In Polygon Test For Convex Polygon

August 22, 2009 by Luigi Giaccari 
Filed under: Computational Geometry, Geometry 
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This is Brand new so please advise-me if problems occurs.

Here you can find an m-file with three different algorithms for inpolygon test.
Depending on the input data, the one that  is extimate to be the best will be chosen.

This version do not support the onpolygon output so tollerance is not necessary. Maybe in my next revision this feature will be added.

I’ll be very glad receiving suggestion (even on preferred sintax), questions bug reports.

SYNTAX:

 in=InPolyConvex(qx,qy,x,y)

Input:

  • qx : The points to be tested, vector [Nx1] of x coordinate.
  • qy : The points to be tested, vector [Nx1] of y coordinate.
  • x : The x coordinate of vertices of the convex polygon [Nx1] The syntax assumes that the vertices are specified in consecutive order.
  • y : The y coordinate of vertices of the convex polygon [Nx1] The syntax assumes that the vertices are specified in consecutive order.

Output:

  • in : An Nx1 logical array with IN(i) = TRUE if P(i,:) lies within the region.

Notes:

  • InPolyConvex do not support on polygon options so tollerance is not necessary.
  • InPolyConvex do not support edges input format of the polygon.

Maybe in the next revision these two feature will be added.

EXAMPLE:

%query points
Nq=100;
qx=rand(Nq,1);
qy=rand(Nq,1);
%the convex polygon: a square
x=.2+[0,.5,.5,0]';
y=.3+[0,0,.5,.5]';
in=InPolyConvex(qx,qy,x,y);
figure;
hold on
axis equal
plot(x,y)
plot(qx(in),qy(in),'.r');
plot(qx(~in),qy(~in),'.k');
legend('Polygon','Inside','Outside')

For bugs,questions,suggestions just contact me at :

giaccariluigi@msn.com

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