pbclassif.rst

Classification
==============

Pixel based classification
--------------------------

Orfeo ToolBox ships with a set of application to perform supervised or
unsupervised pixel-based image classification. This framework allows
to learn from multiple images, and using several machine learning method
such as SVM, Bayes, KNN, Random Forests, Artificial Neural Network, and
others...(see application help of ``TrainImagesClassifier`` and
``TrainVectorClassifier`` for further details about all the available
classifiers). Here is an overview of the complete workflow:

1. Compute samples statistics for each image
2. Compute sampling rates for each image (only if more than one input image)
3. Select samples positions for each image
4. Extract samples measurements for each image
5. Compute images statistics
6. Train machine learning model from samples

Samples statistics estimation
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The first step of the framework is to know how many samples are
available for each class in your image. The ``PolygonClassStatistics``
will do this job for you. This application processes a set of training
geometries and an image and outputs statistics about available samples
(i.e. pixel covered by the image and out of a no-data mask if
provided), in the form of a XML file:

-  number of samples per class

-  number of samples per geometry

Supported geometries are polygons, lines and points. Depending on the
geometry type, this application behaves differently:

-  polygon: select pixels whose center falls inside the polygon

-  lines: select pixels intersecting the line

-  points: select closest pixel to the provided point

The application will require the input image, but it is only used to
define the footprint in which samples will be selected. The user can
also provide a raster mask, that will be used to discard pixel
positions, using parameter ``-mask``.

A simple use of the application ``PolygonClassStatistics`` could be as
follows :

::

    otbcli_PolygonClassStatistics  -in     LANDSAT_MultiTempIm_clip_GapF_20140309.tif
                                   -vec    training.shp 
                                   -field  CODE 
                                   -out    classes.xml

The ``-field`` parameter is the name of the field that corresponds to class
labels in the input geometries.

The output XML file will look like this::
   
   <?xml version="1.0" ?>
   <GeneralStatistics>
    <Statistic name="samplesPerClass">
        <StatisticMap key="11" value="56774" />
        <StatisticMap key="12" value="59347" />
        <StatisticMap key="211" value="25317" />
        <StatisticMap key="221" value="2087" />
        <StatisticMap key="222" value="2080" />
        <StatisticMap key="31" value="8149" />
        <StatisticMap key="32" value="1029" />
        <StatisticMap key="34" value="3770" />
        <StatisticMap key="36" value="941" />
        <StatisticMap key="41" value="2630" />
        <StatisticMap key="51" value="11221" />
    </Statistic>
    <Statistic name="samplesPerVector">
        <StatisticMap key="0" value="3" />
        <StatisticMap key="1" value="2" />
        <StatisticMap key="10" value="86" />
        <StatisticMap key="100" value="21" />
        <StatisticMap key="1000" value="3" />
        <StatisticMap key="1001" value="27" />
        <StatisticMap key="1002" value="7" />
        ...



