Re: semicircular "no go" area

Bill J Gray Jul 10, 2003

Hi Alan,

That's odd... two possible reasons come to mind.

First, if the number of points was changed from 16 to,
say, 8, you would get half of the points drawn, then
closed off to the starting point... that is, a semicircle.

Second, I see that in some projections, you get a
semicircle or semicircle-like shape. For example,
set "simple cylindrical" with "zenith up", and you
get something close to a semicircle. This simply
reflects the fact that all projections introduce extreme
distortion somewhere. The default (stereographic)
projection causes essentially infinite distortion in
scale, but puts it all conveniently on the far side
of the sky from the chart center. Most of the other
projections aren't so polite about this.

-- Bill