Visual Servoing Platform  version 3.0.0
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vpMomentGravityCenter Class Reference
core: Core module » Tools » Image moments

#include <visp3/core/vpMomentGravityCenter.h>

+ Inheritance diagram for vpMomentGravityCenter:

Public Member Functions

 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
 
const vpMomentObject & getObject () const
 
void linkTo (vpMomentDatabase &moments)
 
void update (vpMomentObject &object)
 

Protected Member Functions

vpMomentDatabase & getMoments () const
 

Protected Attributes

std::vector< double > values
 

Friends

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
vpPoint p;
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)
vec_p.push_back(p);
p.set_x(+0.3); p.set_y(0.1); // coordinates in meters in the image plane (vertex 2)
vec_p.push_back(p);
p.set_x(+0.2); p.set_y(-0.1); // coordinates in meters in the image plane (vertex 3)
vec_p.push_back(p);
p.set_x(-0.2); p.set_y(-0.15); // coordinates in meters in the image plane (vertex 4)
vec_p.push_back(p);
p.set_x(-0.2); p.set_y(0.1); // close the contour (vertex 5 = vertex 1)
vec_p.push_back(p);
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
Xg=0.0166667, Yg=-0.00833333

Definition at line 109 of file vpMomentGravityCenter.h.

Constructor & Destructor Documentation

vpMomentGravityCenter::vpMomentGravityCenter ( )

Default constructor.

Definition at line 51 of file vpMomentGravityCenter.cpp.

References vpMoment::values.

Member Function Documentation

void vpMomentGravityCenter::compute ( )
virtual

Computes the two gravity center coordinates commonly called $x_g$ and $y_g$.

Implements vpMoment.

Reimplemented in vpMomentGravityCenterNormalized.

Definition at line 43 of file vpMomentGravityCenter.cpp.

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

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

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

Returns a vector of the two gravity center coordinates.

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

Definition at line 59 of file vpMomentGravityCenter.cpp.

References vpMoment::values.

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

vpMomentDatabase& vpMoment::getMoments ( ) const
inlineprotectedinherited

Returns the linked moment database.

Returns
the moment database

Definition at line 119 of file vpMoment.h.

Referenced by vpMomentArea::compute(), vpMomentGravityCenterNormalized::compute(), vpMomentCentered::compute(), vpMomentAreaNormalized::compute(), vpMomentCInvariant::compute(), vpMomentAlpha::compute(), vpMomentArea::printDependencies(), vpMomentGravityCenterNormalized::printDependencies(), vpMomentCentered::printDependencies(), vpMomentAreaNormalized::printDependencies(), and vpMomentAlpha::printDependencies().

const vpMomentObject& vpMoment::getObject ( ) const
inlineinherited

Definition at line 143 of file vpMoment.h.

Referenced by vpMomentArea::compute(), vpMomentCentered::compute(), compute(), vpMomentAreaNormalized::compute(), vpMomentCInvariant::compute(), vpFeatureMomentArea::compute_interaction(), vpFeatureMomentBasic::compute_interaction(), vpFeatureMomentCentered::compute_interaction(), vpFeatureMomentAlpha::compute_interaction(), vpFeatureMomentAreaNormalized::compute_interaction(), vpFeatureMomentCInvariant::compute_interaction(), vpFeatureMomentGravityCenter::compute_interaction(), vpFeatureMomentGravityCenterNormalized::compute_interaction(), vpMomentBasic::get(), vpMomentCentered::get(), vpFeatureMomentBasic::interaction(), vpFeatureMomentCentered::interaction(), vpMomentArea::printDependencies(), vpMomentBasic::printDependencies(), vpMomentCentered::printDependencies(), printDependencies(), vpMomentAreaNormalized::printDependencies(), vpMomentCentered::printWithIndices(), and vpMomentCentered::set().

double vpMomentGravityCenter::getXg ( ) const
inline

Shortcut function to retrieve $x_g$.

Returns
The first gravity center coordinate.

Definition at line 119 of file vpMomentGravityCenter.h.

Referenced by vpFeatureMomentArea::compute_interaction(), vpFeatureMomentCentered::compute_interaction(), vpFeatureMomentAlpha::compute_interaction(), vpFeatureMomentAreaNormalized::compute_interaction(), vpFeatureMomentGravityCenter::compute_interaction(), vpFeatureMomentGravityCenterNormalized::compute_interaction(), and vpMomentCentered::printDependencies().

double vpMomentGravityCenter::getYg ( ) const
inline

Shortcut function to retrieve $y_g$.

Returns
The second gravity center coordinate.

Definition at line 124 of file vpMomentGravityCenter.h.

Referenced by vpFeatureMomentArea::compute_interaction(), vpFeatureMomentCentered::compute_interaction(), vpFeatureMomentAlpha::compute_interaction(), vpFeatureMomentAreaNormalized::compute_interaction(), vpFeatureMomentGravityCenter::compute_interaction(), vpFeatureMomentGravityCenterNormalized::compute_interaction(), and vpMomentCentered::printDependencies().

void vpMoment::linkTo ( vpMomentDatabase &  data_base)
inherited

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.

Attention
Two moments of the same class cannot be stored in the same database
#include <visp3/core/vpMomentObject.h>
#include <visp3/core/vpPoint.h>
#include <visp3/core/vpMomentGravityCenter.h>
#include <visp3/core/vpMomentDatabase.h>
#include <visp3/core/vpMomentCentered.h>
int main()
{
vpPoint p;
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)
vpMomentObject obj(2);
obj.setType(vpMomentObject::DISCRETE); // Discrete mode.
obj.fromVector(vec_p); // Init the dense object with the polygon
vpMomentDatabase db;
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;
}
Parameters
data_base: database of moment primitives.

Definition at line 99 of file vpMoment.cpp.

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

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

const char* vpMomentGravityCenter::name ( ) const
inlinevirtual

The class's string name.

Implements vpMoment.

Reimplemented in vpMomentGravityCenterNormalized.

Definition at line 128 of file vpMomentGravityCenter.h.

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

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().

void vpMoment::update ( vpMomentObject &  moment_object)
inherited

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

Parameters
moment_object: object descriptor of the current camera vision.

Definition at line 116 of file vpMoment.cpp.

Friends And Related Function Documentation

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

Outputs the moment's values to a stream.

Definition at line 66 of file vpMomentGravityCenter.cpp.

Member Data Documentation

std::vector<double> vpMoment::values
protectedinherited

Definition at line 114 of file vpMoment.h.

Referenced by vpMomentArea::compute(), vpMomentGravityCenterNormalized::compute(), vpMomentCentered::compute(), compute(), vpMomentAreaNormalized::compute(), vpMomentCInvariant::compute(), vpMomentAlpha::compute(), vpMomentCentered::get(), get(), vpMomentCInvariant::getMomentVector(), vpMomentCentered::set(), vpMomentAlpha::vpMomentAlpha(), vpMomentArea::vpMomentArea(), vpMomentAreaNormalized::vpMomentAreaNormalized(), vpMomentCInvariant::vpMomentCInvariant(), and vpMomentGravityCenter().