How to determine the exact intersection between line and two curves

Question

Hossam Mosbah 2022-3-14

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1671624-how-to-determine-the-exact-intersection-between-line-and-two-curves

回答： Star Strider 2022-3-14

采纳的回答： Star Strider

matlab.mat

Data is attached.

Hi everyone,

I am trying to find the exact intersection between line and curve and I tried everything and all they gave me an approximate intersection. Can anyone help me to determine the exact intersection. Thanks in advance,

I used " intersect points=find(p1==p2)"

intersectionpoints =

0×1 empty double column vector

However, If i used intersectionpoints=find(p1>=p2)

intersectionpoints =

9 10 11 12 13 14 18 19 20 21 22

So 9 is not the exact point, it is the point after the intersection between p1 and p2, how to find the exact intersected point between the red line and the blue curve.

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Star Strider 2022-3-14

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1671624-how-to-determine-the-exact-intersection-between-line-and-two-curves#answer_917524

在 MATLAB Online 中打开

Try this —

LD = load(' matlab.mat');
p1 = LD.p1;
p2 = LD.p2;
x = linspace(0, numel(p1)-1, numel(p1));
idx = find(diff(sign(p1-p2)));                          % Approximate Indices Of The Intersections
for k = 1:numel(idx)
    idxrng = max(1,idx(k)-1) : min(numel(p1),idx(k)+1);
    xi(k) = interp1(p1(idxrng)-p2(idxrng), x(idxrng), 0);
    yi(k) = interp1(x(idxrng),p2(idxrng),xi(k));
end
Intersections = table(xi,yi)
figure
plot(x, p1,   x, p2)
hold on
plot(xi, yi, 'ms')
hold off
grid
legend('p_1','p_2','Intersections', 'Location','best')

Intersections =

4×2 table

xi yi

______ __________

7.5374 1.5534e+08

13.133 1.5534e+08

16.345 1.5534e+08

21.731 1.5534e+08

.

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

Answer 2

Torsten 2022-3-14

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1671624-how-to-determine-the-exact-intersection-between-line-and-two-curves#answer_917519

在 MATLAB Online 中打开

Depending on how you interpolate between the points of the blue curve, you will get different intersection points.

So there is no "exact" intersection you can expect to get.

If (x,y) are the points of the blue curve and y0 is the y-value of the orange curve, you can do something like:

i = 0;
for j = 1:numel(x)-1
    xl = x(j);
    yl = y(j);
    xn = x(j+1);
    yn = y(j+1);
    if yl <= y0 & yn >= y0
        i = i+1;
        xi(i) = (y0*(xn-xl)+xl*yn-xn*yl)/(yn-yl);
    end
end
xi