Coordinate locating method and apparatus

A coordinate locating apparatus for locating at least one touch point on a plane, comprising:

• a first detecting unit, comprising a first light emitting element and a first light receiving element, arranged at a first location of the plane;
• a second detecting unit, comprising a second light emitting element and a second light receiving element, arranged at a second location of the plane;
• a first optical element arranged along an edge of the plane for reflecting and retro-reflecting light from the first and the second light emitting elements;
• and
• a second and third optical elements arranged along two edges of the plane for performing at least one of reflecting and retro-reflecting light from the first and the second light emitting elements or light reflected from the first optical element, both of the two edges being adjacent to the edge along which the first optical element is arranged,
• wherein the at least one touch point is located on the basis of the signals corresponding to detected intensities of light received by the first and the second light receiving elements, and the signals are classified into a first group of signals and a second group of signals by comparing the detected intensities of light with a first threshold and a second threshold, the first group of signals corresponding to intensities lower than the second threshold and the second group of signals corresponding to intensities lower than the first threshold but higher than the second threshold.