Tjr JT ^Display time
TV T2 Real world time
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Figure 2. Mapping from Real World Time to Display Time
3.3 Combination of Traditional and Dynamic Variables
Barend Kobben and Mustafa Yaman have carried out a
preliminary test for evaluating the perceptual properties of a
series of dynamic visual variables, The test results shows that
the dynamic visual variable moment appears to be not very
useful for cartographic animations unless in combination with
the static visual variable colour and some other variables.
Perhaps the most important conclusion has to be that selection,
which is so important in making cartography a strong tool for
communication, can not be effectively attained by using
dynamic visual variables alone. The traditional variables in
order to accompany dynamic variables are as follows:
The SIZE of an area on a map may be changed to show changes
in value, it represents the size modifications of the objects
during a specified time interval. For example, the sizes of
countries are made proportionally larger or smaller to depict the
amount of oil or coal reserves. An animation can be used to
transform the map of oil reserves into the map of coal reserves
to show the differences in location of the reserves.
SHAPE represents a unique character of each object, sometime
the shape can tell much of the quality of a object. An area on a
map can be made to change in shape. The shape (and size) of
Greenland varies as a result of the influence of a map projection.
An STP can be used to blend between the two shapes to
accentuate the effect of the different projections.
COLOUR is used to concept the calorific properties that
objects to be represented. A color transition of sptio-temporal
objects means from one colour to another during a specified
time interval for a certain number of iterations. The colour
animation can be used to highlight objects of interest on a map.
The blinking of point symbol give a sense of stressing.
OPACITY represents the animation visibility, in other words,
the transparency of the objects from one degree of transparency
to another during a specified time interval. The typical usages
of the opacity animation are blinking to draw attention, fade-in
to make objects progressively appear, and fade-out to make
objects progressively disappear.
DIRECTION represents the direction change of the objects
from a starting angle to an ending angle during a specified time
interval. Objects may be modified with direction change in
terms of a position point. The direction animation is used to
represent the symbols with the obvious arrow or direction.
Another variable DENSITY is often used to represent the
degree of scatter or assemble of spatio-temporal objects, density
became larger if the objects became more collective, whereas it
became smaller when the object scatter sparsely.
By assigning the traditional variables with dynamic variables,
the combination of them become flexible to visualize changing
phenomenon and altering objects. Then a framework is needed
to be created for this combination, which based on the dynamic
symbol base.
4. DYNAMIC VISUALIZATION BASED ON DYNAMIC
SYMBOL BASE
Above we have mentioned many aspects of dynamic symbol,
which is used to visualize the spatio-temporal process, in this
section, the dynamic symbol base is proposed to establish an
strategy for the implementation of dynamic symbol.
The strategy are proposed to define a procedure which can
make a multi-versioned data into a dynamic visualization. First,
the Spatio-temporal association will be used to build a historical
relationship between different spatio-temporal data, then
different Spatio-temporal processes are got and the mapping of
time are derived, based on the dynamic symbol base, temporal
symbol and non-temporal are created by the combination of
dynamic variables and dynamic variables. Thus dynamic
visualization can be displayed by a control over the time-series
dynamic map through a visual interface.
Figure 3 A Framework for Dynamic Visualization Base on
Dynamic Symbol Base
4.1 Spatio-temporal Association
On the basis of the classification of spatio-temporal processed,
adopting a series of algorithms for detecting changes between
different data versions through geometry and thematic
characteristics of spatio-temporal objects, different kinds of
STP will be derived from the association. A time mapping
algorithm will be used to get the relationship between real
world time and display time as well.
4.2 Utilization of Dynamic Symbol Base
Here we propose a dynamic symbol base for the
implementation of dynamic visualization, which provides a
methodology rather than a concrete entity for the application.
Apart from offering a base for the traditional mechanism for
