[PCL self study: pclplotter] pclplotter draws data analysis chart

One 、 What is? PCLPlotter

   PCLPoltter Be similar to Matlab Of plot function , It is used to draw analysis diagram for point cloud data , For example, a certain row or column point cloud Z Change diagram of value .PCLPlotter It provides a very direct and simple drawing interface . We can visualize all types of important plots in the library, such as polynomial functions or histograms . When introducing some specific concepts in this chapter , Please read the document carefully , To know the exact method name .
   We learn how to use... Directly from program fragments PCLPlotter Well .

Two 、 The sample program

2.1 Basic drawing process

   From the simplest drawing X,Y Related conic ($y=x^2$) Start .

#include<vector>
#include<iostream>
#include<utility>

#include<pcl/visualization/pcl_plotter.h>
//...

int
main ()
{
    
  // First define a plotter  PCLPlotter
  pcl::visualization::PCLPlotter * plotter = new PCLPlotter ();

  // Then define the polynomial coefficients of the drawing function ,  for example y = x^2. Its polynomial coefficients are 3 individual , Namely 1,0,0, In a defined container , The first 0 One is a constant , The first 1 Yes x The coefficient of , The first 2 Yes x^2 The coefficient of . except x^2 The coefficient is 1, The rest is 0.
  std::vector<double> func1 (3,0);
  func1[2] = 1;

  // With [- 10,10] by X Axis range , With “y = X ^2” Title , Add polynomials to the plotter func1
  plotter->addPlotData (func1, -10, 10, "y = x^2");

  // Display polynomial image 
  plotter->plot ();

  return 0;
}

   After the above code is run, it is as follows ：

   From the above code, we can conclude that PCLPlotter The basic code structure of , It's very simple to use , Be similar to Matlab

...
//1.  Definition 1 individual  plotter. 
pcl::visualization::PCLPlotter *plotter = new PCLPlotter ("My Plotter");

...
//2.  Use addPlotData* () function   Add polynomial coefficient data 
plotter->addPlotData* ();

...
//3.  Set up Plotter Interface properties 
plotter->setWindowSize (900, 600);
plotter->setYTitle ("this is my own function");

...
//4.  display 
plotter->plot ()

   The basic usage framework is introduced , Now we will introduce more details .

2.2 Drawing detail processing

2.2.1 Choose a color scheme for the image

   stay addPlotData*() Function , You can choose to add the desired color to the drawing . But if you don't take the initiative ,Plotter Will automatically color according to the color scheme .
   The default color scheme is vtkColorSeries::SPECTRUM, It contains... In the whole spectrum 7 Two different shades .
   Except for the default , You can also choose vtkColorSeries::WARM, vtkColorSeries::COOL, vtkColorSeries::BLUES, vtkColorSeries::WILD_FLOWER, vtkColorSeries::CITRUS.
   You can go through setColorScheme() Function to change the color scheme . To reflect the effect of the color scheme in all drawings , In calling any addPlotData*() Function before calling this function to take effect .

2.2.2 Select different types of data to enter into the chart

   You can view... In the document addPlotData() Detailed signature of the function . These prototypes basically illustrate their functions .

① Point-Correspondences（ Feature point matching ）
   This is the most basic way to provide input data . Use std::vectorstd::pair; Provide point correspondence , namely (x,y) coordinate . as follows

...
std::vector<std::pair<double, double> > data;
populateData (data);
plotter->addPlotData (data,"cos");
...

② Table ( form )
   The user stores the communication in a text file in the form of a space separated table . This leads to the use of MS Excel Alternative to drawing . Here is a very simple executable file , It carries out MS Excel Plotter The function of .

#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;
}

③ Polynomial and Rational Functions( Polynomial and rational function )
   Polynomials are defined by coefficient vectors , Rational functions are polynomial pairs ( Numerator and denominator pairs ) To define . The following code snippet draws the function y = 1/x The graphic .

...
std::vector<double> func1 (1,0);
func1[0] = 1; // 1
std::vector<double> func2 (2,0);
func1[1] = 1; // x

plotter->addPlotData (std::make_pair (func1, func2),-10, 10, "y = 1/x");
...

④ A custom explicit function( Custom explicit functions )
   The user can specify a custom function ,f Describe the relationship as a callback :Y = f(X)

...
double
identity (double val)
{
    
  return val;
}
...

...
plotter->addPlotData (identity,-10, 10,"identity");
...

2.2.3 Add other attributes and decorations

   Users can add plots of other properties , As the title , Quadrant title , legend , Background color, etc . Need to be in plotter->plot (); Call these functions any time before they are called .

