我如何在matplotlib中获得笛卡尔坐标系？

Question

我不熟悉使用Python进行绘图,并且无法真正找到问题的答案:如何在matplotlib中获得笛卡尔坐标平面？我的意思是垂直参考线(坐标轴)以箭头结束,在原点(0,0)处相交,原点位于图的中心.

考虑一下做高中地理的飞机,以下是我需要实现的完美范例:

Answer 1

这是一个老问题，但我认为在今天的 matplotlib 版本中，关键字是spins。你会这样做：

ax = plt.gca()
ax.spines['top'].set_color('none')
ax.spines['bottom'].set_position('zero')
ax.spines['left'].set_position('zero')
ax.spines['right'].set_color('none')

该链接提供了更多示例。

Answer 2

如果你只想绘制一些点,散射就是你想要的

from pylab import *

x = [0,2,-3,-1.5]
y = [0,3,1,-2.5]
color=['m','g','r','b']

scatter(x,y, s=100 ,marker='o', c=color)

show()

对于漂亮的打印(带箭头和虚线):

from pylab import *
import matplotlib.pyplot as plt

x = [0,2,-3,-1.5]
y = [0,3,1,-2.5]
color=['m','g','r','b']

fig = plt.figure()
ax = fig.add_subplot(111)

scatter(x,y, s=100 ,marker='o', c=color)

[ plot( [dot_x,dot_x] ,[0,dot_y], '-', linewidth = 3 ) for dot_x,dot_y in zip(x,y) ] 
[ plot( [0,dot_x] ,[dot_y,dot_y], '-', linewidth = 3 ) for dot_x,dot_y in zip(x,y) ]

left,right = ax.get_xlim()
low,high = ax.get_ylim()
arrow( left, 0, right -left, 0, length_includes_head = True, head_width = 0.15 )
arrow( 0, low, 0, high-low, length_includes_head = True, head_width = 0.15 ) 

grid()

show()

还有一些工作要做,但距离结果不远:

Answer 3

这是绘制笛卡尔坐标系的另一种方法，基于已经给出的答案。

import numpy as np                 # v 1.19.2
import matplotlib.pyplot as plt    # v 3.3.2

# Enter x and y coordinates of points and colors
xs = [0, 2, -3, -1.5]
ys = [0, 3, 1, -2.5]
colors = ['m', 'g', 'r', 'b']

# Select length of axes and the space between tick labels
xmin, xmax, ymin, ymax = -5, 5, -5, 5
ticks_frequency = 1

# Plot points
fig, ax = plt.subplots(figsize=(10, 10))
ax.scatter(xs, ys, c=colors)

# Draw lines connecting points to axes
for x, y, c in zip(xs, ys, colors):
    ax.plot([x, x], [0, y], c=c, ls='--', lw=1.5, alpha=0.5)
    ax.plot([0, x], [y, y], c=c, ls='--', lw=1.5, alpha=0.5)

# Set identical scales for both axes
ax.set(xlim=(xmin-1, xmax+1), ylim=(ymin-1, ymax+1), aspect='equal')

# Set bottom and left spines as x and y axes of coordinate system
ax.spines['bottom'].set_position('zero')
ax.spines['left'].set_position('zero')

# Remove top and right spines
ax.spines['top'].set_visible(False)
ax.spines['right'].set_visible(False)

# Create 'x' and 'y' labels placed at the end of the axes
ax.set_xlabel('x', size=14, labelpad=-24, x=1.03)
ax.set_ylabel('y', size=14, labelpad=-21, y=1.02, rotation=0)

# Create custom major ticks to determine position of tick labels
x_ticks = np.arange(xmin, xmax+1, ticks_frequency)
y_ticks = np.arange(ymin, ymax+1, ticks_frequency)
ax.set_xticks(x_ticks[x_ticks != 0])
ax.set_yticks(y_ticks[y_ticks != 0])

# Create minor ticks placed at each integer to enable drawing of minor grid
# lines: note that this has no effect in this example with ticks_frequency=1
ax.set_xticks(np.arange(xmin, xmax+1), minor=True)
ax.set_yticks(np.arange(ymin, ymax+1), minor=True)

# Draw major and minor grid lines
ax.grid(which='both', color='grey', linewidth=1, linestyle='-', alpha=0.2)

# Draw arrows
arrow_fmt = dict(markersize=4, color='black', clip_on=False)
ax.plot((1), (0), marker='>', transform=ax.get_yaxis_transform(), **arrow_fmt)
ax.plot((0), (1), marker='^', transform=ax.get_xaxis_transform(), **arrow_fmt)

plt.show()

请注意，我没有像我的经验那样添加显示点坐标的注释，它需要更多的代码来很好地定位它们并且具有最小的重叠。要获得注释，最好使用adjustText 包或交互式图形库，例如Plotly。

Answer 4

我认为在matplotlib库中的这个例子应该让你足够接近:http: //matplotlib.org/examples/axes_grid/demo_axisline_style.html