Re: [Matplotlib-users] ellipse in log-log

[John H. <jd...@gm...>]

On Mon, Oct 6, 2008 at 7:15 AM, Michael Droettboom <md...@st...> wrote:
> In 0.98 ellipse is drawn using bezier curves, which do not scale
> correctly in log-scaled plots.
>
> As an alternative, you can use a RegularPolygon with a high number of
> vertices (this is exactly what 0.91 did).

Here is some example code which compares the polygonal ellipse with
the spline version to get you started if you decide to go with the
polygonal appromximation Michal suggest:

import numpy as npy
from matplotlib import patches
from pylab import figure, show

xcenter, ycenter = 0.38, 0.52
#xcenter, ycenter = 0., 0.
width, height = 1e-1, 3e-1
angle = -30

theta = npy.arange(0.0, 360.0, 1.0)*npy.pi/180.0
x = width/2. * npy.cos(theta)
y = height/2. * npy.sin(theta)

rtheta = angle*npy.pi/180.
R = npy.array([
    [npy.cos(rtheta),  -npy.sin(rtheta)],
    [npy.sin(rtheta), npy.cos(rtheta)],
    ])


x, y = npy.dot(R, npy.array([x, y]))
x += xcenter
y += ycenter

fig = figure()
ax = fig.add_subplot(211, aspect='auto')
ax.fill(x, y, alpha=0.2, facecolor='yellow', edgecolor='yellow',
linewidth=1, zorder=1)

e1 = patches.Arc((xcenter, ycenter), width, height,
             angle=angle, linewidth=2, fill=False, zorder=2)

ax.add_patch(e1)

ax = fig.add_subplot(212, aspect='equal')
ax.fill(x, y, alpha=0.2, facecolor='green', edgecolor='green', zorder=1)
e2 = patches.Arc((xcenter, ycenter), width, height,
             angle=angle, linewidth=2, fill=False, zorder=2)


ax.add_patch(e2)

#fig.savefig('ellipse_compare.png')
fig.savefig('ellipse_compare')

show()