1. A three-dimensional measurement apparatus comprising: a geometric model holding unit configured to hold a geometric model of a measurement object; a coarse position/orientation holding unit configured to hold information indicating a coarse position and orientation of the measurement object; a projection unit configured to project a plurality of types of patterns constituted by bright/dark contrast onto the measurement object; an imaging unit configured to image the measurement object onto which a pattern has been projected by the projection unit; a projection position calculation unit configured to compute coordinate values of the pattern on a captured image acquired by the imaging unit, based on the geometric model and the information indicating the coarse position and orientation; a distance calculation unit configured to search for a captured pattern on the captured image based on the coordinate values computed by the projection position calculation unit, and derive a distance between the imaging unit and a surface of the measurement object by corresponding the captured pattern with the projected pattern; and a position/orientation calculation unit configured to estimate the position and orientation of the measurement object using the distance derived by the distance calculation unit and the geometric model held in the geometric model holding unit, and update the information on the coarse position and orientation held in the coarse position/orientation holding unit.