Detecting multitouch events in an optical touch-sensitive device using touch event templates

1. A method for determining simultaneous touch events on a surface, the surface having at least one emitter and a plurality of detectors arranged around its periphery, the at least one emitter producing a plurality of optical beams received by the detectors, the touch events disturbing the optical beams, the method comprising:

determining, a priori, a set of touch event templates, each touch event template including a size of a contact area and a set of beams that would be disturbed by a touch event of the size of the contact area;

receiving information indicating which beams have been disturbed by at least one touch event;

comparing the received information indicating which beams have been disturbed to the sets of beams identified in the touch event templates;

determining an approximate location and size of a contact area of at least one touch event on the surface based on a match between the received information and a given touch event template; and

refining the approximate location of the at least one touch event to determine a precise location of the at least one touch event.

2. The method of claim 1 , wherein the sizes of the contact areas of the templates are based on a major axis length and a minor axis length.

3. The method of claim 1 , wherein the set of each touch event template includes at least two beams.

4. The method of claim 1 wherein the received information includes transmission coefficients, each transmission coefficient indicative that a transmission of one of the beams between an emitter and a detector has been disturbed.

5. The method of claim 4 , wherein refining the approximate location of the at least one touch event to determine the precise location of the at least one touch event comprises:

analyzing the transmission coefficients to determine the precise location of the at least one touch event.

6. The method of claim 5 , wherein analyzing the transmission coefficients to determine the precise location of the at least one touch event comprises:

interpolating the precise location based on the transmission coefficients.

7. The method of claim 6 , wherein the interpolation uses at least one of a difference between transmission coefficients and a ratio of transmission coefficients.

8. The method of claim 1 , wherein refining the approximate location of the at least one touch event to determine the precise location of the at least one touch event comprises:

analyzing a subset of the set of the beams associated with one of the touch event templates used to determine the at least one touch event and which were disturbed by the at least one touch event.

9. The method of claim 1 , wherein refining the approximate location of the at least one touch event to determine the precise location of the at least one touch event is based on a beam distribution of the at least one emitter associated with the beams disturbed by the at least one touch event.

10. The method of claim 1 wherein, within a touch event template, at least one of no two beams are parallel, and no two beams are sent to the same detector.

11. The method of claim 1 wherein the number of touch event templates in the set of touch event templates is reduced due to symmetry.

12. A touch sensitive device comprising:

at least one emitter and a plurality of detectors arranged around a periphery of a surface, the at least one emitter producing a plurality of optical beams received by the detectors, the touch events disturbing the optical beams;

a processor;

a non-transitory computer readable storage medium comprising computer program instructions that when executed by the processor cause the processor to:

determine, a priori, a set of touch event templates, each touch event template including a size of a contact area and a set of beams that would be disturbed by a touch event of the size of the contact area;

receive information indicating which beams have been disturbed by at least one touch event;

compare the received information indicating which beams have been disturbed to the sets of beams identified in the touch event templates;

determine an approximate location and size of a contact area of at least one touch event on the surface based on a match between the received information and a given touch event template; and

refine the approximate location of the at least one touch event to determine a precise location of the at least one touch event.

13. The device of claim 12 , wherein the expected sizes of the contact areas of the templates are based on a major axis length and a minor axis length.

14. The device of claim 12 , wherein the set of each touch event template includes at least two beams.

15. The device of claim 12 wherein the received information includes transmission coefficients, each transmission coefficient indicative that a transmission of one of the beams between an emitter and a detector has been disturbed.

16. The device of claim 15 , wherein refining the approximate location of the at least one touch event to determine the precise location of the at least one touch event comprises:

analyzing the transmission coefficients to determine the precise location of the at least one touch event.

17. The device of claim 16 , wherein analyzing the transmission coefficients to determine the precise location of the at least one touch event comprises:

interpolating the precise location based on the transmission coefficients.

18. The device of claim 17 , wherein the interpolation uses at least one of a difference between transmission coefficients and a ratio of transmission coefficients.

19. The device of claim 12 , wherein refining the approximate location of the at least one touch event to determine the precise location of the at least one touch event comprises:

analyzing a subset of the set of the beams associated with one of the touch event templates used to determine the at least one touch event and which were disturbed by the at least one touch event.

20. The device of claim 12 , wherein refining the approximate location of the at least one touch event to determine the precise location of the at least one touch event is based on a beam distribution of the at least one emitter associated with the beams disturbed by the actual touch event.

21. The device of claim 12 wherein, within a touch event template, at least one of no two beams are parallel, and no two beams are sent to the same detector.

22. The device of claim 12 wherein the number of touch event templates in the set of touch event templates is reduced due to symmetry.