Geography Reference
In-Depth Information
horizontal and we describe in Fig. 3b the geometry by a simple plan {(x, y), z0}. An
area represents values included in a range of pollution between an area-min-value
and area-max-value . The area is mapped in a specific colour that belongs to the
colour-family of the view .
A 3D-V-Grid object is a Visual object (V for Visual) that is a 3D grid. It is
defined in fourth section.
Statistics and 3D Visual Grids to Map Phenomena Such As
Pollution
Several studies are proposing solutions to map pollution thanks to GIS (ESRI 2007 )
or (Al Koas 2010 ). One of the key points is to be able to analyze the data in order to
detect critical zones or specific events by means of appropriate methods. Rude and
Beard ( 2012 ) explore the detection of high-level events from spatially distributed
time series. Their goal is to extract interesting occurrences from time series as
aggregate patterns of primitive patterns. Peuquet ( 2012 ) proposes a statistical
temporal pattern discovery technique called T-pattern analysis via a prototype
called Stempo. So, we need methods to make spatio-temporal analysis on 3D grid
data. The first conclusion is then that it is not possible to master the representation
of phenomena without solid spatio-temporal analytical tools (such as R).
In terms of graphical representation, in third section, we project the 3D infor-
mation in 2D. 2D is convenient as most of today tools (including web services) are
dealing with 2D data. However phenomena varies in Z and this information is
important as space is not lived in the same way for all altitude. Pollution at 50 cm
height has obviously not the same impact as at 1.50, 4 or 20 m.
In order to perceive this variation of values according to z, a possibility is at least
to view the topographic data in 3D as illustrated in Fig. 4 . In this Fig. 4 both left
images are not GIS but image viewers. Pollution is perceived as a plan grid but at
least a 3D view allows seeing at which altitude the pollution is computed and
mapped.
Fig. 4 3D representations of pollution on different tools
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