NetNews Usenet Archive 1992 #20/NN_1992_20.iso/spool/comp/graphics/9483

Internet Message Format | 1992-09-08 | 1.6 KB

Path: sparky!uunet!kithrup!stanford.edu!agate!usenet.ins.cwru.edu!magnus.acs.ohio-state.edu!cis.ohio-state.edu!ucbvax!WATSON.IBM.COM!lucas
From: [e-mail] ("Bruce Lucas")
Newsgroups: comp.graphics
Subject: 1-, 2-, and 3-point perspective
Message-ID: <[e-mail]>
Date: 6 Sep 92 16:55:37 GMT
Sender: [e-mail]
Lines: 22

1-, 2-, and 3-point perspective are all generated by the same
mapping: (x,y,z) -> (kx/z, ky/z) (where k can be chosen to suit
your purposes and, depending on the exact formulation, may depend
on lens focal length, image resolution, etc.)

Any set of parallel lines in a scene will appear to converge to
a point in the projection onto an image if they are not parallel
to the image plane.  1-point projection arises if there is only one
set of parallel lines in the scene not parallel to the image plane,
as for example in the case of a building seen face-on.  2-point projection
arises if there are two such sets of parallel lines not parallel to
the image plane, as for example in the case of a building seen from
an oblique view but where the viewer (or camera) is not tilted with
respect to the horizontal.  3-point project arises if there are three
such sets of parallel lines not parallel to the image plane, as for
example in the case of a building seen from an oblique view an where
the camera is also tilted with respect to the horizontal.  Thus 1-,
2-, and 3-point projection all arise from the same projection formula
and depend on the relationship of the viewer to the parallel lines
in the scene.

Bruce Lucas