Samples selection
~~~~~~~~~~~~~~~~~

Now, we know exactly how many samples are available in the image for
each class and each geometry in the training set. From this
statistics, we can now compute the sampling rates to apply for each
classes, and perform the sample selection. This will be done by the
``SampleSelection`` application.

There are several strategies to compute those sampling rates:

* **Constant strategy:** All classes will be sampled with the same number
  of samples, which is user-defined.
* **Smallest class strategy:** The class with the least number of samples
  will be fully sampled. All other classes will be sampled with the
  same number of samples.
* **Percent strategy:** Each class will be sampled with a user-defined
  percentage (same value for all classes) of samples available in this
  class.
* **Total strategy:** A global number of samples to generate is
  divided proportionally among each class (classes proportions are
  enforced).
* **Take all strategy:** Take all the available samples
* **By class strategy:** Set a target number of samples for each
  class. The number of samples for each class is read from a CSV file.

To actually select the sample positions, there are two available
sampler:

* **Random:** Randomly select samples while respecting the sampling
  rate
* **Periodic:** Sample periodically using the sampling rate

The application will make sure that samples spans the whole training
set extent by adjusting the sampling rate. Depending on the strategy
to determine the sampling rate, some geometries of the training set
might not be sampled.

The application will accept as input the input image and training
geometries, as well class statistics XML file computed during previous
step. It will output a vector file containing point geometries which
indicate the location of the samples.

::

   otbcli_SampleSelection -in LANDSAT_MultiTempIm_clip_GapF_20140309.tif
                          -vec training.shp
                          -instats classes.xml
                          -field CODE
                          -strategy smallest
                          -outrates rates.csv
                          -out samples.sqlite
    
The csv file written by the optional ``-outrates`` parameter sums-up what
has been done during samples selection::
     
     #className requiredSamples totalSamples rate
     11	 941	56774	0.0165745
     12	 941	59347	0.0158559
     211 941  25317	0.0371687
     221 941  2087	0.450886
     222 941  2080	0.452404
     31	 941	8149	0.115474
     32	 941	1029	0.91448
     34	 941	3770	0.249602
     36	 941	941 	1
     41	 941	2630	0.357795
     51	 941	11221	0.0838606


.. figure:: ../Art/ClassifImages/sample-selection.png

   This image shows the polygons of the training with a color
   corresponding to their class. The red dot shows the samples that
   have been selected.


Samples extraction
~~~~~~~~~~~~~~~~~~

Now that we selected the location of the samples, we will attach
measurement to them. This is the purpose of the ``SampleExtraction``
application. It will walk through the list of samples and extract the
underlying pixel values. If no ``-out`` parameter is given, the
``SampleExtraction`` application can work in update mode, thus allowing
to extract features from multiple images of the same location.

Features will be stored in fields attached to each sample. Field name
can be generated from a prefix a sequence of numbers (i.e. if
prefix is ``feature_`` then features will be named ``feature_0``,
``feature_1``, ...). This can be achieved with the ``-outfield prefix``
option. Alternatively, one can set explicit names for all features
using the ``-outfield list`` option.

::

   otbcli_SampleExtraction -in LANDSAT_MultiTempIm_clip_GapF_20140309.tif
                           -vec samples.sqlite
                           -outfield prefix
                           -outfield.prefix.name band_
                           -field CODE


.. figure:: ../Art/ClassifImages/samples-extraction.png

   Attributes table of the updated samples file. 
            

