Originally written by the U.S. Army Construction Engineering Research Laboratories (USACERL) as a tool for land management and environmental planning by the military, GRASS has evolved into a powerful toolkit with a wide range of applications in many different areas of scientific and commercial research. GRASS is currently used in academic and commercial settings around the world, as well as many government agencies (including NASA, NOAA, USDA, the National Park Service, the U.S. Census Bureau, USGS) and many environmental consulting companies.

Raster handling Click to enlarge

Three years ago, CERL stopped developing GRASS. Support, research, and development was assumed by the Center for Advanced Geography and Spatial Research at Baylor University. However, due to the rapid growth and popularity of GRASS, the GRASS Development Team has grown into a multi-national team at numerous locations. In addition to the development headquarters at Baylor University the European headquarters is located at the University of Hannover in Germany. The expanded efforts and coordination has resulted in new GRASS versions, the release of new manuals and documentation, and continued research and development for new versions. It is an exciting time for the GIS community.

The GRASS can be run through either a standardized command line interface or a graphical user interface based on Tcl/Tk. GRASS is also being ported to run under Windows 95/98/NT. There is an internal language that allows users and programmers to create new applications and link GRASS to other software packages. These other applications range from the R statistical language (an open source, no charge clone of the S/S-Plus languages in the Windows world), the PostgreSQL relational data base management system, and numerous hydrological, hydraulic, erosion and pollution models (e.g., SWAT, AGNPS, QUAL2EU).

3D Visualization Click to enlarge

Users can input new data by digitizing from paper sources or on screen, scanning aerial photographs, or reading every type of digital data (raster, vector, point) from a CD-ROM, floppy disk or tape drive. Support platforms include Linux (all processors), Sun Solaris, Silicon Graphics Irix, HP-UX, DEC-Alpha, and Windows95/98/NT. Output can go to printers, plotters or other software programs in a variety of formats.

GRASS accommodates raster, vector and point data. However, all analyses and modeling are done with raster maps. Vector and point data are used for input and output. Utilities permit easy conversion from one format to another.

Because so much data already exists in a variety of digital formats, GRASS has the filters to import and export the most important types. These include DXF, ARC/Info, ARC/View, DLG-3, MapInfo (under development), various satellite image formats, ASCII text and MOSS. Export of raster and vector maps may be to many of the same formats.

Interpolation Click to enlarge

GRASS modules are organized into groups: display, general file functions, imagery (satellite data), miscellaneous, paint, photo (for aerial photographs), postscript (for map printing), raster, shell scripts (macros), sites (point data), vector (for digitizing and making more attractive map products) and 3D visualization (including "fly-through" animations).

GRASS allows users to analyze, store, update, model, and display data quickly and easily. Although it was originally developed for use in land planning, its capabilities have been expanded and used in the fields of ecology, environmental science, engineering, hydrology, geology, physics, statistics, remote sensing, business and many others.

Elevation Modeling Click to enlarge

GRASS comes fully equipped (no batteries needed):

• expert system engine (r.infer)
• a powerful module for delineating watersheds and sub-basins from digital elevation models (r.watershed), hydrology (r.cn) and erosion potential models (r.answers) and finite element analyses (r.water.fea)
• viewshed and line-of-sight analyses (r.view and r.los, respectively)
• transect (r.transect)
• landscape ecology analyses (r.le)
• a module which permits you to enter any analytic equation you need for map algebra (r.mapcalc)
• neighborhood analyses (r.neighbors) and cost analyses (r.cost)

The Surface Water Assessment Tool (SWAT) has an integrating linkage which permits this basin-scale model to run complex hydrologic and channel transport simulations and models. Scales can be from a small parcel to the entire United States. Basically, if there is an analytic equation or solution defined for your needs, GRASS will allow you to use it on your spatial data.

What does GRASS offer that the commercial products don't? The major advantage is value. You can get the complete GRASS for no cost, or just the cost of distribution. And, you get all the source code with it. You are free to modify the code to suit your needs, add capabilities by writing (and contributing, if you want to) new modules and fixing bugs. Based on estimates from downloads at the headquarters sites and the mirrors, there are approximately 40,000-45,000 users world wide. Of course, that does not include others who obtained the system without directly downloading it. The Windows port is well under way while the UNIX versions are fully available now. For more information about GRASS, visit the web sites. You can start by pointing your browser to http://www.baylor.edu/~grass.