dash length for dashed contours

Hi all,

[TL;DR: is it possible to control the length of the dashes in dashed contours, if so how?]

I’d like to be able to control the length of dashes for dashed contours. My motivation is that I’m making a contour plot that uses dashes for the negative contours, and the plot needs to be a specific (small) size for the particular journal, so the small size of the plot makes the dashes look rather long and is a problem for some tight contours.

I have tried using some a dashes-style argument for the linestyles keyword of contour but I can’t get it to work (although I appreciate it is not documented as something one can do). For example I tried:

import matplotlib.pyplot as plt

import numpy as np

x = y = np.linspace(-np.pi, np.pi, 100)

X, Y = np.meshgrid(x, y)

Z = np.sin(X) * np.cos(Y)

plt.contour(x, y, Z, linestyles=[(3, 3)])

plt.show()

This fails at the point where I show (or save, doesn’t matter which backend) the plot with a PyCXX error:

TypeError: PyCXX: Error creating object of type N2Py7SeqBaseINS_6ObjectEEE from 3

I’ve fiddled with several other styles of argument and all fail in a similar way.

What I’d like to know is: is it possible to control the dash length of dashed contours at all? It seems like it should be as one can do this with lines easy enough. I looked through the code, and a dashes-style argument seems to get passed through the stack correctly, but fails when the Collection is drawn. It would be a really nice feature if this could be implemented in matplotlib.

Thanks,

Andrew

Hi all,

[TL;DR: is it possible to control the length of the dashes in dashed
contours, if so how?]

I'd like to be able to control the length of dashes for dashed contours.
My motivation is that I'm making a contour plot that uses dashes for the
negative contours, and the plot needs to be a specific (small) size for
the particular journal, so the small size of the plot makes the dashes
look rather long and is a problem for some tight contours.

I have tried using some a dashes-style argument for the linestyles
keyword of contour but I can't get it to work (although I appreciate it
is not documented as something one can do). For example I tried:

     import matplotlib.pyplot as plt
     import numpy as np
     x = y = np.linspace(-np.pi, np.pi, 100)
     X, Y = np.meshgrid(x, y)
     Z = np.sin(X) * np.cos(Y)
     plt.contour(x, y, Z, linestyles=[(3, 3)])
     plt.show()

This fails at the point where I show (or save, doesn't matter which
backend) the plot with a PyCXX error:

     TypeError: PyCXX: Error creating object of type
N2Py7SeqBaseINS_6ObjectEEE from 3

I've fiddled with several other styles of argument and all fail in a
similar way.

There seems to be a nasty tangle of bugs and obsolete documentation here. It should be perfectly simple and straightforward, but it isn't.

https://github.com/matplotlib/matplotlib/issues/1701

Eric

···

On 2013/01/22 11:50 PM, Andrew Dawson wrote:

What I'd like to know is: is it possible to control the dash length of
dashed contours at all? It seems like it should be as one can do this
with lines easy enough. I looked through the code, and a dashes-style
argument seems to get passed through the stack correctly, but fails when
the Collection is drawn. It would be a really nice feature if this could
be implemented in matplotlib.

Thanks,
Andrew

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