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yellow as their colors. The colors of objects which are behind the present time are
blue, and the colors of those which is ahead of the present time are red. Users can
find out the rough time of spatial objects from their color. If a user moves to the
advancing time, the blue objects would change into yellow and red successively.
Also, if a user changes the time interval into a longer one, the number of objects
existing in the time interval increases and the colors of the objects change according
to the ratio of the time of each spatial object to the present time interval.
Figure 12: Time bar with a virtual space
(Present time, Present interval)=(13:00, 4:00)
6.5
Prototype System “TimeWalk”
We implemented a prototype system called
Time Walk
to realize the time extension
to LoD. We used an O2 workstation of SGI (Silicon Graphics Inc.) and SGI IRIS
Performer 2.0 graphics library for prototyping. Our experimental spatio-temporal
data are the movements of video cameras. The multiple representations of the
spatio-temporal objects are a point, an arrow and multiple arrows for LoD. There
are three modes of LoD for our prototype system: S-LoD (LoD by Space scale
distance), T-LoD (LoD by Time scale distance) and ST-LoD (LoD by Spatio-
Temporal scale distance).
We explain the user interface of the prototype system using Figure 12. The 3D
arrow icons represent the movements of the camera. There is the bar called
time
bar
in the left side of the display screen. The time bar represents the present time
interval when all visible 3D arrow icons exist. In this example, the time bar
represents 4 hours, that is, from 11:00 to 15:00. The present time 13:00 of the
