I would like to know, if I have this as the parameterization of a helicoid
$H(r, \phi):=\begin{pmatrix} r\cos \phi \\ r \sin\phi \\ \phi\end{pmatrix}$, $r \in[-1,1], \phi \in [0,2\pi] $
what would the boundary of the helicoid be? In my opinion it should be a helix, I have found something here https://mathinsight.org/parametrized_surface_introduction. would the boundary just be in case of r fixed, once with $1$ and once with $-1$? or how could I determine the boundary of the given parameterization?