Cursor Grabbing

Moving around the room: Cursor Grabbing

The most recent version of the Upoint remote is capable of measuring its own orientation in the fixed coordinate system spanned by Earth's Gravity and Magnetic North vectors. It is in this coordinate system that the position, size and orientation of the display are established by means of either the 2-click, 3-click or automated setup.

Since positional coordinates are not tracked by the Upoint remote, laser-like cursor control only works during times when the user is relatively stationary. That is, if the user moves more than 3 feet away from where the setup procedure was executed, the position of the remote relative to the display will no longer be known. When the user tries to control the cursor from his or her new position, it will appear that the cursor has been 'lost', since pointing to a certain spot on the display will not cause the cursor to appear at that location. This, however, is easily remedied by double-clicking the cursor control button, which sets in motion a procedure called cursor grabbing.

Cursor grabbing

A double-click on the cursor-control button will cause the build-in laser to activate, and the cursor to appear in a pre-determined spot. Ideally, this would be the top-right corner (for reasons explained below), but other positions are also possible (e.g., the position where the cursor appeared last). It is then quite natural for a user to move the laser-dot towards that pre-determined spot, in an attempt to 'grab' the cursor. Internally, the Upoint system will wait for a certain time (~1 sec) before it assumes the laser-beam is properly aimed at the pre-determined spot, and subsequently register the orientation of the remote - and of the associated pointing line.

Since the coordinates of the spot the user was asked to 'grab the cursor from' are in fact known to the system, it is now possible to construct a 3D line passing through the remote. This, however, is still not enough, since we need the relative position of the remote - not just a line on which it lies. It is here that the internal calculations for Upoint versions equipped with a laser- or an ultrasonic distance sensor differ from each other.

When use is made of a laser-sensor (capable of sensing distance along a very well defined line), not only the orientation of the pointing line is measured during cursor grabbing, but also the distance to the target. With these two measurements in hand, it is possible to completely re-establish the position of the remote with respect to the display, once more enabling laser-like cursor control.

When use is made of a cheap ultrasonic sensor (which can not be guaranteed to accurately measure the distance along the pointing line), use is made the fact that a user tends to always wield the remote at approximately the same height. Using this assumption, it is possible to intersect the afore-mentioned pointing line with a (known) horizontal plane, once again re-establishing the position of the remote relative to the display.

From the above and from the description of the 2 alternative non-automated setup-procedures (2-click and 3-click), it will be clear that the more expensive 'laser version' of Upoint is the most easy in setup and the most accurate in use. The cheaper 'ultrasonic version', on the other hand, allows for a slightly faster 'cursor grabbing' procedure (since no distance needs to be measured); for reasonably sized displays (>6') the errors in point-of-aim calculations will not be apparent to the user.