Abstract: Measuring devices, processing devices, systems and methods for determining a position and/or orientation of one or more walls of a room and/or identifying a feature or opening in a wall of a room. A measuring device comprises a datum for positioning against a first wall of the room such that the measuring device has a known alignment and offset relative to the first wall; a plurality of motion sensors configured to measure rotational and linear movement of the measuring device in a body frame comprising orthogonal x, y and z axes, wherein the body frame x-axis and body frame y-axis are parallel to a datum plane defined by the datum and the body frame z-axis is perpendicular to the datum plane; and optionally a ranging module configured to measure a distance to a second wall in a ranging direction parallel to or transverse to the datum plane.