Package org.geotools.gce.grassraster

GRASS input/output drivers

In this package the I/O drivers for reading and writing GRASS raster maps are placed.

To better understand the code a good overview should be taken on the GRASS database-Location-Mapset structure, of which a short introduction is given below.

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;
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

The cell header file

A typical grass map header looks like the following:
proj: 1
zone: 13
north: 4928000
south: 4914000
east: 609000
west: 590000
cols: 950
rows: 700
e-w resol: 20
n-s resol: 20
format: 0
compressed: 1

Reclassified files

If the first line reports 'reclass' then this file is a reclassified file and the original data file is given by the following two lines:
reclass
name: soils
mapset: PERMANENT
#1 5 3 8 .... ....

The color table file

Colortables for GRASS 5 and greater are supported.

The format of the color file, which is located in location/mapset/colr/mapname is the following:

The first line is a % character and two numbers indicating the minimum and maximum data values which have colors. Note that in JGrass after the range values we add a third value for alpha support.

After the first line, the list of color rules appears, that can be of the following formats:

  • value1:r:g:b value2:r:g:b interpolation of colors between the two values with the two colors
  • value1:grey value2:grey
  • value1:r:g:b assumption that it means that value1 == value2
  • nv:r:g:b novalues could also have color with such a rule.