i am observing inexact drawing of point in matplotlib. To demonstrate the effect, two plot are appended, where the some examples of inexact drawing are marked. The file “image.jpeg” shows the effect most drastically. The points in this plot should lie on straight lines pointing towards the center. However there are small deviations.
To illustrate this with a simple example, i generated the plot “simple_example.jpeg” with the following commands:
t = linspace(0,10,200)
for i in range(200):
plot(t[i],t[i],“o”)
plot(t,t,“k”)
There, too, some examples are marked. The deviations are rather small, but still noticeable.
Is this kind of behavior known? Can i fix this somehow? Is this a bug?
This was tested with versions 0.99.3 and 1.1 on debian 6.0
Hallo,
i am observing inexact drawing of point in matplotlib.
As I remember from an earlier discussion on this, it's assumed that
these small deviations are tolerable in the agg renderer. This makes
the interactive backends more responsive at expenses of accuracy.
I can see the same deviations using the tkagg backend with mpl 1.1.0
but if I save as pdf using the save button I get an accurate rendering
(see attachment).
For speed in the Agg backend the markers are drawn once and then
copied as rasters to all of their positions. This implies that the
markers end up pixel aligned, which is the source of the error
you’re seeing. This does not happen in the vector backends.
If you want to not get this behavior, you can use scatter() instead
