convex != intersection

[Arnold Rots]

And so, a convex is defined by an unordered list of points, whereas a
polygon is defined by an ordered list.  A convex is a polygon -
specifically, a convex polygon.  But polygons are allowed to be concave.

  - Arnold

Roy Williams wrote:
> A convex set is one where for every pair of points in the set, the
> shortest path between them is completely contained in the set.
> 
> The intersection of two convex sets is also convex by this definition.
> 
> Perhaps the question is what is meant by a "rectangle" on the
> celestial sphere?
> 
> Roy
> 
> --------
> Caltech Center for Advanced Computing Research
> roy at cacr.caltech.edu
> 626 395 3670
> ----- Original Message ----- 
> From: "Ed Shaya" <Edward.J.Shaya.1 at gsfc.nasa.gov>
> To: <registry at ivoa.net>
> Sent: Thursday, January 29, 2004 10:12 AM
> Subject: convex != intersection
> 
> 
> >
> > Why is an intersection of coverage constraints called "convex"?
> >
> > The intersection of two rectangles may be another rectangle.  What
> is
> > convex about that?
> >
> > Ed
> >
> >
> 
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Arnold H. Rots                                Chandra X-ray Science Center
Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
60 Garden Street, MS 67                              fax:  +1 617 495 7356
Cambridge, MA 02138                             arots at head.cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
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