RE: [Groff] Venn Diagram in Pic?

[Ted Harding]

On 12-Sep-07 14:12:46, Webb Roberts wrote:
> What is the easiest way to get a Venn diagram in Groff?  Pic doesn't
> seem to like overlapping shapes.
> 
> Thanks,
> Webb

It's not clear what you mean by "Pic doesn't like overlapping shapes".

There is no problem with drawing boundaries for the one-factor regions.
E.g. if you have 3 factors A, B and C you can draw a region for A, a
region for B overlapping the A region, and a third region for C
overlapping all three sub-regions within the first two.

This then defines 8 sub-regions: abc, Abc, aBc, abC, ABc, AbC, aBC
and ABC, say (where "abc" is outside all the regions you drew),
which you can label with corresponding text.

However, if you were to try to fill the three regions say with colour
or shades of grey as you draw them, then the last one drawn
(say C) will be entirely the colour or fill that you drew it
with, and this will blot out the subregions for the other
categories -- i.e. abC, AbC, aBC and ABC will all look the same.
Not that irregular shapes can be readily filled in pic anyway.

The real problem with Venn diagrams arises when you have more
than a few (say 5) factors. It is very difficult indeed (though
not impossible) to invent 5 simply-connected regions each of
which overlaps the others in all possible combinations -- 4 is
bad enough!

Best wishes,
Ted.

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Date: 12-Sep-07                                       Time: 15:44:53
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