/**
  \page tutorial-pf-curve-fitting Tutorial: Using Particle Filter to model a wire using polynomial interpolation
  \tableofcontents

\section tuto-pf-cf-intro Introduction

We suppose that you are already familiar with the \ref tutorial-pf.

The Particle Filters (PF) are a set of Monte Carlo algorithms that
permit to approximate solutions for filtering problems even when
the state-space and/or measurement space are non-linear.

In this tutorial, we will use a PF to model a wire using polynomial interpolation . The PF is used to
filter the noisy pixels in a segmented image in order to compute a model of the wire using polynomial interpolation.
The color wire is observed by a static camera, in the following configuration:

\htmlonly <style>div.image img[src="img-tutorial-pf-cf-illustration.jpg"]{width:50%;}</style>
\endhtmlonly
\image html img-tutorial-pf-cf-illustration.jpg

\subsection tuto-pf-cf-intro-methods The maths beyond the Particle Filter

The maths beyond the Particle Filter are explained in the documentation of the vpParticleFilter class.
They are also explained in the \ref tuto-pf-cf-intro-methods .

\section tuto-pf-cf-tutorial Explanations about the tutorial

The tutorial is split in three different programs:
- \ref tutorial-pf-curve-fitting-lms.cpp : this program illustrates how to perform a polynomial interpolation using the
Least-Mean Square method, and the impact of noise on the resulting interpolated model.
- \ref tutorial-pf-curve-fitting-pf.cpp : this program illustrates how to perform a polynomial interpolation using a
Particle Filter.
- \ref tutorial-pf-curve-fitting-all.cpp : this program uses the methods mentionned above to compare their performances.

\subsection tuto-pf-cf-tutorial-howtorun How to run the tutorial

To run one of the tutorials with the default dataset, please run the following commands:

```
$ cd $VISP_WS/visp-build/tutorial/particle-filter-curve-fitting
$ ./tutorial-pf-curve-fitting-{lms, pf, all} --video data/color_image_0%03d.png
```

To see the arguments the program can take, please run:

```
$ cd $VISP_WS/visp-build/tutorial/particle-filter-curve-fitting
$ ./tutorial-pf-curve-fitting-{lms, pf, all} -h
```

You should see something similar to the following image:

\htmlonly <style>div.image img[src="img-tutorial-pf-cf-helper"]{width:50%;}</style>
\endhtmlonly
\image html img-tutorial-pf-cf-helper.jpg "Screenshot of the tutorial Graphical User Interface"

For the tutorial-pf-curve-fitting-pf.cpp and tutorial-pf-curve-fitting-all.cpp tutorials, the PF must
be initialized. You are asked if you would rather use a manual initialization (left click) or an automatic one (right click).

\htmlonly <style>div.image img[src="img-tutorial-pf-cf-init"]{width:50%;}</style>
\endhtmlonly
\image html img-tutorial-pf-cf-init.jpg "Screenshot of the tutorial initialization step"

Then, for all the tutorials, you can either display the images one-by-one (left click) or automatically switch from an
image to the next one (middle click). You can leave the program whenever you want using a right click.

\htmlonly <style>div.image img[src="img-tutorial-pf-cf-run"]{width:50%;}</style>
\endhtmlonly
\image html img-tutorial-pf-cf-run.jpg "Screenshot of the tutorial during its run step"

\subsection tuto-pf-cf-tutorial-general General explanations about the tutorials

\subsubsection tuto-pf-cf-tutorial-general-segmentation Notes about the segmentation and skeletonization of the image

The segmentation of the image using HSV encoding has been presented in the \ref tutorial-hsv-range-tuner .

A calibration file containing the segmentation parameters for the default sequence can be found in the calib folder.
If you want to use your own sequence, please run the \ref tutorial-hsv-range-tuner.cpp tutorial to extract the
parameters that correspond to your own sequence and edit the file calib/hsv-thresholds.yml .

The skeletonization of the segmented image is not the topic of this tutorial. Thus, we invite the interested readers
to read by themselves the corresponding method in the \ref vpTutoSegmentation.cpp file.

\subsubsection tuto-pf-cf-tutorial-general-PF Explanations about the Particle Filter

The internal state of the PF contains the coefficients of the interpolation polynomial. Be
\f$ v(u) = \sum_{i=0}^N a_i u^i \f$ the interpolation polynomial whose highest degree is N.
The internal state of the PF is of size N + 1 such as:

\f[
  \begin{array}{lcl}
  \textbf{x}[i] &=& a_i
  \end{array}
\f]

The measurement \f$ \textbf{z} \f$ corresponds to the vector of vpImagePoint that forms the skeletonized version of the
segmented image.
Be \f$ u_i \f$ and \f$ v_i \f$ the horizontal and vertical pixel coordinates of the \f$ i^{th} \f$ marker.
The measurement vector can be written as:

\f[
  \begin{array}{lcl}
  \textbf{z}[i] &=& vpImagePoint(v_i , u_i)
  \end{array}
\f]


\subsubsection tuto-pf-cf-tutorial-general-LMS Explanations about the Least-Mean Square method

The Least-Mean Square method is a standard method to solve a polynomial interpolation problem.
The polynomial interpolation problem can be written in matrices form as follow:

\f[
\begin{array}{llcl}
  & \textbf{A}\textbf{x} &=& \textbf{b} \\
  \iff & \textbf{X} &=& \textbf{A}^+\textbf{b} \\
\end{array}
\f]

where \f$ \textbf{A}^+ \f$ denotes the Moore-Penrose pseudo-inverse of the matrix A, with:

\f[
\begin{array}{lcl}
  \textbf{A}[i][j] &=& u_i^j
\end{array}
\\
\begin{array}{lcl}
  \textbf{x}[i] &=& a_i
\end{array}
\\
\begin{array}{lcl}
  \textbf{b}[i] &=& v_i
\end{array}
\f]

<b>Important note:</b> due to numerical unstability, the pixel coordinates cannot be used directly
in the Least-Mean square method. Indeed, using pixel coordinates leads to having an ill-conditionned
\f$ \textbf{A} \f$ matrix. Consequently, in all the tutorials, the pixel coordinates are normalized
by dividing them by the height and width of the image before running any interpolation.

