One size doesn't fit all with multi-touch
Multi-touch screens have become increasingly popular with the desire to add greater functionality to the user interface. Simple "button pressing" has evolved to more sophisticated interaction such as two-finger pinch-to-zoom and other complex gestures. Add to this the trend toward larger touchscreens used in collaborative, multi-user applications and the requirement for touch sensors capable of such performance is clear.
As customer demand for sophisticated touch interactivity increases, software and hardware companies working in this field must keep abreast of the technical requirements to support these advanced use cases.
Touch sensor 'finger race'
Touch sensor manufacturers are engaged in an "arms race" of sorts, each striving to achieve a greater capacity of touch points. And while this competitive escalation is instrumental in pushing the industry forward, focusing on specs alone obscures the more important issue of understanding the touch requirements of each unique application.
Some touch sensors now make it possible to utilize an unlimited number of touch points. But few applications require such robust touch interactivity. Therefore it's now more important than ever to understand how a particular touchscreen is expected to perform. Specifying the appropriate hardware and software ensures the installation will perform as it’s intended, and saves the customer from unnecessarily overspending on components that exceed the installation's requirements.
How many touch points?
Being able to track a greater number of touch points enables software developers to create increasingly complex applications, with a broader variety of gestures recognized. It also has the potential to allow "palm rejection" to be added to the system, i.e. recognizing and ignoring the presence of a large object placed on a screen as an anomalous touch resulting from a user leaning on the surface.
However, most touchscreens 20 inches and smaller are used in applications where a single user interfaces with a single display. Ten touchpoints (two hands) should be sufficient for the majority of applications using displays of this size. As touch displays become larger, more consideration must be given to the application of the touchscreen, and the number of touch points should be adjusted accordingly.
Again, in most large wall-mounted touchscreens – especially those in portrait orientation, such as wayfinders in shopping malls – the application is really designed for single-user interaction. As a consequence, 10 touch points are generally sufficient. However, large screens mounted in a landscape orientation (such as interactive white boards for classrooms and corporate meeting areas) invite interaction from multiple users, and therefore supporting at least 20 touch points is recommended.
Stepping it up
Touch interactivity requirements step up dramatically when a large touchscreen is installed horizontally in a table format. These are increasingly found in corporate, retail and leisure environments, for multi-user collaboration and interaction. On an 85-inch touch table, for example, it’s likely that four or more people may use the screen concurrently. Throw in the need to filter out "palm rejection" events and it becomes more understandable why such an installation must be capable of measuring 40 or more touch points.
Reaching beyond 40-60 touch points often surpasses useful, usable touchscreen performance for most applications. This is because the touch sensor and its associated control electronics (identifying and outputting the touches) are components in larger, more complex systems and must interface with the computer hardware, the chosen operating system, and application software. Unless all these elements of the system have been designed to work optimally with each other, the user experience will be disappointing. Simply put, what is the point of installing a state-of-the-art, 100-point touch sensing technology, outputting X-Y touch coordinates at less than five millisecond speeds, if you are marrying it up to a budget PC running integrated graphics processing, an outdated OS and poorly designed application software?
There are as many valid reasons for specifying a single or two-point touch sensing technology as there are for specifying a touchscreen capable of measuring 40 touches. The key is understanding the application and then designing the entire system (hardware and software) accordingly.
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