This was done while the instrument was carried from point to point in a land vehicle or helicopter. The acceleration and time observations were taken independently in three mutually orthogonal planes which were oriented north-south, east-west, and in the direction of gravity. Orientation was achieved by means of gyroscopes. From the acceleration and time data, components of the instrument’s movement in each of three reference planes could be computed, and hence relative positions of points determined. Inertial surveying systems were
used in a variety of surveying applications, one of the most important being control
surveying. Drawbacks of the systems were their high initial cost, equipment that was bulky, and an overall accuracy less than that attainable with GNSS receivers. As a result, ISSs are no longer used for control surveys.