matplotlib.pyplot, preserve aspect ratio of the plot


Question

Assuming we have a polygon coordinates as polygon = [(x1, y1), (x2, y2), ...], the following code displays the polygon:

import matplotlib.pyplot as plt
plt.fill(*zip(*polygon))
plt.show()

By default it is trying to adjust the aspect ratio so that the polygon (or whatever other diagram) fits inside the window, and automatically changing it so that it fits even after resizing. Which is great in many cases, except when you are trying to estimate visually if the image is distorted. How to fix the aspect ratio to be strictly 1:1?

(Not sure if "aspect ratio" is the right term here, so in case it is not - I need both X and Y axes to have 1:1 scale, so that (0, 1) on both X and Y takes an exact same amount of screen space. And I need to keep it 1:1 no matter how I resize the window.)

1
43
5/29/2010 11:48:15 AM

Accepted Answer

Does it help to use:

plt.axis('equal')
77
5/29/2010 12:22:29 PM

There is, I'm sure, a way to set this directly as part of your plot command, but I don't remember the trick. To do it after the fact you can use the current axis and set it's aspect ratio with "set_aspect('equal')". In your example:

import matplotlib.pyplot as plt
plt.fill(*zip(*polygon))
plt.axes().set_aspect('equal', 'datalim')
plt.show()

I use this all the time and it's from the examples on the matplotlib website.


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