I try to draw a circle in display coordinates around a point to avoid stretching when the axes are not equal. Using the pdf backend, the following code will give me a circle that is not centered on the point anymore:
#!/usr/bin/env python
# -*- coding: utf-8 -*-
import matplotlib.pyplot as plt
import matplotlib.patches as mpatches
import ipdb
fig = plt.figure()
ax = fig.add_subplot(1,1,1)
# plot two points
ax.plot((0.2,0.7),(0.5,0.5), "o")
ax.set_xlim((0,1))
# get the display coordinates
x, y = ax.transData.transform((0.2,0.5))
# plot a circle around the point
circle = mpatches.Circle((x,y),50,fill=None)
# add to figure
fig.artists.append(circle)
# save to pdf - circle will not be centered on (0.2,0.5)
fig.savefig("displaced.pdf")
# save to pdf - circle will not be centered on (0.2,0.5)
fig.savefig("displaced.pdf", dpi=fig.dpi)
# save to png - circle will not be centered on (0.2,0.5)
fig.savefig("displaced.png")
# save to png - circle will be centered on (0.2,0.5)
fig.savefig("displaced.png", dpi=fig.dpi)
# show plot - circle will be centered
plt.show(block=True)The reason for this can be found inFigureCanvasPdf.print_pdf()
def print_pdf(self, filename, **kwargs):
image_dpi = kwargs.get('dpi', 72) # dpi to use for images
self.figure.set_dpi(72) # there are 72 pdf points to an inch
such that the input dpi will be ignored and the scaling will be off at some point. It seems like RendererPDF can handle arbitrary dpi, as it uses a scaling factor to 72dpi, and a change to
self.figure.set_dpi(image_dpi)
solved my problem. I'm not sure though if this is just a typo or a quick fix to some other problem that is not documented here. If someone can ok this, I will open a pull request.
\ Edit
I guess I missunderstood the idea behind this, since I just reverted any scaling altogether. Then I don't really know, why this is happening.
I try to draw a circle in display coordinates around a point to avoid stretching when the axes are not equal. Using the pdf backend, the following code will give me a circle that is not centered on the point anymore:
The reason for this can be found in
FigureCanvasPdf.print_pdf()such that the input dpi will be ignored and the scaling will be off at some point. It seems like
RendererPDFcan handle arbitrary dpi, as it uses a scaling factor to72dpi, and a change tosolved my problem. I'm not sure though if this is just a typo or a quick fix to some other problem that is not documented here. If someone can ok this, I will open a pull request.
\ Edit
I guess I missunderstood the idea behind this, since I just reverted any scaling altogether. Then I don't really know, why this is happening.