...
plotter->setTitle ("My plot"); //global title
plotter->setXTitle ("degrees");
plotter->setYTitle ("cos");
plotter->setShowLegend (true); //show legends
...
plotter->plot ();
...

2.2.4 Histogram and line chart

  PCLPlotter Provides a very convenient MATLAB Class histogram drawing function (MATLAB Medium hist()). It classifies the raw data according to frequency and draws a bar graph .

...

std::vector<double> freqdata = generateNomalDistData ();

plotter->addHistogramData (freqdata,10); //number of bins are 10

plotter->plot ();
...

2.2.5 Dynamically display graphics as data is added

...

//data and callback defined here
...

plotter->addPlotData (func1, -10, 10, "y = x^2");
plotter->spinOnce (2000);    // Dynamic display frequency  2s Refresh once 

plotter->clearPlots ();
plotter->addPlotData (identity,-10, 10,"identity");
plotter->spinOnce (2000);

plotter->clearPlots ();
plotter->addPlotData (abs,-5, 5,"abs");
plotter->spinOnce (2000);
...

2.3 Demo

  /* \author Kripasindhu Sarkar */
  
  #include<pcl/visualization/pcl_plotter.h>
  
  #include<iostream>
  #include<vector>
  #include<utility>
  #include<cmath> //for std::abs()
  
 using namespace pcl::visualization;
 
 void
 generateData (double *ax, double *acos, double *asin, int numPoints)
 {
    
   double inc = 7.5 / (numPoints - 1);
   for (int i = 0; i < numPoints; ++i)
   {
    
     ax[i] = i*inc;
     acos[i] = std::cos (i * inc);
     asin[i] = sin (i * inc);
   }
 }
 
 //.....................callback functions defining Y= f(X)....................
 double
 step (double val)
 {
    
   if (val > 0)
     return (double) (int) val;
   else
     return (double) ((int) val - 1);
}
 
 double
 identity (double val)
{
    
   return val;
}
//............................................................................
 
 int
 main ()
 {
    
   //defining a plotter
   PCLPlotter *plotter = new PCLPlotter ("My Plotter");
 
   //setting some properties
   plotter->setShowLegend (true);
 
   //generating point correspondances
   int numPoints = 69;
   double ax[100], acos[100], asin[100];
   generateData (ax, acos, asin, numPoints);
 
   //adding plot data
   plotter->addPlotData (ax, acos, numPoints, "cos");
   plotter->addPlotData (ax, asin, numPoints, "sin");
 
   //display for 2 seconds
   plotter->spinOnce (3000);
   plotter->clearPlots ();
   
   
   //...................plotting implicit functions and custom callbacks....................
 
   //make a fixed axis
   plotter->setYRange (-10, 10);
 
   //defining polynomials
   std::vector<double> func1 (1, 0);
   func1[0] = 1; //y = 1
   std::vector<double> func2 (3, 0);
   func2[2] = 1; //y = x^2
 
   plotter->addPlotData (std::make_pair (func1, func2), -10, 10, "y = 1/x^2", 100, vtkChart::POINTS);
   plotter->spinOnce (2000);
 
   plotter->addPlotData (func2, -10, 10, "y = x^2");
   plotter->spinOnce (2000);
 
   //callbacks
   plotter->addPlotData (identity, -10, 10, "identity");
   plotter->spinOnce (2000);
 
   plotter->addPlotData (std::abs, -10, 10, "abs");
   plotter->spinOnce (2000);
 
   plotter->addPlotData (step, -10, 10, "step", 100, vtkChart::POINTS);
   plotter->spinOnce (2000);
 
   plotter->clearPlots ();
 
   //........................A simple animation..............................
   std::vector<double> fsq (3, 0);
   fsq[2] = -100; //y = x^2
   while (!plotter->wasStopped ())
   {
    
     if (fsq[2] == 100) fsq[2] = -100;
     fsq[2]++;
    char str[50];
    sprintf (str, "y = %dx^2", (int) fsq[2]);
    plotter->addPlotData (fsq, -10, 10, str);

    plotter->spinOnce (100);
    plotter->clearPlots ();
  }

  return 1;
}

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【 About bloggers 】
   Stanford rabbit , male , Master of engineering, Tianjin University . Since graduation, I have been engaged in optical three-dimensional imaging and point cloud processing . Because the three-dimensional processing library used in work is the internal library of the company , Not universally applicable , So I learned to open source by myself PCL Library and its related mathematical knowledge for use . I would like to share the self-study process with you .
Bloggers lack of talent and knowledge , Not yet able to guide , If you have any questions, please leave a message in the comments section for everyone to discuss .