Friday, February 15, 2008

Docs: theJGrass workspace

Overview of a GRASS database structure:

Most important files and folders for now
  • WIND - contains the active processing region and the resolution
  • PROJ_INFO - contains the information about the projection
  • PROJ_UNITS - contains the information about projection units used
  • cell, fcell - contain the raster files
  • vector - contain the vector data since GRASS 6
  • sites_list - contain the sites type data, deprecated from GRASS 6 on, but maintained in JGrass

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;

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).

Taken from the GRASS developer's manual

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