How to say the third selected point lies within the created geometry or not?

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Ramesh Bala 2018-7-24

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/411893-how-to-say-the-third-selected-point-lies-within-the-created-geometry-or-not

评论： Ramesh Bala 2018-7-26

close all
clc
base_x = [0 50 50 20 0  0] 
base_y = [0 0  10 10 10 0 ]
roof_x = [ 0 0 20 20 30 30]
roof_y =[ 10 50 10 50 50 10]
figure
plot(base_x, base_y,'-')
hold on
plot(roof_x, roof_y,'-')
axis([0 50 0 50])
grid on
[X,Y]=meshgrid(1:11);
[x] = ginput(2);
[x] = round(x);
fprintf ('the a1 coordinate value is %d,\n'  , x(1,1));
fprintf ('the b1 coordinate value is %d ,\n' , x(1,2));
fprintf ('the a2 coordinate value is %d,\n'  , x(2,1));
fprintf ('the b2 coordinate value is %d ,\n' , x(2,2));

How to say the third selected points a1,b1 a2,b2 lies within the created geometry ( base,roof) or not?

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Walter Roberson 2018-7-25

Question was continued at https://www.mathworks.com/matlabcentral/answers/412069-determining-point-is-within-polygon-or-outside

Adam Danz 2018-7-25

Kaleesh, I'm continuing your other thread (link above) here because this topic seems to be more relevant to the problems you're having.

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采纳的回答

Adam Danz 2018-7-24

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/411893-how-to-say-the-third-selected-point-lies-within-the-created-geometry-or-not#answer_330115

编辑：Adam Danz 2018-7-25

If I understand your question correctly, you're trying to determine if a coordinate (x,y) lies within a polygon.

First try matlab's inpolygon().

Another way to achieve that is by "ray casting". The idea is to draw a line from the (x,y) coordinate and extend it rightward until it passes all of the possible polygon edges. Then count the number of times that ray intersects with an edge of the polygon. If that number is non-zero and odd, then the coordinate (x,y) is within the polygon.

To achieve that, you'll need to loop through each edge of your polygon and determine if each line segment intersects with the virtual ray. Here's a nice tutorial on how to detect line segment intersection. And here's more info on the ray casting technique.