I'd like to plot a collection and scale the size of the collection
elements in relation to the data. My guess is that I need to use the
data transformation (ax.transData) since I would like the size of the
collection elements altered when zooming in/out.
Unfortunately, my attempt has led to weird results: the collection
offsets are shifted from the desired coordinates when using
ax.transData. Weirder still: the collection elements move *relative to
the data coordinates* when panning the figure.
I suspect that setting the collection transform to ax.transData is
somehow applying some part of the transform twice. Does anyone know
what I'm doing wrong here and how I can fix this?
Thanks!
-Tony
Attached is a toy example of what I'm trying to do. The radii of the
circles are plotted correctly, but notice the x, y coordinates don't
match the circle centers in the plot. Also, try panning the plot and
watch as the circles move relative to the tick marks.
>>> import matplotlib.pyplot as plt
>>> import matplotlib.transforms as transforms
>>> import numpy as np
>>> fig = plt.figure()
>>> ax = fig.add_subplot(111)
>>> x = [0.25, 0.75, 0.25, 0.75]
>>> y = [0.25, 0.25, 0.75, 0.75]
>>> r = 0.1 * np.ones(4)
>>> col = plt.scatter(x, y, np.pi*r**2)
>>> pts2pixels = transforms.Affine2D().scale(72.0/fig.dpi)
>>> col.set_transform(pts2pixels + ax.transData)
>>> plt.axis('equal')
>>> plt.show()
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