Working with several images
~~~~~~~~~~~~~~~~~~~~~~~~~~~

If the training set spans several images, the ``MultiImageSamplingRate``
application allows to compute the appropriate sampling rates per image
and per class, in order to get samples that spans the whole images
coverage.

It is first required to run the ``PolygonClassStatistics`` application
on each image of the set separately. The ``MultiImageSamplingRate``
application will then read all the produced statistics XML files and
derive the sampling rates according the sampling strategy. For more
information, please refer to the `Samples statistics estimation`_ section.

There are 3 modes for the sampling rates estimation from multiple
images:

* **Proportional mode:** For each class, the requested number of
  samples is divided proportionally among the images.
* **Equal mode:** For each class, the requested number of samples is
  divided equally among the images.
* **Custom mode:** The user indicates the target number of samples for
  each image.

The different behaviors for each mode and strategy are described as follows.

:math:`T_i( c )` and :math:`N_i( c )` refers resp. to the total number and needed number
of samples in image :math:`i` for class :math:`c`. Let's call :math:`L` the total number of
image.

* **Strategy = all**
  
  - Same behavior for all modes proportional, equal, custom : take all samples
  
* **Strategy = constant** (let's call :math:`M` the global number of samples per
  class required)

  - *Mode = proportional:* For each image :math:`i` and each class :math:`c`,
    :math:`N_i( c ) = \frac{M * T_i(c)}{sum_k(T_k(c))}`
  - *Mode = equal:* For each image :math:`i` and each class :math:`c`,
    :math:`N_i( c ) = \frac{M}{L}`
  - *Mode = custom:* For each image :math:`i` and each class :math:`c`,
    :math:`N_i( c ) = M_i` where :math:`M_i` is the custom requested number of samples
    for image i

* **Strategy = byClass** (let's call :math:`M(c)` the global number of samples for
  class c)

  - *Mode = proportional:* For each image :math:`i` and each class :math:`c`,
    :math:`N_i( c ) = M(c) * \frac{T_i( c )}{sum_k( T_k(c))}`
  - *Mode = equal:* For each image :math:`i` and each class :math:`c`,
    :math:`N_i( c ) = \frac{M(c)}{L}`
  - *Mode = custom:* For each image :math:`i` and each class :math:`c`,
    :math:`Ni( c ) = M_i(c)` where :math:`M_i(c)` is the custom requested number of
    samples for each image :math:`i` and each class :math:`c`

* **Strategy = percent**

  - *Mode = proportional:* For each image :math:`i` and each class :math:`c`,
    :math:`N_i( c ) = p * T_i(c)` where :math:`p` is the user-defined percentage
  - *Mode = equal:* For each image :math:`i` and each class :math:`c`,
    :math:`N_i( c ) = p * \frac{sum_k(Tk(c))}{L}` where :math:`p` is the user-defined percentage
  - *Mode = custom:* For each image :math:`i` and each class :math:`c`,
    :math:`Ni( c ) = p(i) * T_i(c)` where :math:`p(i)` is the user-defined percentage for image :math:`i`

* **Strategy = total**

  - *Mode = proportional:* For each image :math:`i` and each class :math:`c`,
    :math:`N_i( c ) = total * (\frac{sum_k(Ti(k))}{sum_kl(Tl(k))}) * (\frac{Ti(c)}{sum_k(Ti(k))})` where :math:`total` is the total number of samples specified
  - *Mode = equal:* For each image :math:`i` and each class :math:`c`,
    :math:`N_i( c ) = (total / L) * (\frac{Ti(c)}{sum_k(Ti(k))})` where :math:`total` is the total number of samples specified
  - *Mode = custom:* For each image :math:`i` and each class :math:`c`,
    :math:`Ni( c ) = total(i) * (\frac{Ti(c)}{sum_k(Ti(k))})` where :math:`total(i)` is the total number of samples specified for image :math:`i`
    
* **Strategy = smallest class**
      
  - *Mode = proportional:* the smallest class is computed globally, then this smallest size is used for the strategy constant+proportional
  - *Mode = equal:* the smallest class is computed globally, then this smallest size is used for the strategy constant+equal
  - *Mode = custom:* the smallest class is computed and used for each image separately

The ``MultiImageSamplingRate`` application can be used as follows:

::

   otbcli_MultiImageSamplingRate -il stats1.xml stats2.xml stats3.xml
                                 -out rates.csv
                                 -strategy smallest
                                 -mim proportional
    
          
The output filename from ``-out`` parameter will be used to generate as
many filenames as necessary (e.g. one per input filename), called
``rates_1.csv``, ``rates_2.csv`` ... 

Once rates are computed for each image, sample selection can be
performed on each corresponding image using the by class strategy:

::
   
   otbcli_SampleSelection -in img1.tif
                          -vec training.shp
                          -instats stats1.xml
                          -field CODE
                          -strategy byclass
                          -strategy.byclass.in rates_1.csv
                          -out samples1.sqlite

Samples extraction can then be performed on each image b y following
the `Samples extraction`_ step. The learning application can process
several samples files.
    
Images statistics estimation
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Some machine learning algorithms converge faster if the range of
features is :math:`[-1,1]` or :math:`[0,1]`. Other will be sensitive
to relative ranges between feature, e.g. a feature with a larger range
might have more weight in the final decision. This is for instance the
case for machine learning algorithm using euclidean distance at some
point to compare features. In those cases, it is advised to normalize
all features to the range :math:`[-1,1]` before performing the
learning. For this purpose, the ``ComputeImageStatistics`` application
allows to compute and output to an XML file the mean and standard
deviation based on pooled variance of each band for one or several
images.

::

    otbcli_ComputeImagesStatistics -il  im1.tif im2.tif im3.tif
                                   -out images_statistics.xml

The output statistics file can then be fed to the training and
classification applications.


Training the model
~~~~~~~~~~~~~~~~~~

Now that the training samples are ready, we can perform the learning
using the ``TrainVectorClassifier`` application.

