GRASS GIS (Geographic Resources Analysis Support System) is an open source, Free Software Geographical Information System (GIS) with raster, topological vector, image processing, and graphics production functionality that operates on various platforms through a graphical user interface (GUI) or command line interface (CLI). It is released under GNU General Public License (GPL).

This manual introduces the reader to the Geographic Resources Analysis Support System from the programming perspective. Design theory, system support libraries, system maintenance, and system enhancement are all presented. Standard GRASS 4.x conventions are still used in much of the code. This work is part of ongoing research being performed by the GRASS Development Team, an international team of programmers, GRASS module authors are cited within their module's source code and the contributed manual pages.

An up-to-date version of this Programmer's Manual is available at http://grass.osgeo.org/programming7/

© 2000-2015 GRASS Development Team
Published under GNU Free Documentation License (GFDL) http://www.fsf.org/copyleft/fdl.html

This manual comes with ABSOLUTELY NO WARRANTY. The development of GRASS software and this manual is kindly supported by the Open Source Geospatial Foundation, who provides the GRASS main infrastructure.

Main web site: http://grass.osgeo.org

Principal library

(the name refers to the directory name in lib/ in the source code)

gis: GRASS GIS Library, with following subsection
- Raster File Processing
- Vector File Processing
- Sites File Processing (legacy, merged into Vector File Processing)

Further libraries

(the name refers to the directory name in lib/ in the source code)

arraystats: Library of statistics for arrays of doubles - arraystats (new, under development)
bitmap: Bitmap library for X Window Bitmaps - bitmap
btree: Binary tree library - btree
cairodriver: Cairo display driver library - cairodriver
cdhc: Library for testing normality and exponentiality - cdhc
cluster: Library for cluster analysis (image processing) - cluster
datetime: DateTime library - datetime
db: GRASS DBMI DataBase Management Interface
display: GRASS Display Library
driver: Graphics monitor driver
dspf: DSPF libary - dspf (obsolete?)
edit: Raster edit library (cellhd, history, cats) - edit
external: External libraries from other projects (such as shapelib or bwidget) - external
fonts: Hershey library - fonts
form: TCL/TK forms library - form (obsolete?)
g3d: GRASS Grid3D raster volume Library
gmath: GRASS Numerical math interface (generic mathematical functions and BLAS/LAPACK library wrapper)
gpde: GRASS partial differential equations Library (GPDE) (partial differential equations library)
gtcltk: Tcl/Tk stuff - gtcltk
imagery: GRASS Imagery Library
init: Library Initialization (GRASS initialization code + scripts)
linkm: Linked list memory manager - linkm (obsolete?)
ogsf: GRASS openGL gsurf OGSF Library (OpenGL (R) ported gsurf library (required for NVIZ))
pngdriver: PNG display driver library - pngdriver
proj: GRASS and the PROJ4 projection library (wrapper to PROJ4 projection library)
psdriver: PostScript display driver library - psdriver
python: GRASS Python Scripting Library
raster: GRASS Raster Graphics Library (note: raster map functions are in GRASS GIS Library)
rowio: Raster row in/out library - rowio
rst: Library for interpolation with regularized splines with tension - rst
segment: GRASS Segment Library (segment library for segmented raster reading)
sites: Old Sites library, now interfaced to GRASS 6 Vector Architecture - sites
stats: Raster stats library - stats
symbol: Drawing symbols for point vector data library - symbol
vask: Cursor management library - vask
vector: GRASS 6 Vector Architecture (GRASS Vector and Direct Graph Library)
- vedit: GRASS Vedit Library - vector editing
- neta: GRASS Network Analysis Library
nviz: GRASS Nviz Library (used by wxGUI Nviz extension and CLI-based Nviz module)

Interfaces

GRASS Python Scripting Library

GUI

GRASS wxPython-based GUI

File structure of GRASS Location

A GRASS raster map consists of several files in several subdirectories in a mapset, organized as follows:

cellhd/: map header including projection code, coordinates representing the spatial extent of the raster map, number of rows and columns, resolution, and information about map compression;
cell/, fcell/ or grid3/: generic matrix of values in a compressed, portable format which depends on the raster data type (integer, floating point or 3D grid);
hist/: history file which contains metadata such as the data source, the command that was used to generate the raster map, or other information provided by the user;
cats/: optional category file which contains text or numeric labels assigned to the raster map categories;
colr/: optional color table;
cell_misc/: optional timestamp, range of values, quantization rules (for floating point maps) and null (no-data) files;

A GRASS vector maps are stored in several separate files in a single directory. While the attributes are stored in either a DBF file, a SQLite file or in an external DBMS (PostgreSQL, MySQL, ODBC), the geometric data are saved as follows:

head: vector map ASCII header with information about the map creation (date and name), its scale and threshold;
coor: binary geometry file which includes the coordinates of graphic elements (primitives) that define the vector feature;
topo: binary topology file describes the spatial relationships between the map's graphic elements;
hist: history ASCII file with complete commands that were used to create the vector map, as well as the name and date/time of the map creation;
cidx: binary category index file which is used to link the vector object IDs to the attribute table rows;
dbln: ASCII file which contains definition(s) of link to attribute storage in database (DBMS).

Diagram of GRASS file structure

Table of contents

Principal library

Further libraries

Interfaces

GUI

File structure of GRASS Location