\subsection tuto-pf-cf-tutorial-explained Detailed explanations about the tutorials

We will now present the different tutorials and explained their important parts.

\subsubsection tuto-pf-cf-tutorial-explained-lms Details on the tutorial-pf-curve-fitting-lms.cpp

This tutorial goal is to show how a Least-Mean Square method can be used to perform polynomial interpolation
and the impact of noise on such technique.

To visualize the accuracy of the method, a vpPlot is instantiated in the following part of the code:

\snippet tutorial-pf-curve-fitting-lms.cpp Init_plot

At each iteration, the new frame is read, then segmented and skeletonized in the following section of code:

\snippet tutorial-pf-curve-fitting-lms.cpp Measurements_extraction

The method addSaltAndPepperNoise permits to add a user-defined percentage of salt-and-pepper noise, to evaluate the
robustness of the method against noise.

The polynomial interpolation is performed in the following section of the code:

\snippet tutorial-pf-curve-fitting-lms.cpp LMS_interpolation

It relies on the following method of the vpTutoMeanSquareFitting class:

\snippet vpTutoMeanSquareFitting.cpp Solve_LMS_system

The matrices that form the system that needs to be solved are filled in the vpTutoParabolaModel class (we remind the
reader that normalization of the pixel coordinates is performed to avoid numerical unstability):

\snippet vpTutoParabolaModel.h Fill_LMS_system

\subsubsection tuto-pf-cf-tutorial-explained-pf Details on the tutorial-pf-curve-fitting-pf.cpp

This tutorial is meant to show how a Particle Filter could be used to model a wire thanks to
polynomial interpolation.

To initialize a Particle Filter, a guess of the initial state must be given to it. The more accurate
is the initial guess, the quicker the PF will converge. The initialization can be done either manually or
automatically thanks to the following piece of code:

\snippet tutorial-pf-curve-fitting-pf.cpp Initialization_function

A Particle Filter needs a function to evaluate the likelihood of a particle. We decided to use a Gaussian-based function
that penalizes particles whose polynomial model has a Root Mean Square Error with regard to the measurement points greater than a given threshold.
To be robust against outliers, we use the Tukey M-estimator. The likelihood function is implemented in a functor
to be able to pass additional information such as the height and width of the input image:

\snippet tutorial-pf-curve-fitting-pf.cpp Likelihood_functor

This likelihood functor compute the residuals using the following evaluation functions:

\snippet tutorial-pf-curve-fitting-pf.cpp Evaluation_functions

A Particle Filter needs to perform a weighted average to compute the filtered state. Performing a weighted average of
the particles polynomial coefficients would not lead to satisfying results, as it is not mathematically correct.
Instead, we decided to generate a given number of "control points" by each particle. The number of control points generated
by a particle is dictated by its associated weight. Then, we compute the polynomial coefficients that best fit all these
control points using a Least-Square minimization technique. The weighted average is performed thanks to the following
functor:

\snippet tutorial-pf-curve-fitting-pf.cpp Average_functor

A Particle Filter needs a process function to project the particles forward in time. For this scenario,
we decided to use the identity, and let the randomness of the Particle Filter manage the potential motion
of the wire.

\snippet tutorial-pf-curve-fitting-pf.cpp Process_function

The initialization parameters of the Particle Filter are defined in the following section of code:

\snippet tutorial-pf-curve-fitting-pf.cpp Constants_for_the_PF

The initialization functions of the Particle Filter are defined in the following section of code:

\snippet tutorial-pf-curve-fitting-pf.cpp Init_functions

The Particle Filter is then constructed thanks to the following lines:

\snippet tutorial-pf-curve-fitting-pf.cpp Init_PF

Finally, the filtering is performed thanks to the following line:

\snippet tutorial-pf-curve-fitting-pf.cpp Perform_filtering

The filtered state is retrieve thanks to the following line:

\snippet tutorial-pf-curve-fitting-pf.cpp Get_filtered_state

\subsubsection tuto-pf-cf-tutorial-explained-all Details on the tutorial-pf-curve-fitting-all.cpp

The \ref tutorial-pf-curve-fitting-all.cpp reuse what has already been presented in the \ref tuto-pf-cf-tutorial-explained-lms
and \ref tuto-pf-cf-tutorial-explained-pf sections.

Its main objective is to compare the time performances and robustness against noise of the two methods.
The ratio of noise can be set using the Command Line Interface using the --noise option. For instance,

\code
$ ./tutorial-pf-curve-fitting-all --video data/color_image_0%03d.png --noise <ratio in the intervall [0.; 1.[>
\endcode

will add 50% of noisy pixels to the skeletonized image.

You can experiment by varying this parameter (and others as well) to see the impact on the different methods.
With 15% noisy pixels and more, the Particle Filter tends to have a greater accuracy than the LMS method, but
it takes more times to run.
*/
