Shap3d40.dat, 40th 'shape' file for CPO3D
Round hole in a square disc, by users equation.
For information on the option for users equations, see users equations.
The equations, say g1(x,y,z), for the inner circular edge are
x = r*cos(phi), y = r*sin(phi), z = 0.
The equations, say g2(x,y,z), for the outer square edge are
x = s, y = s*tan(phi), z = 0, where phi = 0 to pi/4.
In the usual fashion we can combine these by using the general equation
g(x,y,z) = (1 - f)*g1 + f*g2,
where f goes from 0 to 1.
This reproduces g1 when f = 0, and g2 when f = 1.
To concentrate the segments near the inner edge, we can use f^2 instead of f.
Here s = 1, r = 0.25, and 3 symmetry planes are used.