Coordinate input apparatus and its control method

A method of controlling a coordinate input apparatus which has a photo transmission/reception unit having a phototransmitter which projects light along a plane of an input region, and a photoreceptor which detects incoming light and is controlled by control signals to have detection periods during which the incoming light is detected, a reflector which is arranged on a rim portion of the input region, and configured to reflect incident light from the phototransmitter in the photo transmission/reception unit toward the photoreceptor in that photo transmission/reception unit, and a pointing device which includes a transmission unit configured to transmit an optical signal including information regarding a unique identifier based on a pointing operation and is used to make a pointing operation for to pointing an arbitrary position in the input region, the method comprising the steps of:

• detecting a shade formed by the pointing operation of the pointing device using the photo transmission/reception unit;
• detecting using the photoreceptor the optical signal transmitted from the transmission unit based on the pointing operation when a plurality of shades are detected in a single detection period;
• determining which one of the plurality of shades corresponds to the optical signal, in accordance with position of the plurality of shades and a position at which the optical signal is detected;
• calculating a coordinate value of the position on the basis of the determined one of the plurality of shades corresponding to the optical signal;
• and
• appending the identifier included in the optical signal to the coordinate value calculated on the basis of the determined one of the plurality of shades.

A coordinate input apparatus comprising:

• a pointing device used for a pointing operation and including a transmission unit configured to transmit based on the pointing operation an optical signal including an identifier of the pointing device;
• reception means for receiving incoming light, said reception means being controlled by control signals to have detection periods for detecting the incoming light;
• first detection means for detecting based on said reception means of a shade formed by the pointing operation device;
• second detection means for detecting based on said reception means the optical signal transmitted by the pointing of the pointing device when said first detection means detects a plurality of shades in a single detection period;
• determining means for determining which one of a plurality of shades corresponds to the optical signal, in accordance with the positions of the plurality of shades and a position at which the optical signal is detected;
• calculating means for calculating position information on the basis of the determined one of the plurality of shades corresponding to the optical signal;
• and
• association means for associating the identifier of the pointing device included in the optical signal with the position information corresponding to the determined one of the plurality of shades corresponding to the optical signal.