::

   otbcli_TrainVectorClassifier -io.vd samples.sqlite
                                -cfield CODE
                                -io.out model.rf
                                -classifier rf
                                -feat band_0 band_1 band_2 band_3 band_4 band_5 band_6

The ``-classifier`` parameter allows to choose which machine learning
model algorithm to train. You have the possibility to do the unsupervised
classification,for it, you must to choose the Shark kmeans classifier.
Please refer to the ``TrainVectorClassifier`` application reference documentation.

In case of multiple samples files, you can add them to the ``-io.vd``
parameter (see  `Working with several images`_ section).

The feature to be used for training must be explicitly listed using
the ``-feat`` parameter. Order of the list matters.

If you want to use a statistic file for features normalization, you
can pass it using the ``-io.stats`` parameter. Make sure that the
order of feature statistics in the statistics file matches the order
of feature passed to the ``-feat`` option.

The field in vector data allowing to specify the label of each sample
can be set using the ``-cfield`` option.

By default, the application will estimate the trained classifier
performances on the same set of samples that has been used for
training. The ``-io.vd`` parameter allows to specify a different
samples file for this purpose, for a more fair estimation of the
performances. Note that this performances estimation scheme can also
be estimated afterward (see `Validating the classification model`_
section).
                     

Using the classification model
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Once the classifier has been trained, one can apply the model to
classify pixel inside defined classes on a new image using the
*ImageClassifier* application:

::

    otbcli_ImageClassifier -in     image.tif
                           -model  model.rf
                           -out    labeled_image.tif

You can set an input mask to limit the classification to the mask area
with value >0.

-imstat images_statistics.xml

Validating the classification model
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The performance of the model generated by the *TrainImagesClassifier*
application is directly estimated by the application itself, which
displays the precision, recall and F-score of each class, and can
generate the global confusion matrix as an output \*.CSV file.

With the *ConputeConfusionMatrix* application, it is also possible to
estimate the performance of a model from a classification map generated
with the *ImageClassifier* application. This labeled image is compared
to positive reference samples (either represented as a raster labeled
image or as a vector data containing the reference classes). It will
compute the confusion matrix and precision, recall and F-score of each
class too, based on the
`ConfusionMatrixCalculator <http://www.orfeo-toolbox.org/doxygen-current/classotb_1_1ConfusionMatrixCalculator.html>`_ 
class.

If you have made an unsupervised classification, it must be specified
to the ``ConputeConfusionMatrix`` application. In this case, a contingency table
have to be create rather than a confusion matrix. For further details,
see ``format`` parameter in the application help of *ConputeConfusionMatrix*.

::

    otbcli_ComputeConfusionMatrix -in                labeled_image.tif
                                  -ref               vector
                                  -ref.vector.in     vectordata.shp
                                  -ref.vector.field  Class (name_of_label_field)
                                  -out               confusion_matrix.csv

.. _fancy_classification_results:

Fancy classification results
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Color mapping can be used to apply color transformations on the final
gray level label image. It allows to get an RGB classification map by
re-mapping the image values to be suitable for display purposes. One can
use the *ColorMapping* application. This tool will replace each label
with an 8-bits RGB color specified in a mapping file. The mapping file
should look like this :

::

    # Lines beginning with a # are ignored
    1 255 0 0

In the previous example, 1 is the label and 255 0 0 is a RGB color (this
one will be rendered as red). To use the mapping tool, enter the
following :

::

    otbcli_ColorMapping -in                labeled_image.tif
                        -method            custom
                        -method.custom.lut lut_mapping_file.txt
                        -out               RGB_color_image.tif

Other look-up tables (LUT) are available : standard continuous LUT,
optimal LUT, and LUT computed over a support image.

