There is described herein a method to synchronize the position and orientation of an IGD 3D Coordinate System with the position and orientation of a 3DM 3D Coordinate System, in which the IGD's gravity direction measurement device and electronic compass are used explicitly. There is also described a method for maintaining the synchronization while the IGD is moving, in which the IGD's three-axis accelerometer is used explicitly. There is further described how an IGD, once its position and orientation have been synchronized to the position and orientation of a 3DM, can be used to display 3D graphics that guide the measurement process.