NAME¶
i.maxlik - Classifies the cell spectral reflectances in imagery
data.
Classification is based on the spectral signature information generated by
either i.cluster, i.class, or i.gensig.
KEYWORDS¶
imagery, classification, MLC
SYNOPSIS¶
i.maxlik
i.maxlik help
i.maxlik [-
q]
group=
name subgroup=
name
sigfile=
name class=
name
[
reject=
name] [--
overwrite] [--
verbose]
[--
quiet]
Flags:¶
- -q
-
Run quietly
- --overwrite
-
Allow output files to overwrite existing files
- --verbose
-
Verbose module output
- --quiet
-
Quiet module output
Parameters:¶
- group=name
-
Name of input imagery group
- subgroup=name
-
Name of input imagery subgroup
- sigfile=name
-
Name of file containing signatures
Generated by either i.cluster, i.class, or i.gensig
- class=name
-
Name for raster map holding classification results
- reject=name
-
Name for raster map holding reject threshold results
DESCRIPTION¶
i.maxlik is a maximum-likelihood discriminant analysis classifier. It can
be used to perform the second step in either an unsupervised or a supervised
image classification.
Either image classification methods are performed in two steps. The first step
in an unsupervised image classification is performed by
i.cluster; the
first step in a supervised classification is executed by the GRASS program
i.class. In both cases, the second step in the image
classification procedure is performed by
i.maxlik.
In an unsupervised classification, the maximum-likelihood classifier uses the
cluster means and covariance matrices from the
i.cluster signature file
to determine to which category (spectral class) each cell in the image has the
highest probability of belonging. In a supervised image classification, the
maximum-likelihood classifier uses the region means and covariance matrices
from the spectral signature file generated by
i.class, based on
regions (groups of image pixels) chosen by the user, to determine to which
category each cell in the image has the highest probability of belonging.
In either case, the raster map layer output by
i.maxlik is a classified
image in which each cell has been assigned to a spectral class (i.e., a
category). The spectral classes (categories) can be related to specific land
cover types on the ground.
The program will run non-interactively if the user specifies the names of raster
map layers, i.e., group and subgroup names, seed signature file name, result
classification file name, and any combination of non-required options in the
command line, using the form
i.maxlik[
-q]
group=name subgroup=name
sigfile=name class=name [
reject=name]
where each flag and options have the meanings stated below.
Alternatively, the user can simply type
i.maxlik in the command line
without program arguments. In this case the user will be prompted for the
program parameter settings; the program will run foreground.
OPTIONS¶
Flags:¶
- -q
-
Run quietly, without printing program messages to standard output.
Parameters:¶
- group=name
-
The imagery group contains the subgroup to be classified.
- subgroup=name
-
The subgroup contains image files, which were used to create the signature
file in the program i.cluster, i.class, or i.gensig
to be classified.
- sigfile=name
-
The name of the signatures to be used for the classification. The signature
file contains the cluster and covariance matrices that were calculated by
the GRASS program i.cluster (or the region means and covariance
matrices generated by i.class, if the user runs a supervised
classification). These spectral signatures are what determine the
categories (classes) to which image pixels will be assigned during the
classification process.
- class=name
-
The name of a raster map holds the classification results. This new raster
map layer will contain categories that can be related to land cover
categories on the ground.
- reject=name
-
The optional name of a raster map holds the reject threshold results. This
is the result of a chi square test on each discriminant result at various
threshold levels of confidence to determine at what confidence level each
cell classified (categorized). It is the reject threshold map layer, and
contains one calculated confidence level for each classified cell in the
classified image. One of the possible uses for this map layer is as a
mask, to identify cells in the classified image that have the lowest
probability of being assigned to the correct class.
NOTES¶
The maximum-likelihood classifier assumes that the spectral signatures for each
class (category) in each band file are normally distributed (i.e., Gaussian in
nature). Algorithms, such as
i.cluster,
i.class, or
i.gensig, however, can create signatures that are not valid distributed
(more likely with
i.class). If this occurs,
i.maxlik will reject
them and display a warning message.
This program runs interactively if the user types
i.maxlik only. If the
user types
i.maxlik along with all required options, it will overwrite
the classified raster map without prompting if this map existed.
SEE ALSO¶
The GRASS 4
Image Processing manual
i.class
i.cluster
i.gensig
i.group
AUTHORS¶
Michael Shapiro, U.S.Army Construction Engineering Research Laboratory
Tao Wen, University of Illinois at Urbana-Champaign, Illinois
Last changed: $Date: 2011-11-08 12:29:50 +0100 (Tue, 08 Nov 2011) $
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© 2003-2011 GRASS Development Team