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From: jwp@uwmacc.UUCP
Newsgroups: comp.unix.questions,comp.graphics
Subject: Unix plot(5) oddity:  arc()
Message-ID: <1298@uwmacc.UUCP>
Date: Thu, 26-Mar-87 16:18:39 EST
Article-I.D.: uwmacc.1298
Posted: Thu Mar 26 16:18:39 1987
Date-Received: Sat, 28-Mar-87 05:37:47 EST
Organization: UWisconsin-Madison Academic Comp Center
Lines: 13
Keywords: badly specified arcs
Xref: utgpu comp.unix.questions:1510 comp.graphics:412

I've been fiddling around for the first time with
the plot(1G,3X,5) graphics interface (4.3BSD, MicroVAX II)
and I noticed a curious thing:  arcs are specifed as three
points, rather than, say, as two points and an angle.
Now, triplets like (center, radius, angle) always specify arcs;
triplets like (center, point1, point2), as required by arc(3X),
almost *never* define a circular arc.  It's like specifying
three points for a line:  unless you compute that third
point awfully carefully, you will have a badly specified line.
Why is this implemented this way, and why isn't arc(3X) perceived
as being broken?
-- 
	Jeff Percival (jwp@salvax1)