用PYTHON的PLT画了个月亮图，难得用到了圆和直线的知识

难得用上了直线，圆这些知识

以前总在想有了直角坐标为什么要学圆的极坐标，用了之后发现挺方便的

 参考 

https://deepinout.com/matplotlib/matplotlib-geometry/matplotlib-drawing-an-arc-diagram.html

https://matplotlib.org/2.1.2/gallery/index.html

import matplotlib.pyplot as plt
import matplotlib.ticker as ticker
import math
import numpy as np
plt.rcParams['axes.facecolor']='#001846'
linecolor = '#F3FF82'
mooncolor = '#F3FF82'

n=12
fig, ax = plt.subplots(1,1)
width = 3
sr = 5.7 #smallercircleframeradius
br = 7.3#biggercircleframeradius

#x1, x2, y1, y2
if n % 6 == 0:
    ax.plot([0,0],[sr,n], color = linecolor, linewidth = width)
    ax.plot([0,0],[-sr,-n], color = linecolor, linewidth = width)
else:
    ax.plot([0, 0], [br, n], color=linecolor, linewidth=width)
    ax.plot([0, 0], [-br, -n], color=linecolor, linewidth=width)
#ax.plot([3,n],[-3,-n], color = linecolor)

#画小圆对应的长线段
for y1 in range(-n, n+1, 6):
    #2。3象限
    x1 = -n
    k = y1/x1 #该直线的斜率
    #该直线与圆心在圆点，半径为r的圆的交点为 (x2, y2)
    x2 = -math.sqrt((sr*sr)/(1+k*k))#2、3象限是x2负数
    y2 = x2 * k
    ax.plot([x1, x2], [y1, y2], color=linecolor, linewidth = width)

    # 关于原点对称的对应的直线
    ax.plot([-x1, -x2], [-y1, -y2], color=linecolor, linewidth = width)

    # 画关于X轴Y轴对称的点对应的直线
    x1, y1 = y1, x1
    if x1 == 0 or x1 < 0: continue
    k = y1 / x1  # 该直线的斜率
    # 该直线与圆心在圆点，半径为r的圆的交点为 (x2, y2)
    x2 = math.sqrt((sr * sr) / (1 + k * k))  # y是负数
    y2 = x2 * k

    # 画关于X轴Y轴对称的点对应的直线
    ax.plot([x1, x2], [y1, y2], color=linecolor, linewidth = width)
    ax.plot([-x1, -x2], [-y1, -y2], color=linecolor, linewidth = width)
    ax.plot([-x1, -x2], [y1, y2], color=linecolor, linewidth = width)
    ax.plot([x1, x2], [-y1, -y2], color=linecolor, linewidth = width)

#画大圆对应的短线段
for y1 in range(-n+3, n+1, 6):
    #2。3象限
    x1 = -n
    k = y1/x1 #该直线的斜率
    #该直线与圆心在圆点，半径为r的圆的交点为 (x2, y2)
    x2 = -math.sqrt((br*br)/(1+k*k))#2、3象限是x2负数
    y2 = x2 * k
    ax.plot([x1, x2], [y1, y2], color=linecolor, linewidth = width)

    # 关于原点对称的对应的直线
    ax.plot([-x1, -x2], [-y1, -y2], color=linecolor, linewidth = width)

    # 画关于X轴Y轴对称的点对应的直线
    x1, y1 = y1, x1
    if x1 == 0 or x1 < 0: continue
    #print(x1, y1)
    k = y1 / x1  # 该直线的斜率
    # 该直线与圆心在圆点，半径为r的圆的交点为 (x2, y2)
    x2 = math.sqrt((br * br) / (1 + k * k)) #y是负数
    y2 = x2 * k
    # 画关于X轴Y轴对称的点对应的直线
    ax.plot([x1, x2], [y1, y2], color=linecolor, linewidth = width)
    ax.plot([-x1, -x2], [-y1, -y2], color=linecolor, linewidth = width)
    ax.plot([-x1, -x2], [y1, y2], color=linecolor, linewidth = width)
    ax.plot([x1, x2], [-y1, -y2], color=linecolor, linewidth = width)

#下面画月亮
base = 0.5 #月亮左边界的圆心
R = 3 #半径
#圆的参数方程
theta = np.linspace(np.pi*(1/2-1/8), np.pi*(3/2+1/8), 500)
x = base + R*np.cos(theta)
y = R*np.sin(theta)
ax.plot(x, y, color=mooncolor, linewidth = 0.0001)#画圆弧

base2 = base + 1#月亮右边界的圆心
R2 = 2.7#半径
#tx,ty是这两个圆的交点，算出交点，然后算出弧度制，画圆弧
tx = ((R**2-R2**2)+base2**2-base**2)/(2*(base2-base))
ty = math.sqrt(R**2 - (tx - base)**2)
#月亮右边界的圆心是(base2，0), 和(tx,ty)的直线转换成弧度
begin = math.atan(ty/(tx-base2))
end = 2*np.pi - begin#这里画个图就知道了，是一个大钝角，2π-begin

theta = np.linspace(begin, end, 500)
x2 = base2 + R2*np.cos(theta)
y2 = R2*np.sin(theta)
ax.plot(x2, y2, color=mooncolor, linewidth = 0.0001)

#对月亮内部进行填充
plt.fill_between(x, y, where=(-R+base < x) & (x < R+base), facecolor=mooncolor)
plt.fill_between(x2, y2, where=(-R2+base2 < x2) & (x2 < R2+base2), facecolor='#001846')

#坐标轴之类的设置
ax.xaxis.set_major_locator(ticker.MultipleLocator(2))
ax.yaxis.set_major_locator(ticker.MultipleLocator(2))

plt.gca().set_aspect(1)
plt.xlim(-n, n)
plt.ylim(-n, n)

ax.xaxis.set_major_locator(plt.NullLocator()) # 删除x轴刻度
ax.yaxis.set_major_locator(plt.NullLocator()) # 删除y轴刻度

#保存
filename = 'profile' + str(n)
plt.savefig(filename, bbox_inches='tight', dpi=800, pad_inches = 0)
plt.show(dpi=1000)