# how to use inpolygon function

2 views (last 30 days)
Sososasa on 30 Mar 2014
Commented: Sososasa on 30 Mar 2014
Hi,
I have two polygons with different number of vertices:
polygon1= [0.1624 -0.6477;
0.2247 -0.6477;
0.2247 0.3874;
0.1624 0.5219]
polygon2= [0.1624 0.5219;
0.2247 0.3874;
0.2247 0.5651]
Where the first column is X-coordinates and the second column in Y-coordinates. I want to know if a any random point is in the first or second polygon. How can I do that? I read the documentation of this function (inpolygon) but I don't understand it well.

Jos (10584) on 30 Mar 2014
A polygon is defined by its vertices(corner points), being pairs of (x,y) coordinates. In your case, these coordinates are stored in a single N-by-2 matrix.
polygon1= [0.1624 -0.6477;
0.2247 -0.6477;
0.2247 0.3874;
0.1624 0.5219]
P = rand(1,2)/2 % we will look at 1 point, but in poly can accept multiple points!
tf = inpolygon(P(:,1), P(:,2),polygon1(:,1), polygon1(:,2))
plot(polygon1([1:end 1],1), polygon1([1:end 1],2),'b.-',P(:,1), P(:,2),'r*') % a plot is often informative
if any(tf==1),
title('Some point(s) is (are) in or on the edge of polygon 1') ;
else
title('All points are outside polygon 1') ;
end
I hope this helps.
##### 1 CommentShowHide None
Sososasa on 30 Mar 2014
Thank you a lot that really help :)