[英]Points of Intersection of an Ellipse and a line after rotating ellipse by angle theta
我想在通過角度 theta 旋轉橢圓后找到橢圓和線的交點。
我已經編寫了 python 代碼來查找橢圓和直線的交點,但是在將橢圓旋轉了 theta 角后,我無法弄清楚如何找到交點。
def intersactionPoints(a,b,h,k,x1,y1,x2,y2):
#xi1, yi1, xi2, yi2 <- intersection points
xi1, yi1, xi2, yi2, aa, bb, cc, m = 0, 0, 0, 0, 0, 0, 0, 0
if x1 != x2:
m = (y2 - y1)/(x2 - x1)
c = y1 - m * x1
aa = b * b + a * a * m * m
bb = 2 * a * a * c * m - 2 * a * a * k * m - 2 * h * b * b
cc = b * b * h * h + a * a * c * c - 2 * a * a * k * c + a * a * k * k - a * a * b * b
else:
# vertical line case
aa = a * a
bb = -2.0 * k * a * a
cc = -a * a * b * b + b * b * (x1 - h) * (x1 - h)
d = bb * bb - 4 * aa * cc
# intersection points : (xi1,yi1) and (xi2,yi2)
if d > 0:
if (x1 != x2):
xi1 = (-bb + (d**0.5)) / (2 * aa)
xi2 = (-bb - (d**0.5)) / (2 * aa)
yi1 = y1 + m * (xi1 - x1)
yi2 = y1 + m * (xi2 - x1)
else:
yi1 = (-bb + (d**0.5)) / (2 * aa)
yi2 = (-bb - (d**0.5)) / (2 * aa)
xi1 = x1
xi2 = x1
return xi1, yi1, xi2, yi2
if __name__ == "__main__":
a = #major axis
b = #minor axis
h = #center x of ellipse
k = #center y of ellipse
x1 = #line coordinate x1
y1 = #line coordinate y1
x2 = #line coordinate x2
y2 = #line coordinate y2
xi1, yi1, xi2, yi2 = intersactionPoints(a,b,h,k,x1,y1,x2,y2)
如果您已經測試過軸對齊橢圓的現成解決方案,那么將定義線的點轉換為橢圓系統,找到交點,然后進行逆向轉換要簡單得多。
對於以原點為中心的橢圓和旋轉角theta
x1' = x1 * Cos(theta) + y1 * Sin(theta)
y1' = - x1 * Sin(theta) + y1 * Cos(theta)
對於以 cx、cy 為中心的橢圓:
x1' = (x1 - cx) * Cos(theta) + (y1 - cy) * Sin(theta)
y1' = - (x1 - cx) * Sin(theta) + (y1 - cy) * Cos(theta)
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