Dini's surface

This is one of the surfaces of constant negative curvature. One of the prettiest in my view. It looks like a flower

Parametric form:

    x=a*cos(u)*sin(v)


    y=a*sin(u)*sin(v) 


    z=a*(cos(v)+log(tan((v/2))))+b*u

Example:

a=1,b=0.2,u={ 0,4*pi},v={0.001,2}

Here is the PoV3-source I used