insidep

 INSIDEP  Find all the points strictly inside an interactively draw polygon
          drawn on the currently displayed plot.  The plot should be
          drawn with xg and yg as dots before.
         
   USAGE  ind=insidep(xg,yg);

           xg = x locations of points
           yg = y locations of points

   Example:  x=rand(20,1);y=rand(20,1);
             plot(x,y,'kx');
             ind=insidep(x,y);
         (then click continuously with left mouse to 
          draw polygon until done, then click right mouse
          to compute points inside.)

0001 function ind=insidep(xg,yg);
0002 % INSIDEP  Find all the points strictly inside an interactively draw polygon
0003 %          drawn on the currently displayed plot.  The plot should be
0004 %          drawn with xg and yg as dots before.
0005 %
0006 %   USAGE  ind=insidep(xg,yg);
0007 %
0008 %           xg = x locations of points
0009 %           yg = y locations of points
0010 %
0011 %   Example:  x=rand(20,1);y=rand(20,1);
0012 %             plot(x,y,'kx');
0013 %             ind=insidep(x,y);
0014 %         (then click continuously with left mouse to
0015 %          draw polygon until done, then click right mouse
0016 %          to compute points inside.)
0017 %
0018 
0019 [x,y]=draw;
0020 n=length(x);
0021 x(n+1)=x(1);
0022 y(n+1)=y(1);
0023 line(x,y,'color','cyan','linestyle','o','erasemode','none')
0024 line(x,y,'color','cyan','linestyle','-','erasemode','none')
0025 %
0026 ind=inside(xg,yg,x,y); 
0027 %
0028 %  ind=0 outside polygon
0029 %  ind=1 inside
0030 %  ind=2 on exterior edge
0031 %  ind=4 on exterior vertex
0032 %
0033 line(xg(ind==1),yg(ind==1),'color','green','linestyle','o','erasemode','none')
0034 line(xg(ind==2),yg(ind==2),'color','red','linestyle','o','erasemode','none')
0035 line(xg(ind==4),yg(ind==4),'color','white','linestyle','o','erasemode','none')
0036 %
0037 %  return indices of inside points only
0038 %
0039 ind=find(ind==1);
0040 hold off