Agriculture Reference
In-Depth Information
process very easy to implement. Problems usually begin when interpreting the
outputs.
Vector overlay highlights a more precise areal representation, but it requires
more processing and post-processing to remove sliver polygons. Raster overlay is
more efficient, but it can be less accurate depending on the cell size used in the
analysis. An interested reader can find further details about overlay analysis in
Neteler and Mitasova (
2008
) and in O
'
Sullivan and Unwin (
2010
).
3.4 GRASS: An Open Source GIS
The operations described in the previous sections require GIS software. There are
many GIS software packages available. The most well-known is ArcGIS that is
produced by ESRI.
2
ArcGIS is described by ESRI
s web site as “a complete system
for designing and managing solutions through the application of geographic knowl-
edge. It enables you to perform deep analysis, gain a greater understanding of your
data, and make more informed high-level decisions”. It is commercial software.
In this paragraph we present another GIS software package, GRASS, which is
commonly referred to as the world
'
s leading free GIS software. We have chosen
'
this software because it is free.
Geographic Resources Analysis Support System (GRASS) is a GIS used for data
management, image processing, graphics production, spatial modelling, and visu-
alization for many types of data. It is open source, released under the GNU General
Public License. It can be downloaded from
http://grass.fbk.eu/
. It was originally
developed by the U.S. Army Construction Engineering Research Laboratories
(Champaign, Illinois) (a branch of the US Army Corp of Engineers) as a tool for
land management and environmental planning. In 1997 and 1998 the project was
carried out by the GRASS Research Group of Baylor University, Waco (Texas,
USA). At present, Markus Neteler (Fondazione Edmund Mach, Trento, Italy) is
continuing the development of GRASS into versions 6.4 and 7. The development
team is now international.
GRASS has developed into a powerful package with a wide range of applica-
tions in many different areas of scientific research. GRASS is currently used in
academic and commercial settings around the world, as well as many governmental
agencies. The recent GRASS 6 release introduced a new topological 2D/3D vector
engine and support for vector network analysis. GRASS is developed in the UNIX
(Linux) environment and then transcoded to other systems, among them: UNIX-
like (Solaris, IRIX, Linux, BSD) with a graphical user interface (GUI) in
X-Windows, MS-Windows, MacOS X, and Java (JGRASS).
In this section, we only aim to briefly describe some examples of GRASS
commands for GISs. For more details regarding GRASS and for all the spatial
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