  Although for many solar physics problems the desirable or meaningful boundary
is the radial component of the magnetic field $B_{\rm r}$, the most readily
available measurement is the component of the magnetic field along the
line-of-sight to the observer, $B_{\rm los}$. As this component is only equal
to the radial component where the viewing angle is exactly zero, some
approximation is required to estimate $B_{\rm r}$ at all other observed
locations. In this study, a common approximation known as the
"$\mu$-correction", which assumes all photospheric field to be radial, is
compared to a method which invokes computing a potential field that matches the
observed $B_{\rm los}$, from which the potential field radial component,
$B_{\rm r}^{\rm pot}$ is recovered. We demonstrate that in regions that are
truly dominated by radially-oriented field at the resolution of the data
employed, the $\mu$-correction performs acceptably if not better than the
potential-field approach. However, it is also shown that for any solar
structure which includes horizontal fields, i.e. active regions, the
potential-field method better recovers both the strength of the radial field
and the location of magnetic neutral line.
