This invention relates to a coordinate input apparatus and method in which light from a designating tool is applied to a prescribed position on a coordinate input screen to produce a beam spot and coordinates corresponding to the beam spot are generated.  The invention further relates to a computer-readable memory storing the program code for this apparatus and method. 
Known examples of an input apparatus according to the prior art include one in which a beam spot on a screen is sensed using a CCD area sensor or linear sensor and image processing using coordinates of the center of gravity or pattern matching is executed to calculate and output coordinate values, and one in which use is made of a position sensing device referred to as a PSD (an analog device in which an output voltage corresponding to the position of the spot is obtained). 
By way of example, the specification of Japanese Patent Publication (KOKOKU) No.  7-76902 discloses an apparatus in which a beam spot produced by a parallel beam of visible light is sensed by a video camera to detect the coordinates of the beam spot and, at the same time, a control signal is sent and received in the form of infrared diffused light.  Further, the specification of Japanese Patent Application Laid-Open (KOKAI) No.  6-274266 discloses an apparatus in which coordinates are detected using a linear CCD sensor and a special optical mask. 
On the other hand, Japanese Patent No.  2503182 discloses the construction of an apparatus which uses a PSD and a method of correcting output coordinates in this apparatus. 
Improvements in the brightness of large-screen displays are continuing and, at the same time, these displays are being increased in size and provided with higher resolution. 
A small, inexpensive apparatus which uses a ring CCD and is strongly resistant to the effects of extraneous light has been proposed as such a coordinate input apparatus.  With this coordinate input apparatus, the pixels of the CCD are partitioned by computation to obtain a resolution that is 2N times the actual number of pixels.  For example, in a case where a 64-pixel CCD is used and the screen is divided into 1024 portions to accommodate a larger screen, a large-screen coordinate input apparatus can be constructed in theory if one pixel is divided into 16 portions.  However, though resolution can be raised in this case, a problem which arises is that the apparatus is readily susceptible to the effects of extraneous light, namely light other than input light from a designating tool. 
Accordingly, an object of the present invention is to provide a coordinate input apparatus, method and related computer-readable memory through which a large screen and high resolution can be obtained and coordinates can be input in highly precise fashion. 
According to the present invention, the foregoing object is attained by providing a coordinate input apparatus in which light from a designating tool is applied to a prescribed position on a coordinate input screen to produce a beam spot and coordinates corresponding to the beam spot are generated, the apparatus comprising: a plurality of sensing means provided in the vicinity of at least one coordinate axis for sensing the beam spot; correction means for correcting results of sensing from each of the plurality of sensing means; concatenation means for concatenating data that has been corrected by the correction means; and output means for outputting coordinate values corresponding to the beam spot based upon the data concatenated by the concatenation means; wherein light-receptive areas of the plurality of sensing means have overlapping portions. 
The correction means preferably corrects the results of sensing from each of the plurality of sensing means based upon reference coordinate values that have been stored in advance. 
Each of the plurality of sensing means preferably is a linear sensor comprising a plurality of optoelectronic transducers arrayed on a straight line. 
The correction means preferably corrects the results of sensing from each of the plurality of sensing means based upon inclination of second sensing means relative to first sensing means among the plurality of sensing means. 
The correction means preferably corrects the results of sensing from each of the plurality of sensing means based upon a magnification, which is for calculating coordinates, set for each of the plurality of sensing means. 
According to the present invention, the foregoing object is attained by providing a coordinate input method in which light from a designating tool is applied to a prescribed position on a coordinate input screen to produce a beam spot and coordinates corresponding to the beam spot are generated, the apparatus comprising: a correction step of correcting results of sensing from each of a plurality of sensing units provided in the vicinity of at least one coordinate axis for sensing the beam spot; a concatenation step of concatenating data that has been corrected at the correction step; and an output step of outputting coordinate values corresponding to the beam spot based upon the data concatenated at the concatenation step; wherein light-receptive areas of the plurality of sensing units have overlapping portions. 
According to the present invention, the foregoing object is attained by providing a computer-readable memory storing coordinate-input program code, in which light from a designating tool is applied to a prescribed position on a coordinate input screen to produce a beam spot and coordinates corresponding to the beam spot are generated, said program code comprising: program code of a correction step of correcting results of sensing from each of a plurality of sensing units provided in the vicinity of at least one coordinate axis for sensing the beam spot; program code of a concatenation step of concatenating data that has been corrected at the correction step; and program code of an output step of outputting coordinate values corresponding to the beam spot based upon the data concatenated at the concatenation step; wherein light-receptive areas of the plurality of sensing units have overlapping portions.