how to use inpolygon function

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.

Answer 1

[Jos (10584)]

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.

[Sososasa]

Thank you a lot that really help :)