6 GRASS basics: command structure and user interface

GRASS is a complete, hybrid, modularly-structured GIS with raster and vector functions. Each GIS function is managed by its own module. Thus, the system is clearly structured and appears transparent. Another advantage of this modularity is that only necessary modules are executed, which preserves system resources.

**Figure 2:** GRASS GIS manager with Spearfish dataset
$\includegraphics[width=0.75\textwidth]{finalpix/display_manager.eps}$

**Figure 3:** GRASS NVIZ viewer with satellite data
$\includegraphics[width=0.75\textwidth]{finalpix/nviz_satellite.eps}$

Currently three graphical user interfaces (GUI) are available in addition to the traditional command line. The default GUI is the GIS manager. The map viewer NVIZ includes support for raster, vector, volume display, animations, profiles and more (see figures 2 and 3).

**Figure 4:** QGIS geodata viewer with GRASS interface
$\includegraphics[width=0.75\textwidth]{finalpix/qgis07_map_composer.eps}$

An external project, the user-friendly geodata viewer QGIS, provides direct support for GRASS. From QGIS version 0.7 onwards an extensive GRASS interface with on screen digitizer and GIS functionality is included. Also included is a new map composer tool for paper map production (see figure 4).

**Figure 5:** JAVAGRASS interface
$\includegraphics[width=0.75\textwidth]{finalpix/javagrass_spearfish.eps}$

Finally, there is JAVAGRASS (JGRASS), which is a multi-platform, multi-session GRASS framework (see figure 5). JGRASS packages GRASS to be used in production environments as opposed to research environments. The architecture of JGRASS follows a client-server model internally, separating the Graphical User Interface (GUI) from the spatial processing engine. This separation allows the easy development of remote access capabilities.

**Table 1:** GRASS Command Overview
GRASS Command Overview
prefix	function class	type of command	example
d.*	display	graphical output	d.rast: views raster map
			d.vect: views vector map
db.*	database	database management	db.select: selects value(s) from table
g.*	general	general file operations	g.rename: renames map
i.*	imagery	image processing	i.smap: image classifier
ps.*	postscript	map creation format	ps.map: map creation
		in Postscript
r.*	raster	raster data processing	r.buffer: buffer around raster features
			r.mapcalc: map algebra
r3.*	voxel	raster voxel data processing	r3.mapcalc: volume map algebra
v.*	vector	vector data processing	v.overlay: vector map intersections