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Inf@Vis!

The digital magazine of InfoVis.net

Spatially Aware Visualisation
by Juan C. Dürsteler [message nº 130]

Computer screens are like a window to cyberspace, often too small and limited. Devices capable of locating themselves in the personal space of the user offer a window to 3D virtual spaces where the combination of movement and interaction opens up new possibilities for visualisation.
Handheld computer, Tungsten T, showing a listing. Photo by the author.

Handheld computers like Palm and many others are more and more present in our daily lives. Increasingly fitted with applications and possibilities they suffer, nevertheless, from a structural problem: their small screens offer a very limited window to cyberspace.

Such a practical and useful palmtop device is an ideal element for visualisation. For example, most of the calendars allow us to see the appointments for a whole month at a glance and those of a whole week in an intuitive, graphical form. But its reduced screen space appears to prevent it from more advanced uses and particularly from visually accessing large amounts of information, specially if this is three dimensional.

The mechanisms that these devices use to show more information are rather classic: scroll bars, physical buttons that allow you to change page or application, etc. In some cases you can use the digital pen to drag the information through the screen as if it were a window moving on top of a map. But in general it tends to be a tiresome method that obliges you to make many movements, sometimes difficult to control.

The idea to make the PDA be aware of its position in the reference space of the user opens up a wide range of possibilities to visualisation and interaction. These types of devices are called Spatially Aware Computers. The movement of the PDA in this space allows the user to perform a series of gestures that can be used as commands for the application. Basically we have 6 degrees of freedom i.e 6 different types of elementary movements:

  • Displacement along any of the three coordinate axes X, Y and Z (up and down, forward and backward, right and left)

  • Rotation around any of the three coordinate axes

For example, the movement of the Palmtop on a horizontal plane can be interpreted as a displacement of the “window” on a wider virtual 2D space, showing at each moment, the contents of that particular part of the visualisation bound to the user space, as if it were floating in it. Moving the PDA vertically can be used to zoom the contents of the window in and out in a kind of moving zoom.

PalmCoord_en.jpg (103297 bytes) PalmAng.jpg (97610 bytes)
Possible displacements of a rigid body according its degrees of freedom. In this case the x, y, z coordinates of the handheld are referred to the user's personal space. Composition and photo by the author. Possible rotations of a rigid body around its three coordinate axes. Here the centre of rotation lies in the handheld itself. 
Composition and photo by the author.

The same movement can be used to visualise the different layers of graphic objects in a Computer Aided Design drawing, where objects of a different nature are placed on different conceptual layers. For example on one layer you find the technical drawings of a machine, while the background colour lies on another and the annotation lies on yet another. Moving the PDA up and down you can switch from layer to layer. Moving it horizontally you can explore that particular layer in its full extension.

Tilting the PDA at a certain angle can be interpreted intuitively as creating a tilted plane on which the elements of a list can scroll “through gravity”. This way scrolling becomes a subtle movement where the tilt angle correlates with the scrolling speed. 

Some of these ideas were summarised as early as in 1993 in the article by G. FitzmauriceSituated information Spaces ans Spatially Aware Laptop Computers” and have been further developed by other researchers.

Among them we find Ka-Ping Yee that showed in the CHI 2003 conference his work about “Peephole Displays”. In this interesting article, that has an associated video worth seeing, Yee combines the possibilities of the mobile window to the virtual space with interaction using both hands and the stylus.

PeepHoleCalendar.jpg (128219 bytes) PeepHoleWriting.jpg (64460 bytes)
A virtual calendar seen through a PDA. By moving it horizontally we can explore zones of the calendar that lie beyond the normal limits of of the PDA screen. 
Image as it can be seen in the article by Ka-Ping Yee about Peep-Hole Displays.
Another example of the possibilities of this technology. You can write "outside" the limits of the screen or draw elements much bigger than it by coordinating the movements of both hands.  
Image as it can be seen in the article by Ka-Ping Yee about Peep-Hole Displays.

For this purpose, one hand is used to move the PDA through the virtual 3D space showing its contents while the other hand uses the digital pen to interact with the representation.

For example you can write a longer than the screen text by co-ordinately moving both hands while you write. You can also do large drawings by moving one hand through space and the other on top of the screen. A big circle can be drawn by just holding the pen in the centre of the screen and moving it in circles in space.

Usability studies made by Yee conducted on 25 people using this system show that these techniques are more effective than current ones in order to navigate and browse through large amounts of information in a palmtop computer.

Unfortunately these system require hardware that is not yet miniaturised enough to be used practically. We have to wait, thus, to see these systems in our daily use. The idea, nevertheless, is enormously attractive. 


Links of this issue:

http://www.dgp.toronto.edu/~gf/papers/Chameleon%20-%20Situated%20Info%20Spaces.pdf   Article by G. Fitzmaurice in ACM Communications
http://www.sims.berkeley.edu/~ping/peep/   Article about PeepHole Displays by Ka-Ping Yee in CHI 2003
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