Re: postscript dash patterns in parametric vs data plots

[Jonathan T. <jt...@as...>]

Hi, all,

On Mon, 29 Mar 2010, Hans-Bernhard Br?ker wrote:
> I'll venture a guess, then: the difference disappears if you use the same
> number of points for both lines, right?  I.e. if you 'set samples 2' for (a),
> the two plots will be the same.  Or if you output the sampled function to a
> data file (--> help table), and plot that in place of the inline data, the two
> plots will again be the same.

Success!  I've experimented with placing 'set samples N' for various N
near the start of my test gnuplot script, with the following results
(this is still using gnuplot 4.2.6 on my computer; I've just downloaded
gnuplot-4.4.0.tar.gz but haven't compiled/installed it yet):
	N	result
	1000	wierd dash pattern for parametric line
	300	wierd dash pattern for parametric line
	200	wierd dash pattern for parametric line
	150	almost-normal dash pattern for parametric line
		(very slightly different from that for explicit-data
		 line when viewed at high magnification)
	100	normal dash pattern for parametric line
	2	normal dash pattern for parametric line

Moreover, this now explains the apparent system-dependence (i.e.,
Ethan not being able to reproduce the problem): my personal
  $HOME/.gnuplot   file contains (among other things) 'set samples 1000'.

Question:  Ethan, do you see the wierd dash patterns (or even the
same eps file as I do?) if you put 'set samples 1000' at the start
of my gnuplot script?

In any case, I think Hans-Bernhard's guess-which-turns-out-to-be-right
supports Ethan's hypothesis
# I'm guessing that the dot-dash pattern associated with the line is re-started
# for each line segment, so if you draw a line made up of multiple segments
# (as is likely for a parametric curve) the pattern is discontinuous at each
# break point.


There is also still Mojca Miklavec's observation that on a Mac,
Apple's viewer and ps2pdf give different results when viewing the eps
file I uploaded to sourceforge.  Can anyone else on a different type
of computer try viewing the eps file I generated?  I'm at home & don't
have a postscript printer available, though I can try printing this at
work on wednesday.  Of course, some postscript printers internally
use ghostscript (just as my viewer 'gv' does), so consistency there
may not mean quite as much as one might hope.....

ciao,

-- 
-- "Jonathan Thornburg [remove -animal to reply]" <jt...@as...>
   Dept of Astronomy, Indiana University, Bloomington, Indiana, USA
   "Washing one's hands of the conflict between the powerful and the
    powerless means to side with the powerful, not to be neutral."
                                      -- quote by Freire / poster by Oxfam