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In-Depth Information
virtual space is represented in the center of the time bar. There are some small
triangles on the left side of the time bar. The triangles represent the time of spatio-
temporal objects, that is, cameras as points in the time axis. Thus, the virtual
space is a visualization of spatial attributes of spatio-temporal objects, while the
time bar is a visualization of temporal attributes of spatio-temporal objects. A
user can change the present time and the present time interval of the time bar.
Changing the present time realizes time walk-through, and corresponds to changing
the viewpoint or walking through a virtual space. Changing the present time interval
may correspond to changing the field of view in the virtual space. There is another
interpretation that extending the present time interval means going backward while
keeping the central point fixed in the virtual space for extending the view. Thus,
changing the present time interval is related to changing the scale of time. We can
also select the mode for LoD from the selections: Spatial LoD (S-LoD), Temporal
LoD (T-LoD) and Spatio-Temporal LoD (ST-LoD). The three kinds of LoD are
defined by different definitions of the distance: 3D distance, time distance and 4D
distance. Figure 13 shows changing the present time, that is, going back to a 2
hours past virtual space. Yellow arrows are changed into red arrows because they
exist in the future from the present time, interval. Extending the present time
interval increases the number of objects in the view, all objects become yellow.
Shortening the present time interval decreases the number of objects. Figure 14
shows changing the LoD mode into Temporal LoD.
7
Conclusions
Spatial sensors are expected to be affordable and become precise enough to generate
spatial description data for objects in the real world in the near future. The spatial
description data of a video camera's condition measured by the spatial sensors are
also useful for browsing and retrieving video data spatially. The spatial data of the
video camera provide richer visual index environment. We can retrieve both pictures
and videos in 3D virtual spaces as well as on 2D maps. Also, real-time 3D computer
graphics hardware enables us to walk through a 3D virtual space and to appreciate
videos replayed in the 3D virtual space. This kind of environment can provide
users with spatially browsing of videos in a virtual space. We can experience virtual
spaces in more realistic ways because real world videos can be replayed in a virtual
space. While we walk though 3D virtual spaces which have their corresponding
existent real world spaces, we can be aware of the existence of videos in t he
virtual spaces because there are 3D icons for video sequences, and can appreciate
replaying videos more spatially and naturally in the virtual spaces. This application
promises to manage video data for certain application domains, such as sightseeing
tours of the real world, simulations of the real world, and virtual disaster
management systems.
This paper has presented a concept
Time walk-through
by means of introducing
time extension to the ordinary LoD. This framework is significant for browsing