Example
~~~~~~~

We consider 4 classes: water, roads, vegetation and buildings with red
roofs. Data is available in the OTB-Data
`repository <http://hg.orfeo-toolbox.org/OTB-Data/file/0fed8f4f035c/Input/Classification>`_ 
and this image is produced with the commands inside this
`file <http://hg.orfeo-toolbox.org/OTB-Applications/file/3ce975605013/Testing/Classification/CMakeLists.txt>`_ .

.. |image_21| image:: ../Art/MonteverdiImages/classification_chain_inputimage.jpg
.. |image_22| image:: ../Art/MonteverdiImages/classification_chain_fancyclassif_fusion.jpg
.. |image_23| image:: ../Art/MonteverdiImages/classification_chain_fancyclassif.jpg

.. _Figure2:


+---------------------------+---------------------------+---------------------------+
|        |image_21|         |         |image_22|        |          |image_23|       |
+---------------------------+---------------------------+---------------------------+

Figure 2: From left to right: Original image, result image with fusion (with monteverdi viewer) of original image and fancy classification and input image with fancy color classification from labeled image.


Fusion of classification maps
-----------------------------

After having processed several classifications of the same input image
but from different models or methods (SVM, KNN, Random Forest,...), it
is possible to make a fusion of these classification maps with the
*FusionOfClassifications* application which uses either majority voting
or the Dempster-Shafer framework to handle this fusion. The Fusion of
Classifications generates a single more robust and precise
classification map which combines the information extracted from the
input list of labeled images.

The *FusionOfClassifications* application has the following input parameters:

-  ``-il`` list of input labeled classification images to fuse

-  ``-out`` the output labeled image resulting from the fusion of the
   input classification images

-  ``-method`` the fusion method (either by majority voting or by
   Dempster Shafer)

-  ``-nodatalabel`` label for the no data class (default value = 0)

-  ``-undecidedlabel`` label for the undecided class (default value = 0)

The input pixels with the no-data class label are simply ignored by the
fusion process. Moreover, the output pixels for which the fusion process
does not result in a unique class label, are set to the undecided value.

Majority voting for the fusion of classifications
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In the Majority Voting method implemented in the
*FusionOfClassifications* application, the value of each output pixel is
equal to the more frequent class label of the same pixel in the input
classification maps. However, it may happen that the more frequent class
labels are not unique in individual pixels. In that case, the undecided
label is attributed to the output pixels.

The application can be used like this:

::

    otbcli_FusionOfClassifications  -il             cmap1.tif cmap2.tif cmap3.tif
                                    -method         majorityvoting
                                    -nodatalabel    0
                                    -undecidedlabel 10
                                    -out            MVFusedClassificationMap.tif

Let us consider 6 independent classification maps of the same input
image (Cf. left image in Figure2_) generated from 6 different SVM models. 
The Figure3_ represents them after a color mapping by the same LUT. 
Thus, 4 classes (water: blue, roads: gray,vegetation: green, 
buildings with red roofs: red) are observable on each of them.

.. |image_31| image:: ../Art/MonteverdiImages/QB_1_ortho_C1_CM.png
.. |image_32| image:: ../Art/MonteverdiImages/QB_1_ortho_C2_CM.png
.. |image_33| image:: ../Art/MonteverdiImages/QB_1_ortho_C3_CM.png
.. |image_34| image:: ../Art/MonteverdiImages/QB_1_ortho_C4_CM.png
.. |image_35| image:: ../Art/MonteverdiImages/QB_1_ortho_C5_CM.png
.. |image_36| image:: ../Art/MonteverdiImages/QB_1_ortho_C6_CM.png

.. _Figure3:

+---------------------------+---------------------------+---------------------------+
|        |image_31|         |         |image_32|        |          |image_33|       |
+---------------------------+---------------------------+---------------------------+
|        |image_34|         |         |image_35|        |          |image_36|       |
+---------------------------+---------------------------+---------------------------+

Figure 3: Six fancy colored classified images to be fused, generated from 6 different SVM models. 


As an example of the *FusionOfClassifications* application by *majority
voting*, the fusion of the six input classification maps represented in
Figure3_ leads to the classification map illustrated on the right in Figure4_.
Thus, it appears that this fusion highlights the more relevant classes among the six different
input classifications. The white parts of the fused image correspond to
the undecided class labels, i.e. to pixels for which there is not a
unique majority voting.

.. |image_41| image:: ../Art/MonteverdiImages/classification_chain_inputimage.jpg
.. |image_42| image:: ../Art/MonteverdiImages/QB_1_ortho_MV_C123456_CM.png

.. _Figure4:

+------------------------------------------------+------------------------------------------------+
|                   |image_41|                   |                   |image_42|                   |
+------------------------------------------------+------------------------------------------------+

Figure 4: From left to right: Original image, and fancy colored classified image obtained by a majority voting fusion of the 6 classification maps represented in Fig. 4.13 (water: blue, roads: gray, vegetation: green, buildings with red roofs: red, undecided: white)

Dempster Shafer framework for the fusion of classifications
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The *FusionOfClassifications* application, handles another method to
compute the fusion: the Dempster Shafer framework. In the
`Dempster-Shafer
theory <http://en.wikipedia.org/wiki/Dempster-Shafer_theory>`_ , the
performance of each classifier resulting in the classification maps to
fuse are evaluated with the help of the so-called *belief function* of
each class label, which measures the degree of belief that the
corresponding label is correctly assigned to a pixel. For each
classifier, and for each class label, these belief functions are
estimated from another parameter called the *mass of belief* of each
class label, which measures the confidence that the user can have in
each classifier according to the resulting labels.

In the Dempster Shafer framework for the fusion of classification maps,
the fused class label for each pixel is the one with the maximal belief
function. In case of multiple class labels maximizing the belief
functions, the output fused pixels are set to the undecided value.

In order to estimate the confidence level in each classification map,
