Kurt Menke, GISP

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GRASS GIS Geographic Resources Analysis Support
System
Kurt Menke, GISP
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GRASS GIS
What is it? A robust Open Source GIS that runs
on a wide variety of computer platforms including
Windows, Linux, and Macintosh OS X.
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GRASS Factoids Originally developed by the
U.S. Army Construction Engineering Research
Laboratories (USA-CERL) between 1982 and 1995
Open Sourced in 1997 Over 1 million lines of
code, developed by an international team of
contributing programmers and organizations.
Over 350 geoprocessing functions Currently at
version 6.4.1
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• GRASS Evolution
• GRASS has evolved greatly over the last several
  years
• Historically only available for LINUX
• It's only with version 6 that it's been
  available to Windows users
• Like ArcInfo it was originally purely
  commandline software
• Part of the move to Windows has been the
  development of a GUI graphical user interface
• The full power of the package is still reserved
  for commandline users

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• GRASS Evolution

• Has a different vocabulary and workflow which
  takes getting used to
• Is very modular
• Consisits of many commands
• This allows for automation of geoprocessing
  through standard scripting languages (shell
  scripts, python, perl, etc.)

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Examples - Cartography
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Examples 3D Visualization
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Examples - Image Processing
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Vector AnalysisGRASS isnt just for rasters
anymore
Buffers
Charts
Networks
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• GRASS Databases, LOCATIONs and MAPSETs?
• These are the foundation of data organization in
  GRASS
• These cause the most confusion to beginners
• Must be set up before you begin working
• Essentially a hierarchy of folders

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GRASS Database Simply a folder where GRASS
LOCATIONS and MAPSETS are stored
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• LOCATIONs
• LOCATIONs
• Simply folders
• Represent a geographic extent of interest
• Contains data sets that should all be in the same
  coordinate system!
• Every LOCATION has a PERMANENT directory which
  stores some basic information about the whole
  LOCATION
• PERMANENT can be a good place to store base files
• You can think of a LOCATION as a data library for
  a region of interest
• Almost like a geodatabase

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• MAPSETs
• MAPSETS
• Technically they are subfolders under any
  LOCATION.
• For example, PERMANENT is a MAPSET
• Conceptually similar to Feature Datasets
• They are workspaces in which you can organize
  GIS data thematically, geographically, by project
  or by user.
• Every GRASS session runs under the name of a
  MAPSET.
• A MAPSET may be a geographical subset or as
  large as the parent LOCATION.

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MAPSETs cont. MAPSETS cont In a networked
environment with several users working within the
same LOCATION, MAPSETS can play a special role.
Can be set up so that users may only select
(and thus modify) a MAPSET that they own (i.e.,
have created). However, data in all MAPSETS for a
given LOCATION can be read by anyone (unless
prevented by file permissions). The
"PERMANENT" MAPSET typically contains the
read-only base maps like the elevation model,
while the other LOCATIONs are readable and
writable by their owners. The "PERMANENT"
MAPSET also contains some information about the
LOCATION itself that is not found in other
MAPSETS (projection info etc.), thus it must
exist in every LOCATION.
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GRASS Database LOCATION MAPSETS
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RUNNING GRASS When first running GRASS, you have
to identify a GRASS GIS Database folder The you
have to define or load a LOCATION It contains the
data as well as projection definitions If
starting from scratch on a new project You need
to identify a folder as your GRASS Database Then
you must create a folder for your LOCATION, i.e.
My_Project Define the spatial reference for data
in that LOCATION as well as the spatial extent.
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RUNNING GRASS
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GRASS DATA GRASS requires that all data be
imported into a GRASS database. It can read and
import a wide variety of datasets via
GDAL/OGR. Data is stored as GRASS vectors and
GRASS rasters which are themselves file
formats. If starting a new project - once
you've established your Database, LOCATIONS and
MAPSETS - you need to import your data. You'll
do that in Lab 5.
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GRASS REGIONS Like an environmental setting in
ArcGIS The region defines the geographic area in
which GRASS should work. It is characterized by
several parameters - Spatial reference (e.g.
UTM, latitude-longitude, etc) - Spatial extent,
i.e. the North/South/East/West limits of the
area covered - The number of columns and
number of rows for the data - Resolution, i.e.
the spatial extent divided by the number of
rows (N-S resolution), columns (E-W resolution).
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GRASS REGIONS The default values of these
parameters for a given LOCATION are stored in the
DEFAULT_WIND file in the PERMANENT MAPSET of that
LOCATION.
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GRASS REGIONs Why do we care about the REGIONs?
Display if the REGION is set to a smaller
extent than the data you're working with, the
display command will only show the portion of the
map that is within the REGION. Export the data
export commands will work within the REGION
Analysis and Resolution will be effected by
REGION settings. REGIONS are how you control
raster resolution. Ideally, the default REGION
of a LOCATION should encompass the entire area
covered by all the maps in that LOCATION.
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Resources
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Resources
Documentation - Manuals http//grass.osgeo.org/wik
i/GRASS_Documents Listserv http//lists.osgeo.org
/mailman/listinfo/grass-user Wiki http//grass.os
geo.org/wiki/Main_Page
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Lab 4 Intro to GRASS GIS Using wxPython
GUI there is one other GUI...tck/tk Plus a
commandline text interface wxPython is a GUI
toolkit for the Python programming language.
This is what the GUI is written in...thus the
name You'll learn how to start GRASS and do some
basic things