i.gensig.1grass man page

i.gensig — Generates statistics for i.maxlik from raster map.


imagery, classification, supervised classification, Maximum Likelihood Classification, MLC, signatures


i.gensig --help
i.gensig trainingmap=name group=name subgroup=name signaturefile=name  [--help]  [--verbose]  [--quiet]  [--ui]



Print usage summary


Verbose module output


Quiet module output


Force launching GUI dialog


trainingmap=name [required]

Ground truth training map

group=name [required]

Name of input imagery group

subgroup=name [required]

Name of input imagery subgroup

signaturefile=name [required]

Name for output file containing result signatures


i.gensig is a non-interactive method for generating input into i.maxlik. It can be used as the first pass in the GRASS two-pass classification process (instead of i.cluster or g.gui.iclass). It reads a raster map layer, called the training map, which has some of the pixels or regions already classified. i.gensig will then extract spectral signatures from an image based on the classification of the pixels in the training map and make these signatures available to i.maxlik.

The user would then execute the GRASS program i.maxlik to actually create the final classified map.




ground truth training map

This map must be prepared by the user in advance using vector or raster digitizer. Of course other methods could be devised by the user for creating this training map - i.gensig makes no assumption about the origin of this map layer. It simply creates signatures for the classes defined in the training map for the image to be classified (the image is specified in other options - see below). The wxGUI vector digitizer can be used for interactively creating the training map.


imagery group

This is the name of the group that contains the band files which comprise the image to be analyzed. The i.group command is used to construct groups of raster layers which comprise an image.


subgroup containing image files

This names the subgroup within the group that selects a subset of the bands to be analyzed. The i.group command is also used to prepare this subgroup.  The subgroup mechanism allows the user to select a subset of all the band files that form an image.


resultant signature file

This is the resultant signature file (containing the means and covariance matrices) for each class in the training map that is associated with the band files in the subgroup select (see above).

Interactive Mode

If none of the arguments are specified on the command line, i.gensig will interactively prompt for the names of these maps and files.

It should be noted that interactive mode here only means interactive prompting for maps and files. It does not mean visualization of the signatures that result from the process.


The structure of the SIG files generated by i.gensig is as follows (ASCII file, used internally by i.maxlik):
Note: the line numbers are not present in the file but have been added here for explanation only:

SIG file "lsat7_2000_gensig":

 1 #
 2 #water
 3 4186
 4 67.9508 48.7346 37.8915 15.3129 13.8473 12.0855
 5 1.74334
 6 0.439504 2.07267
 7 0.662523 1.63501 4.21189
 8 0.530339 2.40757 5.52857 22.433
 9 0.561184 2.30762 5.18846 20.5364 20.4926
10 0.393218 1.2184 2.63628 9.61528 9.36025 5.85314
  • Line 2: text label
  • Line 3: number of points in class
  • Line 4: mean values per band of the class
  • Line 5-10: (semi)-matrix of band-band covariance

See Also

g.gui.iclass, i.group, i.smap, r.info, r.univar, wxGUI vector digitizer


Michael Shapiro, U.S.Army Construction Engineering Research Laboratory

Last changed: $Date: 2014-11-01 11:11:04 +0100 (Sat, 01 Nov 2014) $

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