Touch identification for multi-touch technology

1. A method of operating a touch-sensing surface, the method comprising:

determining a first plurality of contact locations based on data from a first scan of the touch-sensing surface, wherein the first plurality of contact locations includes a first contact location;

determining a second plurality of contact locations based on data from a second scan of the touch-sensing surface, wherein the second plurality of contact locations includes a second contact location, and wherein the second scan is subsequent to the first scan;

identifying one or more contact locations that have not moved between the first scan and the second scan;

determining a number of contact locations based on the number of the one or more contact locations that have not moved and on the number of the first plurality of contact locations or the number of the second plurality of contact locations;

performing a first correlation process for correlating the second contact location with the first contact location if the number of contact locations is less than or equal to a first threshold number; and

performing a second correlation process for correlating the second contact location with the first contact location if the number of contact locations is greater than a second threshold number.

2. The method of claim 1 , wherein the first scan is performed during a first time period, and wherein the second scan is performed during a second time period.

3. The method of claim 1 , wherein the second threshold number is equal to the first threshold number.

4. The method of claim 1 , further comprising:

detecting at least one unmoved contact; and

excluding the at least one unmoved contact from at least one of the first correlation process or the second correlation process.

5. The method of claim 1 , wherein the first correlation process includes a least squares calculation.

6. The method of claim 5 , wherein performing the least squares calculation comprises calculating a sum of squared distances for each of a plurality of combinations, wherein each of the plurality of combinations correlates each of the second plurality of contact locations with one of the first plurality of contact locations, and wherein the sum of squared distances includes a square of a distance between each of the second plurality of contact locations and a corresponding contact location from the first plurality of contact locations.

7. The method of claim 1 , wherein the second correlation process includes a nearest neighbor calculation.

8. The method of claim 7 , wherein performing the nearest neighbor calculation comprises:

comparing the second contact location with the first contact location; and

correlating the second contact location with the first contact location in response to determining that the second contact location is within a maximum distance of the first contact location.

9. The method of claim 7 , wherein performing the nearest neighbor calculation comprises selecting from the first plurality of contact locations a contact location nearest the second contact location as the first contact location.

10. The method of claim 1 , further comprising:

assigning one of a plurality of contact identifiers to each of the first plurality of contact locations; and

assigning one of the plurality of contact identifiers to each of the second plurality of contact locations.

11. The method of claim 1 , wherein correlating the second contact location with the first contact location comprises assigning a contact identifier of the first contact location to the second contact location.

12. The method of claim 1 , further comprising:

if the number of the first plurality of contacts is less than the first threshold number, performing the first correlation process for correlating each of the second plurality of contact locations with one of the first plurality of contact locations; and

if the number of the first plurality of contacts is greater than the second threshold number, performing the second correlation process for correlating each of the second plurality of contact locations with one of the first plurality of contact locations.

13. A touch controller, comprising:

an input configured to connect the touch controller with a touch-sensing surface;

a processor coupled with the input; and

a memory coupled with the processor, wherein the memory contains instructions which, when executed by the processor, cause the touch controller to perform operations comprising:

determining a first plurality of contact locations based on data from a first scan of the touch-sensing surface, wherein the first plurality of contact locations includes a first contact location;

determining a second plurality of contact locations based on data from a second scan of the touch-sensing surface, wherein the second plurality of contact locations includes a second contact location, and wherein the second scan is subsequent to the first scan;

identifying one or more contact locations that have not moved between the first scan and the second scan;

determining a number of contact locations based on the number of the one or more contact locations that have not moved and on the number of the first plurality of contact locations or the number of the second plurality of contact locations;

performing a first correlation process for correlating the second contact location with the first contact location if the number of contact locations is less than or equal to a first threshold number; and

performing a second correlation process for correlating the second contact location with the first contact location if the number of contact locations is greater than or equal to a second threshold number.

14. The touch controller of claim 13 , wherein the touch-sensing surface is a touchscreen.

15. The touch controller of claim 13 , wherein the first scan is performed during a first time period, and wherein the second scan is performed during a second time period.

16. The touch controller of claim 13 , wherein the second threshold number is equal to the first threshold number.

17. The touch controller of claim 13 , wherein the memory further contains instructions which, when executed by the processor, cause the touch controller to perform operations comprising:

detecting at least one unmoved contact; and

excluding the at least one unmoved contact from at least one of the first correlation process or the second correlation process.

18. The touch controller of claim 13 , wherein the first correlation process includes performing a least squares calculation.

19. The touch controller of claim 18 , wherein performing the least squares calculation comprises calculating a sum of squared distances for each of a plurality of combinations, wherein each of the plurality of combinations correlates each of the second plurality of contact locations with one of the first plurality of contact locations, and wherein the sum of squared distances includes a square of a distance between each of the second plurality of contact locations and a corresponding contact location from the first plurality of contact locations.

20. The touch controller of claim 13 , wherein the second correlation process includes performing a nearest neighbor calculation.

21. The touch controller of claim 20 , wherein performing the nearest neighbor calculation comprises:

comparing the second contact location with the first contact location; and

correlating the second contact location with the first contact location in response to determining that the first contact location is within a maximum distance of the second contact location.

22. The touch controller of claim 20 , wherein performing the nearest neighbor calculation comprises correlating the second contact location with the first contact location comprises selecting from the first plurality of contact locations a contact location nearest the second contact location as the first contact location.

23. The touch controller of claim 13 , wherein the memory further contains instructions which, when executed by the processor, cause the touch controller to perform operations comprising:

assigning one of a plurality of contact identifiers to each of the first plurality of contact locations; and

assigning one of the plurality of contact identifiers to each of the second plurality of contact locations.

24. The touch controller of claim 13 , wherein correlating the second contact location with the first contact location comprises assigning a contact identifier of the first contact location to the second contact location.

25. The touch controller of claim 13 , wherein the memory further contains instructions which, when executed by the processor, cause the touch controller to perform operations comprising:

if the number of the first plurality of contacts is less than or equal to the first threshold number, performing the first correlation process for correlating each of the second plurality of contact locations with one of the first plurality of contact locations; and

if the number of the first plurality of contacts is greater than the second threshold number, performing the second correlation process for correlating each of the second plurality of contact locations with one of the first plurality of contact locations.