each of them should be confronted with a ground truth. For this purpose,
the masses of belief of the class labels resulting from a classifier are
estimated from its confusion matrix, which is itself exported as a
\*.CSV file with the help of the *ComputeConfusionMatrix* application.
Thus, using the Dempster-Shafer method to fuse classification maps needs
an additional input list of such \*.CSV files corresponding to their
respective confusion matrices.

The application can be used like this:

::

    otbcli_FusionOfClassifications  -il             cmap1.tif cmap2.tif cmap3.tif
                                    -method         dempstershafer
                                    -method.dempstershafer.cmfl
                                                    cmat1.csv cmat2.csv cmat3.csv
                                    -nodatalabel    0
                                    -undecidedlabel 10
                                    -out            DSFusedClassificationMap.tif

As an example of the *FusionOfClassifications* application by *Dempster
Shafer*, the fusion of the six input classification maps represented in Figure3_
leads to the classification map illustrated on the right in Figure5_.
Thus, it appears that this fusion gives access to a more precise and robust classification map
based on the confidence level in each classifier.


.. |image_51| image:: ../Art/MonteverdiImages/classification_chain_inputimage.jpg
.. |image_52| image:: ../Art/MonteverdiImages/QB_1_ortho_DS_V_P_C123456_CM.png

.. _Figure5:

+------------------------------------------------+------------------------------------------------+
|                   |image_51|                   |                   |image_52|                   |
+------------------------------------------------+------------------------------------------------+

Figure 5: From left to right: Original image, and fancy colored classified image obtained by a Dempster-Shafer fusion of the 6 classification maps represented in Figure3_ (water: blue, roads: gray, vegetation: green, buildings with red roofs: red, undecided: white).


Recommendations to properly use the fusion of classification maps
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In order to properly use the *FusionOfClassifications* application, some
points should be considered. First, the ``list_of_input_images`` and
``OutputFusedClassificationImage`` are single band labeled images, which
means that the value of each pixel corresponds to the class label it
belongs to, and labels in each classification map must represent the
same class. Secondly, the undecided label value must be different from
existing labels in the input images in order to avoid any ambiguity in
the interpretation of the ``OutputFusedClassificationImage``.

Majority voting based classification map regularization
-------------------------------------------------------

Resulting classification maps can be regularized in order to smooth
irregular classes. Such a regularization process improves classification
results by making more homogeneous areas which are easier to handle.

Majority voting for the classification map regularization
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The *ClassificationMapRegularization* application performs a
regularization of a labeled input image based on the Majority Voting
method in a specified ball shaped neighborhood. For each center pixel,
Majority Voting takes the more representative value of all the pixels
identified by the structuring element and then sets the output center
pixel to this majority label value. The ball shaped neighborhood is
identified by its radius expressed in pixels.

Handling ambiguity and not classified pixels in the majority voting based regularization
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Since, the Majority Voting regularization may lead to not unique
majority labels in the neighborhood, it is important to define which
behaviour the filter must have in this case. For this purpose, a Boolean
parameter (called ip.suvbool) is used in the
*ClassificationMapRegularization* application to choose whether pixels
with more than one majority class are set to Undecided (true), or to
their Original labels (false = default value).

Moreover, it may happen that pixels in the input image do not belong to
any of the considered class. Such pixels are assumed to belong to the
NoData class, the label of which is specified as an input parameter for
the regularization. Therefore, those NoData input pixels are invariant
and keep their NoData label in the output regularized image.

The *ClassificationMapRegularization* application has the following
input parameters :

-  ``-io.in`` labeled input image resulting from a previous
   classification process

-  ``-io.out`` output labeled image corresponding to the regularization
   of the input image

-  ``-ip.radius`` integer corresponding to the radius of the ball shaped
   structuring element (default value = 1 pixel)

-  ``-ip.suvbool`` boolean parameter used to choose whether pixels with
   more than one majority class are set to Undecided (true), or to their
   Original labels (false = default value). Please note that the
   Undecided value must be different from existing labels in the input
   image

-  ``-ip.nodatalabel`` label for the NoData class. Such input pixels
   keep their NoData label in the output image (default value = 0)

-  ``-ip.undecidedlabel`` label for the Undecided class (default value =
   0).

The application can be used like this:

::

    otbcli_ClassificationMapRegularization  -io.in              labeled_image.tif
                                            -ip.radius          3
                                            -ip.suvbool         true
                                            -ip.nodatalabel     10
                                            -ip.undecidedlabel  7
                                            -io.out             regularized.tif

Recommendations to properly use the majority voting based regularization
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In order to properly use the *ClassificationMapRegularization*
application, some points should be considered. First, both
``InputLabeledImage`` and ``OutputLabeledImage`` are single band labeled
images, which means that the value of each pixel corresponds to the
class label it belongs to. The ``InputLabeledImage`` is commonly an
image generated with a classification algorithm such as the SVM
classification. Remark: both ``InputLabeledImage`` and
``OutputLabeledImage`` are not necessarily of the same type.
Secondly, if ip.suvbool == true, the Undecided label value must be
different from existing labels in the input labeled image in order to
avoid any ambiguity in the interpretation of the regularized
``OutputLabeledImage``. Finally, the structuring element radius must
have a minimum value equal to 1 pixel, which is its default value. Both
NoData and Undecided labels have a default value equal to 0.

Example
~~~~~~~

