Optical tablet stylus and indoor navigation system

Optical user input technology comprises three-dimensional (3D) input sensors and 3D location emitters to enable high-precision input in a 3D space, and the 3D location emitter may be a stylus or other writing or pointing device. Certain implementations may comprise an orientation assembly for transmitting orientation of the 3D location emitter in addition to location within a 3D space, and some implementations may also use selectively identifiable signaling from the 3D location emitters to the 3D input sensors to distinguish one 3D location emitter from another, to transmit data other data from a 3D location emitter to a 3D location sensor, or as a means of providing orientation information for the 3D location emitter with respect to the 3D location sensor. Also disclosed are position fixing, indoor navigation, and other complementary applications using 3D input sensors and/or 3D location emitters.