On 15 Nov 2008, at 02:06, Hezekiah M. Carty wrote:
> On Fri, Nov 14, 2008 at 7:59 PM, David Seery <djs61@...> wrote:
>> I would like to produce contour plots in which the contours are
>> with a solid colour. Unfortunately, ... calls to plshades
>> produce weirdly segmented images, in which the solid fill is broken
>> with unwanted lines, like this:
> 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,