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

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?

[KALYAN ACHARJYA]

Can you clarify, which geometry you consider? The complete plot space is from (0,0) to (50,50)

[Ramesh Bala]

This is the geometry , a polygonal 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]

[Walter Roberson]

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

[Adam Danz]

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

Answer 1

[Adam Danz]

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.

[Ramesh Bala]

whether this function can help or inpolygon can do? Because my idea is just to check whatever the ginput points I select should say it's within the specified plotted profile or not?

[Adam Danz]

Yes, inpolygon() is definitely worth a try. In fact, I'll add that to my answer. Matlab's documentation is self-explanatory. You just enter the (x,y) coordinates of your mouse clicks and the (x,y) coordinates of your polygon and the output is a logical indicating in/out of bounds.

[Adam Danz]

Kaleesh, inpolygon() does work.

To test if the 2 mouse-click coordinates are within the lower rectangle,

[in1 on1] = inpolygon(x(:,1), x(:,2), base_x, base_y);

and to the other shape

[in2 on2] = inpolygon(x(:,1), x(:,2), roof_x, roof_y)

Two pieces of advice. First, make your lines thicker so you can see where you shapes are. Use the 'linewidth' parameter.

plot(base_x, base_y,'-', 'LineWidth', 3)

Second, the 2nd shape you're drawing doesn't have a bottom edge. inpolygon() will still work, though.

[Ramesh Bala]

yeah the bottom edge wasn't mentioned in the previous code,but there in the updated one

xv = [0 0 0 20 20 0 10 20 20 20 20 30 30 50 50 20 30 40 50]

yv = [0 0 50 10 0 0 0 0 0 10 50 50 10 10 0 0 0 0 0 ]

let me try to check with these values now Danke /Thanks Adam

[Ramesh Bala]

yeah the command worked ,even the previous one also works. for the further case just added frpintf by calling on && in with values to check