Contact tracking and position stability

This topic describes contact tracking and position stability for multi-touch hardware solutions.

Contact tracking between fast tapping and flicker

This issue is caused by two consecutive taps happening next to each other at different locations, and the “contact up“ on the first tap is immediately followed by a “contact down“ at a different location in the next scanning frame. A higher scanning rate can reduce the chance of this occurring.

Failure cases:

  • A user typing fast on a software keyboard with alternating key strokes (“ABABABAB…“) can cause two successive individual key strokes to be interpreted as a touch move event.

Contact tracking with merge

The contact tracking model must be robust enough to handle the situation when multiple contacts merge into a single component in the raw sensor image. To this end, a typical connected component analysis fails to work, and a level-based approach might not bring a robust solution.

The reverse of splitting from a single contact component to multiple contacts should be resolved together with the merge case. A properly treated merge/split pair can avoid the issue of contact ID switching.

Failure Cases:

  • Failure to do so can cause contact ID switching when the two fingers physically touch together. This can happen during a converge gesture.

Contact position stability

Contact position stability requires filtering to smooth the noise when touched stationary.

Failure Cases:

  • Manipulation such as pinching and rotation – unsmoothed targeting - can lead to confusion of certain gesture detection. For example, pinching can be confused with rotation.

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