Download Interpreting Communication Data Sets by using a Multiple View

Interpreting Communication Data Sets by using
a Multiple View Virtual Environment
ANDRE HINKENJANN
GMD- The German National Research Center for Information Technology,
Schloß Birlinghoven, St. Augustin, Germany
[email protected]
Abstract. We present a multiple view system that allows the user to explore communication data sets. The
system is implemented using virtual environment techniques. It utilizes the two-sided Responsive
Workbench, an L-shaped stereo projection table. An intuitive user interface is available through the use of the
Cubic Mouse, an interaction device developed at GMD. The user can switch between three views of a radio
communication data set and gain information about displacement of transmitters, communication patterns and
hierarchical structure of the transmitter net. With each view the user can select several tools to interpret the
data set, like text and audio drilldown tools.
1 Introduction
In this paper we present our approach to visualize and interpret point-to-point radio
communication with the help of different views of the data set. The system accepts data as
ASCII text files which contain lines of the following parameters: date/time, sender name,
receiver name, type of communication (data/speech), and a pointer to audio files. This data
could also be captured as snapshots from a system that delivers this information live. For
the transmitter names there exists an additional file containing a mapping from names to the
Gauß-Krüger coordinates (the German surveying offices’ geo-coordinate format) of the
transmitters and to additional textual information.
The system is designed as a virtual environment using VR technology like the twosided Responsive Workbench (Krüger et al. [1]) and interaction devices such as 6-degreeof-freedom pointers and the Cubic Mouse, a special device explained later on. The user
wears active LCD shutter glasses to be able to see the data set in stereo (Figure 1). Attached
to the glasses is a tracking sensor that enables the graphics computer to render a stereo
projection for the user’s point of view.
For the exploration and interpretation of data sets it is often helpful to change views of
the data set, especially if we want to extract different kinds of information. Because of that,
we implemented our system as a multiple view system. According to Baldonado et al. [2], a
single view of a conceptual entity is a set of data plus a specification of how to display that
data visually. Views are defined to be distinct if they allow the user to learn about different
aspects of the conceptual entity. A multiple view system uses two or more such distinct
views to support the investigation of a given conceptual entity.
Each of the three views our system offers is a accompanied by a set of tailored tools for
visual and “sonic” data mining. To be able to extract persistent information, tools like
markers and a report writer are available which store the information in text files.
The following sections of the paper describe the three available views in more detail.
Figure 1: A user standing at the
Responsive Workbench using the system.
2 3-D terrain view
With the aid of this view, the user is able to derive an overview of the spatial displacement
of transmitters, to extract information out of transmitters and communications and to add
persistent information to the data set.
In 3-D terrain view the additional file that describes the coordinates of transmitters is
evaluated and the transmitters are placed in the terrain surrounding their coordinates. To
visualize the terrain, we used data from Landesvermessungsamt Bonn (a German public
surveying office). This data is made up of two parts: A regular height grid with a resolution
of 50 by 50 meters and a height accuracy of 5 meters. From that we build triangle strips to
optimize render performance. The second part is high-resolution photographs of the terrain.
This data is resampled to fit into the texture memory of an sgi ONYX2 IR2 that has a
limitation of 64MB of texture memory. We currently do not use level of detail or detail
textures, because a medium resolution of textures is sufficient for an overview of where the
transmitters are placed. This is an option for future work, when larger terrains will be
explored. Textures are mapped to the triangulated height data and output to the Workbench
as a three-dimensional model of the terrain surrounding the transmitter locations.
The user of spatial mode is presented with the following subdivision of the rendering
area:
•
Top left: This part of the screen is reserved for a user-selectable time interval mode.
With this mode the user selects to see communication relations at a specific time,
before a specific time, after a specific time or within a specific time span.
•
Top middle: This area shows the time slider that is used to select the time. Below
that the time scale is printed in text form. When the user selects to see all
transmissions in a certain interval of time, another time slider is added to the top
middle section of the screen.
•
Top right: This area contains user-selectable tools in each of the three views,
although the amount and types of tools may vary from view to view. The tools are
represented as 3-D icons in front of sockets. Textual information about the currently
selected tools is presented directly above the icons after selection.
The rest of the rendering area is available for the visual representation of the data set.
Figure 2: 3-D terrain view screen partitioning
Figure 2 shows the complete vertical screen of the Workbench in 3-D terrain mode
(Only the vertical projection screen is shown in the figures of this paper although the
horizontal projection area of the two-sided Responsive Workbench is also used for a
continuous three-dimensional illustration of the data set). The transmissions are indicated as
small lines connecting the respective senders and receivers. In figure 2, time mode is “after
a specific time” and the time slider is positioned at the beginning of the time line, so the
complete net is shown. A color code is used to distinguish data from speech
communication.
The following tools are available to the user in 3-D terrain mode:
•
Audio drilldown - this enables the user to hear the content of the transmissions she
selects. When this option is selected the user can use the pointer to click on a line
representing a communication. This triggers a playback of the audio content of that
communication.
•
Transmitter inspection - allows the user to jump to the position of the selected
transmitter to get a view from that location
•
Report writing - to add persistency to the system the user is able to click on the
report icon to write a report about his findings. This report is shown as text in the
virtual environment and in addition it is saved in a text file.
•
Text drilldown – after activating this tool, the user can select an arbitrary
transmitter and is given textual information by a small label next to the transmitter
(Figure 3).
Figure 3: text drilldown
•
Radio wave distribution - radio wave distribution showing the field strength
around a selected transmitter (this is currently simulated) (Figure 4).
