Xref: utzoo comp.sources.wanted:17316 comp.graphics:18921 Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!cis.ohio-state.edu!zaphod.mps.ohio-state.edu!rpi!uupsi!sunic!liuida!isy!isy.liu.se!jonas-y From: jonas-y@isy.liu.se (Jonas Yngvesson) Newsgroups: comp.sources.wanted,comp.graphics Subject: Re: Ray tracing Message-ID: Date: 28 Jun 91 15:06:58 GMT References: <383@bibsyst.UUCP> <1991Jun27.155718.625@otago.ac.nz> <9106271635.AA21398@enuxha.eas.asu.edu> Organization: Dept of EE, University of Linkoping Lines: 33 nwatson@ENUXHA.EAS.ASU.EDU (Nathan F. Watson) writes: >In article <1991Jun27.155718.625@otago.ac.nz> grahaf@otago.ac.nz writes: >>In article <383@bibsyst.UUCP>, ingar@bibsyst.UUCP (ingar) writes: >>> I'm not sure i made myself clear the last time so I try again. >>> >>> In my ray tracing program I am not able to ray trace cubes, or anything >>> that contains a strait line. > ^^^^^^ >The proposed solution involves diminishing the field-of-view angle by >moving the eye away from the viewing plane. I do not believe this will >work as any projection of a straight line (or boundary between polygonal >patches) will be mapped to a straight line on the viewing plane (and >screen) no matter how close to the viewing plane the eye happens to be. >Since the original poster states that straight lines are curved, the >field-of-view angle is not the problem. Yes it is, sort of. The problem is that you assume that the distance from the viewpoint to the viewplane is constant over the whole image. This is of course not the case, the distance are bigger in the corners than in the middle. If the viewpoint is close to the viewplane the relative difference is quite large and straight lines *will* map to curves. Moving the viewpoint away from the viewplane makes the relative difference smaller. Straight lines still maps into curves, but the curvature is usually so small that you can't see it. --Jonas -- ------------------------------------------------------------------------------ J o n a s Y n g v e s s o n Dept. of Electrical Engineering jonas-y@isy.liu.se University of Linkoping, Sweden ...!uunet!isy.liu.se!jonas-y