In order to generate three-dimensional form data having characteristic
lines desired by a user from original three-dimensional form data, a
closed surface consisting of longitudes and meridians is arranged so as to
inscribe a three-dimensional form model, and the longitudes and the
meridians are projected to a surface of the three-dimensional form to
generate parametric curves running along the surface. Then, control points
of the parametric curves are moved to adjust the curves so that a part of
the parametric curves in correspondence to the movement of the control
point moves along the surface of the form model. The curves adjusted are
taken as three-dimensional form data of the form model.
