GRASS GIS Geographic Resources Analysis Support System Kurt Menke, GISP
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.
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
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
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.)
Examples 3D Visualization
Vector Analysis…GRASS isn’t just for rasters anymore Buffers Charts Networks
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
GRASS Database Simply a folder where GRASS LOCATIONS and MAPSETS are stored
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
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.
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.
GRASS Database LOCATION MAPSETS
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.
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.
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).
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.
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.
Resources Documentation - Manuals http://grass.osgeo.org/wiki/GRASS_Documents Listserv http://lists.osgeo.org/mailman/listinfo/grass-user Wiki http://grass.osgeo.org/wiki/Main_Page
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