We need a visualization model that is understandable by the biologists---the users of the system. The addition of the time axis is useful because of its familiarity.
There was an initial bias to map only temporal variables such as entry date or evolutionary distance to the time axis. There may also be a tendency not to map the temporal variables to a spatial axis. In AlignmentViewer, these restrictions are removed so any variable can be mapped onto the time axis or a spatial axis. Thus, a variable may have spatial or temporal quality, but we are not restricted to represent them in a certain way on the screen. So, for example, score can be mapped onto the time axis.
To control the time axis, AV uses the VCR-like control panel shown in Figure 3. This provides a familiar, easy to use interface controlling a number of different capabilities. The buttons near the bottom control the high cutoff slider with reverse, pause, forward play, and loop capability. The entry box to the right of these buttons specifies the stepsize between successive frames. In Figure 3, when a user presses the forward play button, the high cutoff slider increases by 20 each frame. We called this `` Accumulative Play,'' as the results accumulate on the screen as the high cutoff increases. Reverse accumulative play and looping are also possible.
Figure 3: Time axis animation controls
The buttons flanking the sliders are more complex. The smaller buttons control forward play and reverse play on the respective sliders. So there are actually two buttons that both do forward play. The two buttons are aliased to the same function because first-time users could understand the VCR-like buttons more easily. The bigger buttons that straddle the two sliders provide `` Sliced Play''. Pressing the forward sliced play button increases the high and low cutoffs simultaneously. Thus, the user is presented with ``slices'' of the data with respect to the time axis.
Initially our design did not allow variables to be doubly mapped onto two different axes. We found that this was actually a limitation, and thus the system allows mapping the same variable to two different axes. As an example where this might be useful, if the same variable was mapped to the X axis as well as the time axis, the user could then view successive slices of the data along the X axis using the animation controls.
Ed H. Chi
Thu Jul 11 10:52:57 CDT 1996
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