CGAL 6.1 - Classification

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CGAL::Classification::Sum_of_weighted_features_classifier Class Reference
Reference Manual » Classifiers

`#include <CGAL/Classification/Sum_of_weighted_features_classifier.h>`

## Definition

Classifier based on the sum of weighted features with user-defined effects on labels.

Is model of
  `CGAL::Classification::Classifier`

## Public Types
enum | Effect { FAVORING = 0 , NEUTRAL = 1 , PENALIZING = 2 }
| Defines the effect of a feature on a type. More...

## Constructor
| Sum_of_weighted_features_classifier (const Label_set &labels, const Feature_set &features)
| instantiates the classifier using the sets of `labels` and `features`.

## Weights and Effects
void | set_weight (Feature_handle feature, float weight)
| sets the weight of `feature` (`weight` must be positive).
float | weight (Feature_handle feature) const
| returns the weight of `feature`.
void | set_effect (Label_handle label, Feature_handle feature, Effect effect)
| sets the `effect` of `feature` on `label`.
Effect | effect (Label_handle label, Feature_handle feature) const
| returns the `effect` of `feature` on `label`.

## Training
template<typename ConcurrencyTag , typename LabelIndexRange >
float | train (const LabelIndexRange &ground_truth, unsigned int nb_tests=300)
| runs the training algorithm.

## Input/Output
void | save_configuration (std::ostream &output)
| saves the current configuration in the stream `output`.
bool | load_configuration (std::istream &input, bool verbose=false)
| loads a configuration from the stream `input`.

## Member Enumeration Documentation

## ◆ Effect

enum CGAL::Classification::Sum_of_weighted_features_classifier::Effect

Defines the effect of a feature on a type.

Enumerator
FAVORING | High values of the feature favor this type.
NEUTRAL | The feature has no effect on this type.
PENALIZING | Low values of the feature favor this type.

## Constructor & Destructor Documentation

## ◆ Sum_of_weighted_features_classifier()

CGAL::Classification::Sum_of_weighted_features_classifier::Sum_of_weighted_features_classifier | ( | const Label_set & | labels,
|  | const Feature_set & | features
| ) |  |

instantiates the classifier using the sets of `labels` and `features`.

Note
  If the label set of the feature set are modified after instantiating this object (addition of removal of a label and/or of a feature), another classifier object should be instantiated as the internal data structures of this one are invalidated.

## Member Function Documentation

## ◆ load_configuration()

bool CGAL::Classification::Sum_of_weighted_features_classifier::load_configuration | ( | std::istream & | input,
|  | bool | verbose = `false`
| ) |  |

loads a configuration from the stream `input`.

A configuration is a set of weights and effects.

The input file should be in the XML format written by the `save_configuration()` method. Labels and features are described in the XML file by their name and the corresponding `Label` and `Feature_base` object should therefore be given the same names as the ones they had when saving the configuration.

Note
  If a feature (or label) found in the input file is not found in the `Feature_set` (`Label_set`) provided by the user in the constructor, and if `verbose` is set up to `true`, a warning is displayed.
  If a feature (or label) provided by the user in the constructor is not described in the input file, the corresponding weights and effects are kept to their default values (1 for the weight and `NEUTRAL` for the effect).

Parameters

  input | input stream.
  verbose | displays warning if set to `true`. The method is silent otherwise.

Returns
  `true` if all weights and effects found in the configuration file were applicable to the feature set and label set of this classifier, `false` otherwise.

## ◆ save_configuration()

void CGAL::Classification::Sum_of_weighted_features_classifier::save_configuration | ( | std::ostream & | output | ) |

saves the current configuration in the stream `output`.

This allows to easily save and recover a specific classification configuration, that is to say:

- The weight of each feature
- The effects of each feature on each label

The output file is written in an XML format that is readable by the `load_configuration()` method.

## ◆ train()

template<typename ConcurrencyTag , typename LabelIndexRange >

float CGAL::Classification::Sum_of_weighted_features_classifier::train | ( | const LabelIndexRange & | ground_truth,
|  | unsigned int | nb_tests = `300`
| ) |  |

runs the training algorithm.

From the set of provided ground truth, this algorithm estimates the sets of weights and effects that produce the most accurate result with respect to this ground truth. Old weights and effects are discarded.

Precondition
  At least one ground truth item should be assigned to each label.

Parameters

  ground_truth | vector of label indices. It should contain for each input item, in the same order as the input set, the index of the corresponding label in the `Label_set` provided in the constructor. Input items that do not have a ground truth information should be given the value `-1`.
  nb_tests | number of tests to perform. Higher values may provide the user with better results at the cost of a higher computation time. Using a value of at least 10 times the number of features is advised.

Returns
  mean intersection-over-union over each label between the provided ground truth and the best classification found by the training set.