Visual Servoing Platform  version 3.1.0
vpMoment Class Referenceabstract

#include <visp3/core/vpMoment.h>

+ Inheritance diagram for vpMoment:

Public Member Functions

 vpMoment ()
virtual ~vpMoment ()
Inherited functionalities from vpMoment
virtual void compute ()=0
const vpMomentObjectgetObject () const
const std::vector< double > & get () const
void linkTo (vpMomentDatabase &moments)
virtual const char * name () const =0
virtual void printDependencies (std::ostream &os) const
void update (vpMomentObject &object)

Protected Member Functions

vpMomentDatabasegetMoments () const

Protected Attributes

std::vector< double > values


VISP_EXPORT std::ostream & operator<< (std::ostream &os, const vpMoment &m)

Detailed Description

This class defines shared methods/attributes for 2D moments.

All moments or combination of moments in the moments module are based on this class. A moment uses a vpMomentObject object to access all useful information. Moment values are obtained by a 4-step process common for all moment types:

  • Declaration.
    vpMoment moment;
  • Update with object.
  • Compute the moment value
  • Access the values:
    std::vector<double> values = moment.get();

A moment may also be linked to a vpMomentDatabase. Moments linked to a database are able to access each others values. Some moments can be computed only if they are linked to a a database containing their dependencies. Linking to a database is done using the vpMoment::linkTo(...) method.

There are no constraints about format of the array returned by vpMoment::get(); any implementation is fine.

Each moment must have a string name by implementing the char* vpMoment::name() method which allows to identify the moment in the database. Each moment must also implement a compute method describing how to obtain its values from the object.

Order of moment computation DOES matter: when you compute a moment using vpMoment::compute(), all moment dependencies must be computed. We recall that implemented moments are:

Definition at line 110 of file vpMoment.h.

Constructor & Destructor Documentation

◆ vpMoment()

vpMoment::vpMoment ( )

Default constructor

Definition at line 51 of file vpMoment.cpp.

◆ ~vpMoment()

virtual vpMoment::~vpMoment ( )

Virtual destructor.

Definition at line 145 of file vpMoment.h.

Member Function Documentation

◆ compute()

◆ get()

◆ getMoments()

◆ getObject()

◆ 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 name().

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

◆ name()

virtual const char* vpMoment::name ( ) const
pure virtual

◆ printDependencies()

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

Prints values of all dependent moments required to calculate a specific vpMoment. Not made pure to maintain compatibility Recommended : Types inheriting from vpMoment should implement this function

Reimplemented in vpMomentAlpha, vpMomentAreaNormalized, vpMomentGravityCenter, vpMomentCentered, vpMomentBasic, vpMomentGravityCenterNormalized, and vpMomentArea.

Definition at line 135 of file vpMoment.cpp.

Referenced by vpMomentAlpha::is_symmetric(), vpMomentArea::name(), vpMomentBasic::name(), vpMomentCentered::name(), vpMomentGravityCenter::name(), and vpMomentAreaNormalized::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 vpMoment m 

Prints the moment contents to a stream

os: a std::stream.
m: a moment instance.

Definition at line 122 of file vpMoment.cpp.

Referenced by vpMomentCInvariant::getMomentVector(), vpMomentAlpha::is_symmetric(), vpMomentArea::name(), vpMomentBasic::name(), vpMomentCentered::name(), vpMomentGravityCenter::name(), and vpMomentAreaNormalized::name().

Member Data Documentation

◆ values