Re: arrowheads too long in PostScript terminal

[Daniel J S. <dan...@ie...>]

Alan G Isaac wrote:

>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.
>

Actually, this is probably just as good.  Quality publishers hire out
work to professional graphics companies who, I assume, know
appropriate conventions.

I think i and ii below are preferrable to the current arrowhead.  When
I find some time, I could draw the vector relationships and come up
with the formula for compensenting for pen width at the arrow tip.
(Perhaps digitize the drawing and make it available in a PDF file.)

Dan

>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
>  
>