xpos(i) in Polygonal domain

Hi, I need to define random point positions within a polygonal domain. So far, I am only able to realize the random positions of my points in the quadratic plot window with

for i=1:6000 xpos(i)=100*rand; ypos(i)=100*rand; end

So I want to arrange these points arbitrary within a polygon. I would really appreciate any help.

Answer 1

[Andrew Newell]

You could generate random points in a rectangle enclosing the polygon and then choose the points that lie inside using inpolygon. The documentation for this function even provides an example that is similar to what you want to do.

Answer 2

[Jose Jeremias Caballero]

xpos=100*rand(1,5);
ypos=100*rand(1,5);
plot([xpos xpos(1)],[ypos ypos(1)])
for i=1:length(xpos)
    text(xpos(i),ypos(i),[num2str(xpos(i)),',',num2str(ypos(i))])
end

Answer 3

[Hamid]

Dear Jose,

I am not really sure, whether this is the solution for my problem. Probably I didn't phrase it well. I need to define 6000 points within a ploygon domain! The polygon should be fixed and predefined with 8 edges.

Answer 4

[Jose Jeremias Caballero]

   %random_polygon
  xpos=100*rand(1,6000);
  ypos=100*rand(1,6000);
  xmin=min(xpos)-2; ymin=min(ypos)-2;
  xmax=max(xpos)+2; ymax=max(ypos)+2;
  X=[xmin xmin xmax xmax xmin];
  Y=[ymin ymax ymax ymin ymin];
  plot(X,Y) 
  for i=1:length(xpos)
      text(xpos(i),ypos(i),'*')
  end

[Hamid]

Dear Jose, First let me thank you for your efforts to help me.

This answer gives me a random polygon. I already have a ploygon defined as

X=[10 30 41 50 65 70 40 15 5 10];

Y=[37 35 15 10 15 37 58 60 50 37];

plot(X,Y)

But I want to define my random points so that they are inside this polygon.

Answer 5

[Jose Jeremias Caballero]

a=100;
xpos=a*rand(1,6000);
ypos=a*rand(1,6000);
X5 = [10 30 41 50 65 70 40 15 5 10]; 
Y5 = [37 35 15 10 15 37 58 60 50 37]; 
figure(gcf)
T=xpos<max(X5) & min(X5)<=xpos;
M=xpos(T);
N=ypos(T);
n=length(M);
for i=1:n
for j=1:n-i
if M(j)>=M(j+1)
aux=M(j);
auy=N(j);
M(j)=M(j+1);
N(j)=N(j+1);
M(j+1)=aux;
N(j+1)=auy;
end
end
end
U=N<max(Y5) & min(Y5)<N;
M1=M(U);
N1=N(U);

   for i=1:length(X5)
       normas(i)=norm([X5(i) Y5(i)]);
   end
  k=1;
   for i=1:length(M1)
       if (min(normas)<norm([M1(i) N1(i)]) &&  norm([M1(i) N1(i)])<max(normas)) 
           M2(k)=M1(i);
           N2(k)=N1(i);
           k=k+1;
       end
   end

   plot(X5,Y5)

    for i=1:length(M2)
       text(M2(i),N2(i),'*')
    end
   grid
   axis('image')
   axis([min(X5)-20 max(X5)+20 min(Y5)-20 max(Y5)+20])

Answer 6

[Jose Jeremias Caballero]

%thaks  Andrew Newell.

a=100;
xpos=a*rand(1,6000);
ypos=a*rand(1,6000);
X5 = [10 30 41 50 65 70 40 15 5 10]; 
Y5 = [37 35 15 10 15 37 58 60 50 37]; 
interno = inpolygon(xpos,ypos,X5,Y5);
plot(X5,Y5,xpos(interno),ypos(interno),'.r')