Re[2]: arrowheads too long in PostScript terminal

[Alan G I. <ai...@am...>]

On Wed, 22 Oct 2003, Daniel J Sebald apparently wrote:
>  user expectations
> are something to consider.  But also you should weigh
> in any preceding standards.  My guess is that there
> have been long discussions amongst graphics people
> about the topic and some standard may have emerged
> over the years.  I would consider using that as a guide.


I have not been able to find an answer at this 
level, so I took a different approach: I looked
in a number of nicely done math books to see
how arrows are drawn.

I found two widespread conventions:
i. The arrowhead ink ends right at the point the arrow is
drawn to.  This is the convention that I have been pushing
for.
ii. The arrowhead ink ends right at the edge of a filled
circle, the center of which is the point that the arrow
is drawn "to".  I find this odd conceptually, but I confess
it does produce some nice looking graphics.

I did *not* find cases where the arrowhead ink extends
beyond the point the arrow is drawn to, which is the current
gnuplot convention.  So I not only remain convinced that
current gnuplot practice is wrong at the conceptual level,
it also does not appear to be a common practice (based on my
limited "survey").

So I still think that the right thing for gnuplot to do is
ensure that the very tip of the arrowhead ink is at the
point that the arrow is drawn to.  As I have argued, it is
what the user expects, and based on a little looking around,
it seems this user expectation is in line with established
practice.

However due to case (ii) above---a case that Ethan first
drew my attention to---it seems it would also be useful to
introduce a new option for set arrow: "point", which would
work like similarly to how it does for label.  Specifically,
it would place a point and then allow for a single number
"offset" (interpreted as a shortening of the arrowlength)
which would be specified in pointsize units.  (I guess one
might be wanted at each end, in which case there could also
be an option "points" that accepts two numbers an offset,
one for each end.)

fwiw,
Alan