Figure 4: radio wave distribution
•
Transmitter marking - this is a tool that can be used to mark a selectable
transmitter. This mark can be interpreted e.g. to show that this sender belongs to a
certain hierarchy level. This can be used to add linking from this view to
hierarchical view (Figure 5).
Figure 5: transmitter marking
3 3-D matrix view
This view of the communications is especially useful for recognizing clusters of
communication activity because it shows all of the communications at once. In addition,
communication patterns like question and answer series (request/acknowledge) are quickly
recognizable. This view does not show the spatial relationship of the transmitters. In
contrast to 3-D terrain view, 3-D matrix view shows a three-dimensional plot of senders
and receivers in a 3D Cartesian coordinate system. The x-axis is labelled senders, the y-axis
receivers and the z-axis is labelled time. A cube is shown at coordinates (A,B,T) whenever
a sender A is communicating with a receiver B at time T. The size and colour of the cube
reflect two additional parameters such as the type of communication (data/speech), the
accumulated duration of the communication at T or the “importance” of the transmission.
3-D matrix view utilizes a special interaction device, developed at GMD, called the
Cubic Mouse (Figure 6).
The Cubic Mouse [4] is a 3-D input device based on the concept of props. It consists of
a cube-shaped box with three perpendicular rods passing through its center. We use a sixdegree-of-freedom (6-DOF) tracker embedded in the Cubic Mouse to track the device’s
position and orientation. The rods can be pushed and pulled, allowing the constrained input
of three degrees of freedom. In addition, the Cubic Mouse has six applicationprogrammable control buttons mounted on one face and single buttons at both ends of each
rod.
Figure 6: The Cubic Mouse
We use the Cubic Mouse as a prop representing the whole data set. As the user moves
or rotates the cubic mouse, the 3-D plot of the data set is moved and rotated according to
that. The rods of the Cubic Mouse move three semi transparent virtual clipping planes that
are oriented perpendicular to the coordinate axes. By sliding the rods back and forth, the
user can clip away parts of the data set corresponding to the clip axis. For example, by
moving the z-axis rod, the user can clip away all parts of the data set that represents
communications before or after the selected time, depending on the rod position. The
buttons at the end of the rods switch the clip orientation. This way, the user can fix a certain
sender, to see what receivers it communicated with over time.
Figure 7: Fixing a receiver
When the receiver is fixed by positioning the clipping plane, all senders
communicating with that receiver over time show up (Figure 7).
Fixing a certain time reveals what senders and receivers communicated at that time.
All axes and clip planes are color coded for ease of use. As with 3-D terrain mode, the user
can use tools to explore the data set, like audio/text drilldown by clicking on a cube or
adding persistent information by writing a report.
4 3-D hierarchy view
After a user has interpreted the data set by use of spatial mode and abstract mode and after
assigning hierarchy/importance levels to transmitters by transmitter marking, she now has
the possibility to explore the organizational structure of the participating communicators
(the structural information might also be pre-stored in an additional database).
As an example, a tree-like view is presented that shows the hierarchy of communicators
(Figure 8). The system is not limited to trees, but can also display forests. The root of the
example tree represents to top of the hierarchy; the leaves represent the lowest level of the
hierarchy. Two transmissions are shown as additional lines (with different colors than
hierarchy connections) that connect transmitters. This is to show the impact of a future
addition of a time slider, like in the spatial view.
The Cubic Mouse is again used to clip away portions of the data set. Here, the
horizontal clipping plane is clipping the hierarchy levels (like in figure 8) while the two
other clipping planes can be used to clip away parts orthogonal to that, e.g. a complete
subnet of the communication network. Again, tools, like text/audio drilldown tools, from
the top right area of the projection can be applied by the user.
Figure 8: 3-D hierarchy view of the communicators
5 Conclusion and future work
We presented a system to explore data sets of point-to-point radio communication. The
system offers three different views of the data set that are each accompanied with a set of
tailored tools. Each of the views are used to extract different types of information “hidden”
in the data set, like spatial displacement of transmitters, communication patterns,
communication clusters and hierarchical information.
Besides adding more functionality to the views and adding more views, future work
will include level of detail for terrain rendering and data filtering when larger data sets and
larger terrains are to be explored.
Although 3-D terrain view offers tools for selecting times or time intervals, the other
tools do not. This extension is currently under development. In addition there currently
exists only limited linked brushing. When the user marks transmitters in terrain mode as
belonging to a certain hierarchical level, the 3-D hierarchical mode reflects that as a height
in the hierarchy tree. Marking it in all views simultaneously is currently being
implemented.
The hierarchy of communicators is rendered as a three-dimensional node and link
diagram. The number of transmitters that can be shown simultaneously is somewhat limited
by this type of diagram. We would like to evaluate other tree-maps, like 2D space-filling
approaches [5] or cushion tree-maps [6]. With these maps, the 2D area corresponds to a
scalar value that is added to each node. In a VE, we can add a second value as a height
value for each 2D region that corresponds to a node of the hierarchy.
Although we did not implement concurrent multiple views because of the geometrical
complexity of parallel views (limited by the performance of the rendering system) we
would like use parallel views with limited complexity. This might allow the user to directly
compare views and may help in reaching the defined goals more efficiently.
6 Acknowledgement
This work was funded by Medav GmbH, Germany. We wish to thank Medav for fruitful
discussions and suggestions for the views and for the provision of the communication data
sets. We would like to thank Jeremy Eccles for designing icons for the user interface and
Stefan Ritter for many valuable hints to improve the system.
References
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[3]
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on
Treemaps:
Information