Visual Servoing Platform  version 3.1.0
vpMomentGravityCenter Class Reference

#include <visp3/core/vpMomentGravityCenter.h>

+ Inheritance diagram for vpMomentGravityCenter:

Public Member Functions

 vpMomentGravityCenter ()
virtual ~vpMomentGravityCenter ()
Inherited functionalities from vpMomentGravityCenter
void compute ()
const std::vector< double > & get () const
double getXg () const
double getYg () const
const char * name () const
void printDependencies (std::ostream &os) const
Inherited functionalities from vpMoment
const vpMomentObjectgetObject () const
void linkTo (vpMomentDatabase &moments)
void update (vpMomentObject &object)

Protected Member Functions

vpMomentDatabasegetMoments () const

Protected Attributes

std::vector< double > values


VISP_EXPORT std::ostream & operator<< (std::ostream &os, const vpMomentGravityCenter &v)

Detailed Description

Class describing 2D gravity center moment.

This moment can be computed from scratch (no need to compute any different moments before computing this). It gives access to both coordinates of the gravity center $x_g$ and $y_g$.

These coordinates are defined as follows: $x_g = \frac{m_{01}}{m_{00}} $, $y_g = \frac{m_{10}}{m_{00}} $

#include <visp3/core/vpMomentObject.h>
#include <visp3/core/vpPoint.h>
#include <visp3/core/vpMomentGravityCenter.h>
#include <iostream>
int main()
// Define the contour of an object by a 5 clockwise vertices on a plane
std::vector<vpPoint> vec_p; // vector that contains the vertices of the contour polygon
p.set_x(-0.2); p.set_y(0.1); // coordinates in meters in the image plane (vertex 1)
p.set_x(+0.3); p.set_y(0.1); // coordinates in meters in the image plane (vertex 2)
p.set_x(+0.2); p.set_y(-0.1); // coordinates in meters in the image plane (vertex 3)
p.set_x(-0.2); p.set_y(-0.15); // coordinates in meters in the image plane (vertex 4)
p.set_x(-0.2); p.set_y(0.1); // close the contour (vertex 5 = vertex 1)
vpMomentObject obj(1); // Create an image moment object with 1 as
// maximum order (because only m00,m01,m10
// are needed to compute the gravity center primitive.
obj.setType(vpMomentObject::DENSE_POLYGON); // The object is defined by a countour polygon
obj.fromVector(vec_p); // Init the dense object with the polygon
vpMomentGravityCenter g; // declaration of gravity center
g.update(obj); // specify the object
g.compute(); // compute the moment
std::cout << "Xg=" << g.getXg() << std::endl; // access to Xg
std::cout << "Yg=" << g.getYg() << std::endl; // access to Yg
std::cout << g << std:: endl; // print gravity center
return 0;

This example produces the following results:

Xg=0.0166667, Yg=-0.00833333

Definition at line 113 of file vpMomentGravityCenter.h.

Constructor & Destructor Documentation

◆ vpMomentGravityCenter()

vpMomentGravityCenter::vpMomentGravityCenter ( )

Default constructor.

Definition at line 54 of file vpMomentGravityCenter.cpp.

References vpMoment::values.

◆ ~vpMomentGravityCenter()

virtual vpMomentGravityCenter::~vpMomentGravityCenter ( )

Definition at line 117 of file vpMomentGravityCenter.h.

References vpMoment::compute().

Member Function Documentation

◆ compute()

void vpMomentGravityCenter::compute ( )

◆ get()

const std::vector< double > & vpMomentGravityCenter::get ( ) const

Returns a vector of the two gravity center coordinates.

Coordinates in the following moment: $(x_g,y_g)$.

Definition at line 60 of file vpMomentGravityCenter.cpp.

References vpMoment::values.

Referenced by vpMomentGravityCenterNormalized::compute(), vpMomentCentered::compute(), vpFeatureMomentCentered::compute_interaction(), and vpMomentGravityCenterNormalized::printDependencies().

◆ getMoments()

◆ getObject()

◆ getXg()

◆ getYg()

◆ linkTo()

void vpMoment::linkTo ( vpMomentDatabase data_base)

Links the moment to a database of moment primitives. If the moment depends on other moments, these moments must be linked to the same database.

Two moments of the same class cannot be stored in the same database
#include <visp3/core/vpMomentCentered.h>
#include <visp3/core/vpMomentDatabase.h>
#include <visp3/core/vpMomentGravityCenter.h>
#include <visp3/core/vpMomentObject.h>
#include <visp3/core/vpPoint.h>
int main()
std::vector<vpPoint> vec_p;
p.set_x(1); p.set_y(1); // coordinates in meters in the image plane (vertex 1)
vec_p.push_back(p); p.set_x(2); p.set_y(2); // coordinates in meters in the image plane (vertex 2)
obj.setType(vpMomentObject::DISCRETE); // Discrete mode.
obj.fromVector(vec_p); // Init the dense object with the polygon
vpMomentGravityCenter G; // declaration of gravity center
vpMomentCentered mc; // mc containts centered moments
G.linkTo(db); //add gravity center to database
mc.linkTo(db); //centered moments depend on gravity, add them to the
//database to grant access
G.update(obj); // specify the object for gravity center
mc.update(obj); // and for centered moments
G.compute(); // compute the moment
mc.compute(); //compute centered moments AFTER gravity center
return 0;
data_base: database of moment primitives.

Definition at line 98 of file vpMoment.cpp.

References vpException::memoryAllocationError, and vpMoment::name().

Referenced by vpMomentCommon::getAlpha(), vpMomentCommon::getMu3(), vpMomentCommon::getSurface(), and vpMomentCommon::vpMomentCommon().

◆ name()

const char* vpMomentGravityCenter::name ( ) const

The class's string name.

Implements vpMoment.

Reimplemented in vpMomentGravityCenterNormalized.

Definition at line 136 of file vpMomentGravityCenter.h.

References vpMoment::operator<<, and vpMoment::printDependencies().

◆ printDependencies()

void vpMomentGravityCenter::printDependencies ( std::ostream &  os) const

Prints its dependencies Basic moments m10, m01 and m00 from vpMomentObject

Reimplemented from vpMoment.

Reimplemented in vpMomentGravityCenterNormalized.

Definition at line 76 of file vpMomentGravityCenter.cpp.

References vpMomentObject::get(), and vpMoment::getObject().

Referenced by vpMomentGravityCenterNormalized::name().

◆ update()

void vpMoment::update ( vpMomentObject moment_object)

Updates the moment with the current object. This does not compute any values.

moment_object: object descriptor of the current camera vision.

Definition at line 115 of file vpMoment.cpp.

Friends And Related Function Documentation

◆ operator<<

VISP_EXPORT std::ostream& operator<< ( std::ostream &  os,
const vpMomentGravityCenter v 

Outputs the moment's values to a stream.

Definition at line 65 of file vpMomentGravityCenter.cpp.

Referenced by vpMomentGravityCenterNormalized::name().

Member Data Documentation

◆ values