In a position-direction measuring apparatus that is in principle incapable of
determining a true position among two positions which are point symmetrical with
respect to a certain point, the invention intends to reduce the possibility of
an error and to enable arbitrary setting of the hemisphere at the start of measurement.
The invention provides such apparatus including a unit for setting an initial position
among two points, a unit for setting a reference position based on a past measurement
result, a unit for determining positions of point symmetrical two points from a
measurement value, a unit for determining respective distances from the reference
position to the point symmetrical two points, and a unit for selecting a position,
among the positions of the point symmetrical two points, corresponding to a shorter
one of thus determined distances, as a current measurement result.
