[Gnuplot-info] ugly data-point rounding error

[Ryan D. <som...@ya...>]

Hi,

I realized some strange jiggling of plotlines in many
svg-gnuplot-graphics. Especially when a plot is supposed to be precise
and many datapoints are used, the problem gets worse.

Seeking
for the bug in the sourcecode, it turned out the problem is that every
datapoint to be drawn is handed over as an integer, e.g.

TERM_PUBLIC void SVG_vector (unsigned int x, unsigned int y) .

In
case of the standard-settings SVG_SCALE=1 , this means, that every
point is binned to integer-pixelvalues, rendering the whole sense of
vector-graphics useless.

Some examples where the problem is directly visible:
http://commons.wikimedia.org/wiki/File:Normal_distribution_cdf.svg
http://commons.wikimedia.org/wiki/File:Soliton_2nd_order.svg (see the grid on the ground which is supposed to be
 flat)
http://commons.wikimedia.org/wiki/File:Arcsin_plot.svg

if you don't see what I mean, take a look at the 2000px versions. Many graphics of this kind can be found on the internet.


Since
it's not a problem concerning only svg-export but a flaw rooting deep
inside gnuplot, i cant't correct it by myself. Gnuplot is used in many
scientific applications and I'm absolutely convinced, that treating
data-points as float values is the only reasonable choice. Those
terminals who only support raster-images can round the values later on,
and even they can take advantage of precisely located data-samples. As
a user, I don't know how to solve it, so I hope you can fix this in the
sourcecode. Floating-point output to svg-files with at least 3 digits
precision seems essential.

thanks in advance!



btw: did you notice inkscape's inability to interpret the "color"-attributes in gnuplot-created svg-graphics? maybe it helps to
 assign stroke- and fill-colors directly.