Touch and motion detection using surface map, object shadow and a single camera

A method for receiving user inputs in a system, the system comprising a projector, a camera and one or more processors, the method comprising obtaining one or more pieces of positional or motional information of an object with respect to a reference surface, the object having a pre-determined reference peripheral point, the one or more pieces of positional information including one or more of the object's height above the reference surface, a three-dimensional (3D) coordinate of the object, and an answer of whether the object touches the reference surface, the one or more pieces of motional information including one or more of a time sequence of 3D coordinates, a velocity, an acceleration, a traveling direction, a time history of velocity, a time history of acceleration, and a time history of traveling direction, wherein the obtaining of the one or more pieces of positional or motional information of the object with respect to the reference surface comprises:

• obtaining a surface profile of the reference surface, and a surface map configured to map any point on an image captured by the camera to a corresponding physical location on the reference surface;
• at a time instant after the object is identified to be present, initiating a positional-information obtaining process;
• and
• arranging the projector and the camera with a positional configuration such that when the object not touching the reference surface is illuminated by spot light generated by the projector or a separate light source during the positional-information obtaining process, a part of the object's shadow formed on the reference surface along a topographical surface line is observable by the camera, and such that a length of the aforesaid part of the shadow, regarded as a camera-observed shadow length, is usable for uniquely determining the object's height above the reference surface in the positional-information obtaining process.