for ir = 1:21
    for ith = 1:61
        r = (ir-1)*0.05;
        th = (ith-1)*(pi/180);
        x(ir,ith) = r*cos(th);
        y(ir,ith) = r*sin(th);
        c(ir,ith) = r*th;
    end
end
pcolor(x,y,c)
shading interp
hold on
contour(x,y,c,'k-')
colorbar
axis equal tight