Matplotlib 极坐标图径向轴偏移

Question

我想知道，是否可以偏移径向轴的起点或将其移到图形之外。

这是我希望达到的目标：

这就是我现在所拥有的。

我已阅读有关 SO 的文档和不同主题，但找不到任何有用的信息。这是否意味着如果没有在任何地方提及它甚至都不可能。

提前谢谢你。

编辑（添加了用于创建绘图的代码的 sn-p）：

ax = fig.add_subplot(111, projection='polar')
ax.set_theta_zero_location('N')
ax.set_theta_direction(-1)      
ax.plot(X,lines[li]*yScalingFactor,label=linelabels[li],color=color,linestyle=ls)

Answer 1

要偏移径向轴的起点：

编辑：从 Matplotlib 2.2.3 开始，有一个名为 set_rorigin 的新 Axes 方法可以做到这一点。你用原点的理论径向坐标来调用它。所以如果你调用ax.set_ylim(0, 2)和ax.set_rorigin(-1)，中心圆的半径将是绘图半径的三分之一。

Matplotlib

import numpy as np
import matplotlib.pyplot as plt

CIRCLE_RES = 36 # resolution of circle inside
def offset_radial_axis(ax):
    x_circle = np.linspace(0, 2*np.pi, CIRCLE_RES)
    y_circle = np.zeros_like(x_circle)
    ax.fill(x_circle, y_circle, fc='white', ec='black', zorder=2) # circle
    ax.set_rmin(-1) # needs to be after ax.fill. No idea why.
    ax.set_rticks([tick for tick in ax.get_yticks() if tick >= 0])
    # or set the ticks manually (simple)
    # or define a custom TickLocator (very flexible)
    # or leave out this line if the ticks are fully behind the circle

要在绘图外添加比例：

您可以在其他轴的上半部分添加一个额外的轴对象并使用它的 yaxis：

X_OFFSET = 0 # to control how far the scale is from the plot (axes coordinates)
def add_scale(ax):
    # add extra axes for the scale
    rect = ax.get_position()
    rect = (rect.xmin-X_OFFSET, rect.ymin+rect.height/2, # x, y
            rect.width, rect.height/2) # width, height
    scale_ax = ax.figure.add_axes(rect)
    # hide most elements of the new axes
    for loc in ['right', 'top', 'bottom']:
        scale_ax.spines[loc].set_visible(False)
    scale_ax.tick_params(bottom=False, labelbottom=False)
    scale_ax.patch.set_visible(False) # hide white background
    # adjust the scale
    scale_ax.spines['left'].set_bounds(*ax.get_ylim())
    # scale_ax.spines['left'].set_bounds(0, ax.get_rmax()) # mpl < 2.2.3
    scale_ax.set_yticks(ax.get_yticks())
    scale_ax.set_ylim(ax.get_rorigin(), ax.get_rmax())
    # scale_ax.set_ylim(ax.get_ylim()) # Matplotlib < 2.2.3

把它们放在一起：

（示例取自Matplotlib polar plot demo）

r = np.arange(0, 2, 0.01)
theta = 2 * np.pi * r

ax = plt.subplot(111, projection='polar')
ax.plot(theta, r)
ax.grid(True)

ax.set_rorigin(-1)
# offset_radial_axis(ax) # Matplotlib < 2.2.3
add_scale(ax)

ax.set_title("A line plot on an offset polar axis", va='bottom')
plt.show()

Answer 2

我不确定polar plot 是否可以这样调整。但这里有一个解决方法，基于the last example given here: Floating Axes。

我在代码中包含了解释性 cmets，如果你复制/粘贴它，它应该按原样运行：

import mpl_toolkits.axisartist.floating_axes as floating_axes
from matplotlib.projections import PolarAxes
from mpl_toolkits.axisartist.grid_finder import FixedLocator, \
     MaxNLocator, DictFormatter
import numpy as np
import matplotlib.pyplot as plt

# generate 100 random data points
# order the theta coordinates

# theta between 0 and 2*pi
theta = np.random.rand(100)*2.*np.pi
theta = np.sort(theta)

# "radius" between 0 and a max value of 40,000
# as roughly in your example
# normalize the r coordinates and offset by 1 (will be clear later)
MAX_R = 40000.
radius = np.random.rand(100)*MAX_R
radius = radius/np.max(radius) + 1.

# initialize figure:
fig = plt.figure()

# set up polar axis
tr = PolarAxes.PolarTransform()

# define angle ticks around the circumference:
angle_ticks = [(0, r"$0$"),
               (.25*np.pi, r"$\frac{1}{4}\pi$"),
               (.5*np.pi, r"$\frac{1}{2}\pi$"), 
               (.75*np.pi, r"$\frac{3}{4}\pi$"),
               (1.*np.pi, r"$\pi$"),
               (1.25*np.pi, r"$\frac{5}{4}\pi$"),
               (1.5*np.pi, r"$\frac{3}{2}\pi$"),
               (1.75*np.pi, r"$\frac{7}{4}\pi$")]

# set up ticks and spacing around the circle
grid_locator1 = FixedLocator([v for v, s in angle_ticks])
tick_formatter1 = DictFormatter(dict(angle_ticks))

# set up grid spacing along the 'radius'
radius_ticks = [(1., '0.0'),
                (1.5, '%i' % (MAX_R/2.)),
                (2.0, '%i' % (MAX_R))]

grid_locator2 = FixedLocator([v for v, s in radius_ticks])
tick_formatter2 = DictFormatter(dict(radius_ticks))

# set up axis:
# tr: the polar axis setup
# extremes: theta max, theta min, r max, r min
# the grid for the theta axis
# the grid for the r axis
# the tick formatting for the theta axis
# the tick formatting for the r axis
grid_helper = floating_axes.GridHelperCurveLinear(tr,
                                                  extremes=(2.*np.pi, 0, 2, 1),
                                                  grid_locator1=grid_locator1,
                                                  grid_locator2=grid_locator2,
                                                  tick_formatter1=tick_formatter1,
                                                  tick_formatter2=tick_formatter2)

ax1 = floating_axes.FloatingSubplot(fig, 111, grid_helper=grid_helper)
fig.add_subplot(ax1)

# create a parasite axes whose transData in RA, cz
aux_ax = ax1.get_aux_axes(tr)

aux_ax.patch = ax1.patch # for aux_ax to have a clip path as in ax
ax1.patch.zorder=0.9 # but this has a side effect that the patch is
                     # drawn twice, and possibly over some other
                     # artists. So, we decrease the zorder a bit to
                     # prevent this.

# plot your data:
aux_ax.plot(theta, radius)
plt.show()  

这将生成以下图：

您必须调整轴标签以满足您的需求。
我缩放了数据，因为否则会发生与您的绘图相同的问题 - 内部的空圆圈将被缩放为一个点。您可以尝试使用极坐标图进行缩放，只需将自定义标签放在径向轴上即可达到类似的效果。