Resulting from the application presented in section :ref:`fancy_classification_results`
and illustrated in Figure2_, the Figure6_ shows a regularization
of a classification map composed of 4 classes: water, roads, vegetation
and buildings with red roofs. The radius of the ball shaped structuring
element is equal to 3 pixels, which corresponds to a ball included in a
7 x 7 pixels square. Pixels with more than one majority class keep their
original labels.



Regression
----------

The machine learning models in OpenCV and LibSVM also support a
regression mode : they can be used to predict a numeric value (i.e. not
a class index) from an input predictor. The workflow is the same as
classification. First, the regression model is trained, then it can be
used to predict output values. The applications to do that are and .

.. |image_61| image:: ../Art/MonteverdiImages/classification_chain_inputimage.jpg
.. |image_62| image:: ../Art/MonteverdiImages/classification_chain_fancyclassif_CMR_input.png
.. |image_63| image:: ../Art/MonteverdiImages/classification_chain_fancyclassif_CMR_3.png


.. _Figure6:

+---------------------------+---------------------------+---------------------------+
|        |image_61|         |         |image_62|        |          |image_63|       |
+---------------------------+---------------------------+---------------------------+
	 
Figure 6: From left to right: Original image, fancy colored classified image and regularized classification map with radius equal to 3 pixels. 

