  Orientational field-dependence of the zero energy density of states (ZEDOS)
is calculated for superconductors with the polar state (line node), axial state
(point node) and 3D d-wave state. Depending on the gap topology and relative
field direction the field dependencies of ZEDOS sensitively differ, providing
us a useful and practical method to identify the gap topology. It is also
demonstrated that for d-wave state the field rotation in the basal plane shows
a sizable oscillation ~3% of ZEDOS. This is directly measurable in low-T
specific heat experiment in the mixed state.
