i.svm.train - GRASS manual
Author: GRASS Development Team
Description: i.svm.train: Train a Support Vector Machine
Keywords: imagery, svm, classification, training

## NAME

i.svm.train - Train a SVM
Train a Support Vector Machine

## KEYWORDS

imagery, svm, classification, training

## SYNOPSIS

i.svm.train
i.svm.train --help
i.svm.train [-sp] group=name [subgroup=name] trainingmap=name signaturefile=name [type=name] [kernel=name] [cache=cache size] [degree=value] [gamma=value] [coef0=value] [eps=value] [cost=value] [nu=value] [p=value] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

### Flags:

-s
  Do not use the shrinking heuristics
  Defaults to use the shrinking heuristics
-p
  Train a SVC or SVR model for probability estimates
  Defaults to no probabilities in model
--overwrite
  Allow output files to overwrite existing files
--help
  Print usage summary
--verbose
  Verbose module output
--quiet
  Quiet module output
--ui
  Force launching GUI dialog

### Parameters:

group=name [required]
  Maps with feature values (attributes)
subgroup=name
  Name of input imagery subgroup
trainingmap=name [required]
  Map with training labels or target values
signaturefile=name [required]
  Name for output file containing result signatures
type=name
  Type of SVM
  Options: c_svc, nu_svc, one_class, epsilon_svr, nu_svr
  Default: c_svc
  c_svc: C-SVM classification
  nu_svc: nu-SVM classification
  one_class: one-class SVM
  epsilon_svr: epsilon-SVM regression
  nu_svr: nu-SVM regression
kernel=name
  SVM kernel type
  Options: linear, poly, rbf, sigmoid
  Default: rbf
  linear: u'*v
  poly: (gamma*u'*v + coef0)^degree
  rbf: exp(-gamma*|u-v|^2)
  sigmoid: tanh(gamma*u'*v + coef0)
cache=cache size
  LIBSVM kernel cache size in MB
  Options: 1-
  Default: 512
degree=value
  Degree in kernel function
  Options: 0-
  Default: 3
gamma=value
  Gamma in kernel function
  Default: 1
coef0=value
  coef0 in kernel function
  Default: 0
eps=value
  Tolerance of termination criterion
  Defaults to 0.00001 for nu-SVC and 0.001 for others
cost=value
  Cost of constraints violation
  The parameter C of C-SVC, epsilon-SVR, and nu-SVR
  Default: 1
nu=value
  The parameter nu of nu-SVC, one-class SVM, and nu-SVR
  Default: 0.5
p=value
  The epsilon in epsilon-insensitive loss function of epsilon-SVM regression
  Default: 0.1

## DESCRIPTION

i.svm.train finds parameters for a Support Vector Machine and stores them in a signature file for later usage by i.svm.predict.

Internally the module performs input value rescaling of each of imagery group rasters by mean normalisation based on minimum and maximum value present in the raster metadata. Rescaling parameters are written into the signature file for use during prediction.

## NOTES

i.svm.train internally is using the LIBSVM. For introduction into value prediction or estimation with LIBSVM, see a Practical Guide to Support Vector Classification by Chih-Wei Hsu, Chih-Chung Chang, and Chih-Jen Lin.

It is strongly suggested to have semantic labels set for each raster map in the training data (feature value) imagery group. Use r.support to set semantic labels.

## PERFORMANCE

SVM training is done by loading all training data into memory. In a case of large input raster files, use sparse label rasters (e.g. raster points or small patches instead of uninterrupted cover).

During the training process there is no progress output printed. Training with large number of data points can take significant time - just be patient.

By default the shrinking heuristics option of LIBSVM is enabled. It should not impact the outcome, just the training time. On some input parameter and data combinations training with the shrinking heuristics disabled might be faster.

The cache parameter determines the maximum memory allocated for kernel caching to enhance computational speed. It's important to note that the actual module's memory consumption may vary from this setting, as it solely impacts LIBSVM's internal caching. The cache is utilized on an as-needed basis, so it's unlikely to reach the specified value.

## EXAMPLE

This is the first part of classification process. See i.svm.predict for the second part.

Train a SVM to identify land use classes according to the 1996 land use map landuse96_28m and then classify a LANDSAT scene from October of 2002. Example requires the nc_spm_08 dataset.

    # Align computation region to the scene
    g.region raster=lsat7_2002_10 -p

    # store VIZ, NIR, MIR into group/subgroup
    i.group group=lsat7_2002 subgroup=res_30m \
        input=lsat7_2002_10,lsat7_2002_20,lsat7_2002_30,lsat7_2002_40,lsat7_2002_50,lsat7_2002_70

    # Now digitize training areas "training" with the digitizer
    # and convert to raster model with v.to.rast
    v.to.rast input=training output=training use=cat label_column=label
    # If you are just playing around and do not care about the accuracy of outcome,
    # just use one of existing maps instead e.g.
    # r.random input=landuse96_28m npoints=10000 raster=training -s

    # Train the SVM
    i.svm.train group=lsat7_2002 subgroup=res_30m \
        trainingmap=training signaturefile=landuse96_rnd_points

    # Go to i.svm.predict for the next step.

## SEE ALSO

Predict values: i.svm.predict
Set semantic labels: r.support
Other classification modules: i.maxlik, i.smap
LIBSVM home page: LIBSVM - A Library for Support Vector Machines

## REFERENCES

Please cite both - LIBSVM and i.svm.

- For i.svm.* modules:
  Nartiss, M., & Melniks, R. (2023). Improving pixel-based classification of GRASS GIS with support vector machine. Transactions in GIS, 00, 1–16. https://doi.org/10.1111/tgis.13102
- For LIBSVM:
  Chang, C.-C., & Lin, C.-J. (2011). LIBSVM : a library for support vector machines. ACM Transactions on Intelligent Systems and Technology, 2:27:1--27:27.

## AUTHOR

Maris Nartiss, University of Latvia.

## SOURCE CODE

Available at: i.svm.train source code (history)

Latest change: Thursday Nov 06 22:27:54 2025 in commit: 298b38614712934179355ea767403d6bfea8f5f9

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