In this post I want to present an easy method to obtain a discrete parametrization of a surface S defined implicitly (f(x,y,z)=0).

This problem was discussed here several times, the most recent post is

http://www.mapleprimes.com/posts/207661-Isolation-Of-Sides-Of-The-Surface-On-The-Graph

S is supposed to be the boundary of a convex body having (x0,y0,z0) an interior point and contained in a ball of radius R centered at (x0,y0,z0).

Actually, the procedure also works if the body is only star-shaped with respect to the interior point, and it is also possible to plot only a part of the surface

inside a solid angle centered at (x0,y0,z0).

*Usage:*

Par3d(f, x=x0, y=y0, z=z0, R, m, n, theta1 .. theta2, phi1 .. phi2)

f is an expression depending on the variables x, y, z

x0, y0, z0 are the coordinates of the interior point

R is the radius of the ball which contains the surface,

m, n are the numbers of the grid lines which will be generated

The last two parameters are optional and are used when only a part of S will be parametrized.

The procedure **Par3d** returns a **MESH** structure M, which can be plotted with **PLOT3D(M)**.

Par3d :=proc(f,x::`=`,y::`=`,z::`=`,R,m,n,th:=0..2*Pi,ph:=0..Pi) local A,i,j, rij,fij,Cth,St