既然您对使用Shapely感兴趣, 我能想到的最简单的获取垂直线的方法是使用parallel_offset
方法获取两条与AB平行的线并连接它们的端点:
from shapely.geometry import LineString
a = (10, 20)
b = (15, 30)
cd_length = 6
ab = LineString([a, b])
left = ab.parallel_offset(cd_length / 2, 'left')
right = ab.parallel_offset(cd_length / 2, 'right')
c = left.boundary[1]
d = right.boundary[0] # note the different orientation for right offset
cd = LineString([c, d])
CD的坐标是:
>>> c.x, c.y
(12.316718427000252, 31.341640786499873)
>>> d.x, d.y
(17.683281572999746, 28.658359213500127)
slope
是AB的斜率,那么CD的斜率为-1/slope
。这等于垂直变化与水平变化之比:dy/dx=-1/slope
。这给出了dx=-slope*dx
。通过勾股定理,你有3**2=dy**2+dx**2
。代入dx
,你就得到:
3**2=(-slope*dy)**2+dy**2
3**2=(slope**2 + 1)*dy**2
dy**2=3**2/(slope**2+1)
dy=math.sqrt(3**2/(slope**2+1))
然后你可以得到dx=-slope*dy
。最后,你可以使用dx
和dy
来得到C和D。所以代码将会是:
import math
dy = math.sqrt(3**2/(slope**2+1))
dx = -slope*dy
C[0] = B[0] + dx
C[1] = B[1] + dy
D[0] = B[0] - dx
D[1] = B[1] - dy
math.sqrt
只返回一个数,但通常存在正负平方根。C 对应于正平方根,D 对应于负平方根。)向量AB
归一化垂线
B
Vector类
,计算非常简单,阅读起来就像英语:B
距离为3
的AB
垂直的点:P1 = B + (B-A).perp().normalized() * 3
P2 = B + (B-A).perp().normalized() * 3
class Vector:
def __init__(self, x, y):
self.x = x
self.y = y
def __sub__(self, other):
return Vector(self.x - other.x, self.y - other.y)
def __add__(self, other):
return Vector(self.x + other.x, self.y + other.y)
def dot(self, other):
return self.x * other.x + self.y * other.y
def norm(self):
return self.dot(self)**0.5
def normalized(self):
norm = self.norm()
return Vector(self.x / norm, self.y / norm)
def perp(self):
return Vector(1, -self.x / self.y)
def __mul__(self, scalar):
return Vector(self.x * scalar, self.y * scalar)
def __str__(self):
return f'({self.x}, {self.y})'
A = Vector(10, 20)
B = Vector(15, 30)
AB = B - A
AB_perp_normed = AB.perp().normalized()
P1 = B + AB_perp_normed * 3
P2 = B - AB_perp_normed * 3
print(f'Point{P1}, and Point{P2}')
output:
Point(17.683281572999746, 28.658359213500127), and Point(12.316718427000252, 31.341640786499873)
def perptoy(self):
return Vector(1, 0)
def perptox(self):
return Vector(1, -10000) // any big number will do instead of -inf
AB = B - A
if (A.y == B.y):
AB_perp_normed = AB.perptox().normalized();
elif (A.x == B.x):
AB_perp_normed = AB.perptoy().normalized();
else:
AB_perp_normed = AB.perp().normalized();
其余的步骤与之前的帖子相同。
C
和D
? - wwii