Excluding points in the plot of a streamslice function?

polygon1= [0.1624   -0.6477;
       0.2247   -0.6477;
       0.2247    0.3874;    
       0.1624    0.5219]
P = rand(20,2)/2 
check = 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*')

Imagine i have a fixed set of numbers (in this case they are random) and i find that there are some points inside this figure.

I create a grid for a certain domain:

xcoords=-0.2:0.01:1.2;
ycoords=-0.7:0.1:0.7;
[mesh1,mesh2]=meshgrid(xcoords,ycoords);

I also have created a corresponding U and V velocities for the meshgrid.

Now I want to plot my velocity field with the streamslice(mesh1,mesh2,U,V) function.

However, I dont want to include in my plot those points inside the polygon.

Is there a way to say to the streamslice function to not include certain points?

[Jacob]

Please I really need to know how i can omit points in my grid so the streamslice can ignore those points inside the polygon