once by mistake in my raytracer did
a purely 'angular' perspective model, i.e. the x axis of the display was
really the angle of the ray in the ground plane, and the 'y' coordinate was
the angle from that plane... the image looked.... different.... well, any-
body implemented some kind of 'different' perspective model? Ideally,
you would hook up the user's face to the screen via a telescopic pole,
and pull it via pneumatic cylinders to the correct viewing distance, and
the rendereing equation should of course not project onto a plane, but
onto a slightly curved ditto (i.e. a computer monitor). Now we would
hear no more whinig about perspective distorsion.... ;-)

No, seriously, anybody tried twiddling with it? I did (by mistake) in my tracer
but, well.... nah, not good... And the problem is, also, that these twiddlings
are only easy to do in raytracets, since linear-things (polygon's and such) may
get non-linear sides when you twiddle (har har for you Z-buffalos ;-)

Let me know of you found something stunning!

>---

>Related question: is there a formula relating camera lens
>focal length and angle of view?  (I would guess that such a relationship
>would not be theoretical, but would be based on praticalities,
>and would vary from manufacturer to manufacturer)

Well it very well does, doesn't it? only that the "standard" equation IS
based on the practicallity of the film being 35mm and nothing else. Doubt
that a mm is different from manufacturer to manufacturer (although I know
that inces are different from manufacturer to manufacturer ;-)

(((Yeah I'm metric - I'm from Sweden, goddamnit ;-)))

>Paul Heckbert, Computer Science Dept.
>570 Evans Hall, UC Berkeley		INTERNET: ph@miro.berkeley.edu
>Berkeley, CA 94720			UUCP: ucbvax!miro.berkeley.edu!ph





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