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/**
\page tutorial-plotter Tutorial: Real-time curves plotter tool
\tableofcontents
This tutorial focuses on real-time curves drawing. It shows how to modify tutorial-ibvs-4pts.cpp introduced in
\ref tutorial-ibvs to draw the evolution of the visual features error and the camera velocity skew vector during an
image-based visual servoing.
Note that all the material (source code and images) described in this tutorial is part of ViSP source code
(in `tutorial/visual-servoing/ibvs` folder) and could be found in
https://github.com/lagadic/visp/tree/master/tutorial/visual-servoing/ibvs.
The modified code also available in tutorial-ibvs-4pts-plotter.cpp is the following.
\include tutorial-ibvs-4pts-plotter.cpp
The last image of the drawing is the following:
\image html img-ibvs-plotter.jpg Last image produced by the plotter.
Now we describe the new lines that were introduced:
\code
#include <visp3/core/vpPlot.h>
\endcode
Include the header of the vpPlot class that allows curves drawing.
\code
#ifdef VISP_HAVE_DISPLAY
vpPlot plotter(2, 250*2, 500, 100, 200, "Real time curves plotter");
\endcode
Since the plotter opens a windows to display the graphics, the usage of vpPlot class is only possible if ViSP is build
with a 3rd party that allows display capabilities; either libx11, GDI, OpenCV or GTK. If this is the case, we create an
instance of the vpPlot class. The window that is created will contain two graphics. The windows size will be 500 by 500
pixels. The window position will be (100, 200), and the title "Real time curves plotter".
\code
plotter.setTitle(0, "Visual features error");
plotter.setTitle(1, "Camera velocities");
\endcode
To differentiate the graphics we associate a title to each of them. The first graphic (the one with index 0) will be
designed to draw the evolution of the visual features error, while the second (index 1) will be designed to draw the
camera velocities.
\code
plotter.initGraph(0, 8);
plotter.initGraph(1, 6);
\endcode
Here we initialize the first graphic to be able to plot 8 curves. We recall that we have 4 points, each point has 2
visual features (x and y), that is why there are 8 curves to plot. The second graphic is designed to plot 6 curves
corresponding to the camera velocities (3 translation velocities in m/s and 3 rotation velocities in rad/s).
\code
plotter.setLegend(0, 0, "x1");
plotter.setLegend(0, 1, "y1");
plotter.setLegend(0, 2, "x2");
plotter.setLegend(0, 3, "y2");
plotter.setLegend(0, 4, "x3");
plotter.setLegend(0, 5, "y3");
plotter.setLegend(0, 6, "x4");
plotter.setLegend(0, 7, "y4");
plotter.setLegend(1, 0, "v_x");
plotter.setLegend(1, 1, "v_y");
plotter.setLegend(1, 2, "v_z");
plotter.setLegend(1, 3, "w_x");
plotter.setLegend(1, 4, "w_y");
plotter.setLegend(1, 5, "w_z");
#endif
\endcode
The previous lines allow to associate a legend to each curve.
\code
#ifdef VISP_HAVE_DISPLAY
plotter.plot(0, iter, task.getError());
plotter.plot(1, iter, v);
#endif
\endcode
Once the plotter is initialized, in the servo loop we add at each iteration the corresponding values of the visual
features error \f${\bf e}(t) = {\bf s}-{\bf s}^*\f$, and the camera velocities \f${\bf v}_c\f$.
\code
#ifdef VISP_HAVE_DISPLAY
plotter.saveData(0, "error.dat");
plotter.saveData(1, "vc.dat");
#endif
\endcode
At the end of the servo loop, we save the data that were plotted in two separate files, one for each graphic. The first
line of each text file is the graphic title. Then the coordinates along x,y and z are given in separated columns for
each data.
\code
vpDisplay::getClick(plotter.I);
\endcode
Before exiting the program we wait for a human mouse click in the plotter window.
*/
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