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.. _pcl_plotter:
PCLPlotter
==========
PCLPlotter provides a very straightforward and easy interface for plotting graphs. One can visualize all sort of important plots -
from polynomial functions to histograms - inside the library without going to any other software (like MATLAB).
Please go through the `documentation <https://pointclouds.org/documentation/group__visualization.html>`_ when some specific concepts are introduced in this tutorial to know the exact method signatures.
The code for the visualization of a plot are usually as simple as the following snippet.
.. code-block:: cpp
#include<vector>
#include<iostream>
#include<utility>
#include<pcl/visualization/pcl_plotter.h>
//...
int
main ()
{
//defining a plotter
pcl::visualization::PCLPlotter * plotter = new PCLPlotter ();
//defining the polynomial function, y = x^2. Index of x^2 is 1, rest is 0
std::vector<double> func1 (3,0);
func1[2] = 1;
//adding the polynomial func1 to the plotter with [-10, 10] as the range in X axis and "y = x^2" as title
plotter->addPlotData (func1, -10, 10, "y = x^2");
//display the plot, DONE!
plotter->plot ();
return 0;
}
If this program is compiled and run, you will get the following output
.. image:: images/pcl_plotter_x2.png
:width: 640
Basic code structure
--------------------
The following snippet shows the basic structure of code for using PCLPlotter
.. code-block:: cpp
...
//1. define a plotter. Change the colorscheme if you want some different colorscheme in auto-coloring.
pcl::visualization::PCLPlotter *plotter = new PCLPlotter ("My Plotter");
...
//2. add data to be plotted using addPlotData* () functions
plotter->addPlotData* ();
...
//3. add some properties if required
plotter->setWindowSize (900, 600);
plotter->setYTitle ("this is my own function");
...
//4. display the plot
plotter->plot ()
All the subsequent sections will elaborate the above concept in detail.
Auto-coloring
=============
You have the choice to add your own color to the plot in addPlotData*() functions. But if left empty, the plotter will auto-color depending upon a color-scheme.
The default color-scheme is ``vtkColorSeries::SPECTRUM`` which contains 7 different (normal) hues over the entire spectrum. The other values are ``vtkColorSeries::WARM``, ``vtkColorSeries::COOL``, ``vtkColorSeries::BLUES``, ``vtkColorSeries::WILD_FLOWER``, ``vtkColorSeries::CITRUS``.
You can change the colorscheme by *setColorScheme ()* function. To reflect the effect of the color-scheme to all the plots call this function before calling any *addPlotData\*()* functions.
Different types of plot input
==============================
Have a look at the *addPlotData()* functions in the documentation for their detailed signatures. The prototypes pretty much tell about their functionalities. The following subsections contains some of the important input method of the plot.
Point-Correspondences
---------------------
This the most fundamental way of providing input. Provide the point correspondences, that is (x,y) coordinates, for the plot using a std::vector<std::pair> in *addPlotData*
.. code-block:: cpp
...
std::vector<std::pair<double, double> > data;
populateData (data);
plotter->addPlotData (data,"cos");
...
The other ways of input for point correspondences are two arrays of same length denoting the X and Y values of the correspondences.
Table
-----
This is same as the previous one except the fact that the user stores the correspondences in a text file in the form of an space delimited table. This forms a substitute for the plotting using MS Excel. A very simple executable (without decoration) which performs the functionalities of MS Excel Plotter will be the following.
.. code-block:: cpp
#include<pcl/visualization/pcl_plotter.h>
int
main (int argc, char ** argv)
{
pcl::visualization::PCLPlotter * plotter = new PCLPlotter ();
plotter->addPlotData (argv[1]);
plotter->plot ();
return 0;
}
Polynomial and Rational Functions
---------------------------------
Polynomial are defined in terms of vector of coefficients and Rational functions are defined in terms of pair of polynomial (pair of numerator and denominator) . See the definition in the documentation. The following snippet plots the function y = 1/x
.. code-block:: cpp
...
std::vector<double> func1 (1,0);
func1[0] = 1;
std::vector<double> func2 (2,0);
func1[1] = 1;
plotter->addPlotData (std::make_pair (func1, func2),-10, 10, "y = 1/x");
...
A custom explicit function
--------------------------
User can specify a custom function, *f* depicting the relation: *Y = f(X)* in the form of a callback
.. code-block:: cpp
...
double
identity (double val)
{
return val;
}
...
...
plotter->addPlotData (identity,-10, 10,"identity");
...
Adding other properties and decorations
=======================================
One can add other properties of the plot like *title*, *legends*, *background colours* etc. You can call these functions at any time before any display (*plot()/spin\*()*) function call.
.. code-block:: cpp
...
plotter->setTitle ("My plot"); //global title
plotter->setXTitle ("degrees");
plotter->setYTitle ("cos");
plotter->setShowLegend (true); //show legends
...
plotter->plot ();
...
Other Functionalities
=====================
PCLPlotter provides few other important functionalities other than plotting given a well defined plots and correspondences. These includes a histogram plotting functions and all functionalities of the legacy class PCLHistogramVisualizer.
'Plotting' Histogram
--------------------
PCLPlotter provides a very convenient MATLAB like histogram plotting function (`hist() <http://www.mathworks.fr/fr/help/matlab/ref/hist.html>`_ in MATLAB). It takes raw data and bins them according to their frequency and plot them as bar chart.
.. code-block:: cpp
...
std::vector<double> freqdata = generateNomalDistData ();
plotter->addHistogramData (freqdata,10); //number of bins are 10
plotter->plot ();
...
PCLHistogramVisualizer functions
---------------------------------
All functionalities of PCLHistogramVisualizer has been rewritten and added to the plotter with their signature retained. See the documentation for method details.
Display
=======
To display all the plots added use the simple function - *plot()*. PCLPlotter is also provided with the legacy *spin\*()* functions which can be used for animations or updating the plots with time.
The following snippet shows the functionality.
.. code-block:: cpp
...
//data and callback defined here
...
plotter->addPlotData (func1, -10, 10, "y = x^2");
plotter->spinOnce (2000); //display the plot for 2 seconds
plotter->clearPlots ();
plotter->addPlotData (identity,-10, 10,"identity");
plotter->spinOnce (2000);
plotter->clearPlots ();
plotter->addPlotData (abs,-5, 5,"abs");
plotter->spinOnce (2000);
...
Demo
=====
Following is a complete example depicting many usage of the Plotter. Copy it into a file named ``pcl_plotter_demo.cpp``.
.. literalinclude:: sources/pcl_plotter/pcl_plotter_demo.cpp
:language: cpp
:linenos:
Compiling and running the program
---------------------------------
Add the following lines to your `CMakeLists.txt` file:
.. literalinclude:: sources/pcl_plotter/CMakeLists.txt
:language: cmake
:linenos:
Compile and run the code by the following commands ::
$ cmake .
$ make
$ ./pcl_plotter_demo
Video
-----
The following video shows the the output of the demo.
.. raw:: html
<iframe width="480" height="270" src="https://www.youtube.com/embed/2Xgd67nkwzs" frameborder="0" allowfullscreen></iframe>
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