The input data set for training must have the following structure :

-  *n* components for the input predictors

-  one component for the corresponding output value

The application supports 2 input formats :

-  An image list : each image should have components matching the
   structure detailed earlier (*n* feature components + 1 output value)

-  A CSV file : the first *n* columns are the feature components and the
   last one is the output value

If you have separate images for predictors and output values, you can
use the application.

::

    otbcli_ConcatenateImages  -il features.tif  output_value.tif
                              -out training_set.tif

Statistics estimation
~~~~~~~~~~~~~~~~~~~~~

As in classification, a statistics estimation step can be performed
before training. It allows to normalize the dynamic of the input
predictors to a standard one : zero mean, unit standard deviation. The
main difference with the classification case is that with regression,
the dynamic of output values can also be reduced.

The statistics file format is identical to the output file from
application, for instance :

::

    <?xml version="1.0" ?>
    <FeatureStatistics>
        <Statistic name="mean">
            <StatisticVector value="198.796" />
            <StatisticVector value="283.117" />
            <StatisticVector value="169.878" />
            <StatisticVector value="376.514" />
        </Statistic>
        <Statistic name="stddev">
            <StatisticVector value="22.6234" />
            <StatisticVector value="41.4086" />
            <StatisticVector value="40.6766" />
            <StatisticVector value="110.956" />
        </Statistic>
    </FeatureStatistics>

In the application, normalization of input predictors and output values
is optional. There are 3 options :

-  No statistic file : normalization disabled

-  Statistic file with *n* components : normalization enabled for input
   predictors only

-  Statistic file with *n+1* components : normalization enabled for
   input predictors and output values

If you use an image list as training set, you can run application. It
will produce a statistics file suitable for input and output
normalization (third option).

::

    otbcli_ComputeImagesStatistics  -il   training_set.tif
                                    -out  stats.xml

Training
~~~~~~~~

Initially, the machine learning models in OTB only used classification.
But since they come from external libraries (OpenCV and LibSVM), the
regression mode was already implemented in these external libraries. So
the integration of these models in OTB has been improved in order to
allow the usage of regression mode. As a consequence , the machine
learning models have nearly the same set of parameters for
classification and regression mode.

.. |image11| image:: ../Art/MonteverdiImages/classification_chain_inputimage.jpg
.. |image12| image:: ../Art/MonteverdiImages/QB_1_ortho_MV_C123456_CM.png
.. |image13| image:: ../Art/MonteverdiImages/classification_chain_inputimage.jpg
.. |image14| image:: ../Art/MonteverdiImages/QB_1_ortho_DS_V_P_C123456_CM.png

.. |image15| image:: ../Art/MonteverdiImages/classification_chain_inputimage.jpg
             :scale: 88%

-  Decision Trees

-  Gradient Boosted Trees

-  Neural Network

-  Random Forests

-  K-Nearest Neighbors

The behavior of application is very similar to . From the input data
set, a portion of the samples is used for training, whereas the other
part is used for validation. The user may also set the model to train
and its parameters. Once the training is done, the model is stored in an
output file.

::

    otbcli_TrainRegression  -io.il                training_set.tif
                            -io.imstat            stats.xml
                            -io.out               model.txt
                            -sample.vtr           0.5
                            -classifier           knn
                            -classifier.knn.k     5
                            -classifier.knn.rule  median

Prediction
~~~~~~~~~~

Once the model is trained, it can be used in application to perform the
prediction on an entire image containing input predictors (i.e. an image
with only *n* feature components). If the model was trained with
normalization, the same statistic file must be used for prediction. The
behavior of with respect to statistic file is identical to :

-  no statistic file : normalization off

-  *n* components : input only

-  *n+1* components : input and output

The model to use is read from file (the one produced during training).

::

    otbcli_PredictRegression  -in     features_bis.tif
                              -model  model.txt
                              -imstat stats.xml
                              -out    prediction.tif