  The ruled surface is a typical modeling surface in computer aided geometric
design. It is usually given in the standard parametric form. However, it can
also be in the forms than the standard one. For these forms, it is necessary to
determine and find the standard form. In this paper, we present algorithms to
determine whether a given implicit surface is a rational ruled surface. A
parametrization of the surface is computed for the affirmative case. We also
consider the parametric situation. More precisely, after a given rational
parametric surface is determined as a ruled one, we reparameterize it to the
standard form.
