Geography Reference
In-Depth Information
Contrast
Contrast is the antithesis of assimilation and may be described as the accentuation of dif-
ferences. These two terms indicate how our brain, taking only a subset of the information,
assumes similarity or difference until there is enough visual evidence to the contrary. By
placing a dividing barrier into the same illustration as the one shown in Figure 11.7, the two
halves now look distinctly different, but in fact they have internally the same
assimilation
tendency as the whole (Figure 11.8).
Negative and positive
Artists define the figure as positive space and the ground as negative space. Negative space
surrounds positive space and appears to extend continuously behind the figure. Although,
it has less importance, it is usually larger in size. Positive space appears more clearly defined.
A line or a contour is by definition a very positive feature. The white stripes in the Figure
11.9 illustration definitely appear to be there, but in reality are just an illusion.
The human visual system is a wonderful structure built on evolution, but due to limits in
information flow, there are times when it fails. We need to know when and how these failures
can affect visualizations. Presenting data is a balance from creating the most appropriate
visual experience, and avoiding the pitfalls of visual illusions, to finally create a meaningful
geographic representation.
An important part of this equation is the physical space, which the viewer is enclosed
in while observing the visualization. This needs to provide both a stereoscopic and a wide
viewing angle display. We will consider next just a small selection of visualization centres
that have aimed at presenting data at the correct resolution and colour balance, but also try
to understand how the user will experience and interact with the visualization.
11.3 Constructing large-scale visualization systems
There are a number of specialized stereoscopic enabled visualization centres used by earth
scientists and other researchers for geographic representations in the UK (this includes all
of the oil companies, as well as the British Geological Survey). These try to increase the level
of presence with all the visual cues, and to avoid issues associated with confusing the human
visual system. We also illustrate various modes in which these centres have been used.
In 1999 Manchester Visualization Centre constructed one of the first large-scale scientific
visualization spaces in the UK, consisting of an active stereo 7 m curved wall similar to a flight
simulator (Figure 11.10). This allowed scientific users to achieve a higher understanding of
their data, but its cost, including building work, was over £1 million, which meant only a few
institutions could afford to build such a centre for their research. Figure 11.10 shows views
of different earth scientists exploring a three-dimensional geological data field consisting
of underground surface levels of rock, as well as a volume of ultrasound readings. The user
operates on her own, viewing the data through active stereoscopic glasses, providing near
perfect three-dimensional vision as the system tracks both her head and the interactive wand
in her right hand. This enables the intuitive exploration in three dimensions of this large data
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