Re: [Plplot-general] peculiar "segmented" fills using shade plots / plplot 5.8.0 & 5.9.0

[David S. <dj...@ca...>]

On 15 Nov 2008, at 02:06, Hezekiah M. Carty wrote:

> On Fri, Nov 14, 2008 at 7:59 PM, David Seery <dj...@ca...> wrote:
>> I would like to produce contour plots in which the contours are  
>> filled
>> with a solid colour. Unfortunately, ... calls to plshades
>> produce weirdly segmented images, in which the solid fill is broken  
>> up
>> with unwanted lines, like this:
>>
>> http://www.damtp.cam.ac.uk/user/djs61/figures.pdf
>
> This is, at least in part, due to the fact the the plshade functions
> in PLplot draw the filled contours as a series of polygons.

Thanks very much for your helpful and comprehensive answer. I had  
tried to exclude this possibility by checking the output of the png  
driver, but clearly some mishap occurred (perhaps I looked at the  
wrong file by mistake).

> Vector-based file output (including your example PDF) does not exhibit
> this trait if it is viewed from gv with anti-aliasing disabled.
> Evince (the default PDF viewer in Ubuntu/Gnome) anti-aliases its
> output and does show these inter-polygon lines.  I do not know if
> these lines show up on a printed version of these PDFs.

They don't show up on printed versions, at least on those printers I  
have access to. The anti-aliasing shows up in the same way using  
Apple's Preview, which is partly what made me think the effect was real.

> I have seen this same issue in output from other plotting packages as
> well.  One possible workaround is to plot the shaded regions as a
> bitmap embedded in the PS/PDF/SVG output.  PLplot does not have
> support for this directly at this time.  However, you can accomplish
> this with extra effort using the extcairo driver and a few Cairo
> tricks.  I can go in to how to do this in more detail if desired.

That would be extremely useful if it were possible! I'm trying to  
produce a graph which is scalable and can be embedded within another  
document. It probably won't be possible to turn anti-aliasing off when  
the document is viewed, so this would otherwise seem to be an  
insurmoutable obstacle. I'm slightly perplexed, because I am sure I  
have seen plplot output before which contains contiguous shaded regions.

Thanks very much,
David