Visual Servoing Platform  version 3.2.0 under development (2018-08-20)
vpMomentCommon Class Reference

#include <visp3/core/vpMomentCommon.h>

+ Inheritance diagram for vpMomentCommon:

Public Member Functions

 vpMomentCommon (double dstSurface, const std::vector< double > &ref, double refAlpha, double dstZ=1.0, bool flg_sxsyfromnormalized=false)
virtual ~vpMomentCommon ()
void updateAll (vpMomentObject &object)
Inherited functionalities from vpMomentDatabase
const vpMomentget (const char *type, bool &found) const
vpMomentget_first ()

Static Public Member Functions

static double getAlpha (vpMomentObject &object)
static std::vector< double > getMu3 (vpMomentObject &object)
static double getSurface (vpMomentObject &object)

Detailed Description

This class initializes and allows access to commonly used moments.

It is a vpMomentDatabase filled with the following moments:

There is no need to do the linkTo operations manually nor is it necessary to care about the order of moment computation.

This class carries an vpMomentCommon::updateAll() method capable of updating AND computing moments from an object (see 4-step process in vpMoment). The moments computed by this class are classical moments used in moment-based visual servoing. For more information see [40].

To initialize this moment set the user needs to compute the following things:

  • the Mu3 value set: set of third-order centered moments computed for a reference object. ( $\mu_{ij}$ with $i+j = 3$ ). These values allow the system to save the reference angular position and to perform planar rotations of more than 180 degrees if needed.
  • the destination depth.
  • the surface of the destination object in the end of the visual servoing process.
  • the reference alpha: angular position of the object used to obtain the Mu3 set.

Shortcuts for each of these prerequisites are provided by this class except depth (methods vpMomentCommon::getMu3(), vpMomentCommon::getSurface(), vpMomentCommon::getAlpha()).

Make sure your object is at least of order 5 when using this pre-filled database.
manServoMomentsSimple.cpp, servoMomentImage.cpp, servoMomentPoints.cpp, and servoMomentPolygon.cpp.

Definition at line 104 of file vpMomentCommon.h.

Constructor & Destructor Documentation

vpMomentCommon::vpMomentCommon ( double  dstSurface,
const std::vector< double > &  ref,
double  refAlpha,
double  dstZ = 1.0,
bool  flg_sxsyfromnormalized = false 

Default constructor. Initializes the common database with the following moments: basic, gravity,centered,centered+normalized,normalized gravity,normalized surface, scale-plane-rotation-translation invariant, alpha, symmetric invariant.

dstSurface: destination surface. You may use vpMomentCommon::getSurface().
ref: reference 3rd order moments (see vpMomentAlpha). You may use vpMomentCommon::getMu3().
refAlpha: reference alpha (see vpMomentAlpha). You may use vpMomentCommon::getAlpha().
dstZ: destination depth.
flg_sxsyfromnormalized: flag to enable calculation of sx,sy from normalized moments.

Definition at line 54 of file vpMomentCommon.cpp.

References vpMoment::linkTo().

vpMomentCommon::~vpMomentCommon ( )

Definition at line 226 of file vpMomentCommon.cpp.

Member Function Documentation

vpMoment& vpMomentDatabase::get_first ( )

Get the first element in the database. May be useful in case an unnamed object is present but is the only element in the database.

the first element in the database.

Definition at line 154 of file vpMomentDatabase.h.

double vpMomentCommon::getAlpha ( vpMomentObject object)
std::vector< double > vpMomentCommon::getMu3 ( vpMomentObject object)

Gets the reference 3rd order moments of an object.

object: Moment object.
manServoMomentsSimple.cpp, servoMomentImage.cpp, servoMomentPoints.cpp, and servoMomentPolygon.cpp.

Definition at line 199 of file vpMomentCommon.cpp.

References vpMomentCentered::compute(), vpMomentGravityCenter::compute(), vpMomentCentered::get(), vpMoment::linkTo(), and vpMomentDatabase::updateAll().

double vpMomentCommon::getSurface ( vpMomentObject object)
void vpMomentCommon::updateAll ( vpMomentObject object)

Updates all moments in the database with the object and computes all their values. This is possible because this particular database knows the link between the moments it contains. The order of computation is as follows: vpMomentGravityCenter,vpMomentCentered,vpMomentAlpha,vpMomentCInvariant,vpMomentSInvariant,vpMomentAreaNormalized,vpMomentGravityCenterNormalized

object: Moment object.

Example of using a preconfigured database to compute one of the C-invariants:

#include <iostream>
#include <visp3/core/vpMomentCInvariant.h>
#include <visp3/core/vpMomentCommon.h>
#include <visp3/core/vpMomentObject.h>
#include <visp3/core/vpPoint.h>
int main()
// Define two discrete points
std::vector<vpPoint> vec_p; // std::vector that contains the vertices of the contour polygon
p.set_x(1); p.set_y(1); // coordinates in meters in the image plane (vertex 1)
p.set_x(2); p.set_y(2); // coordinates in meters in the image plane (vertex 2)
p.set_y(0); // coordinates in meters in the image plane (vertex 3)
p.set_y(1); // coordinates in meters in the image plane (vertex 4)
vpMomentObject obj(5); // Object initialized up to order 5 to handle
// all computations required by vpMomentCInvariant
obj.setType(vpMomentObject::DENSE_POLYGON); // object is the inner part of a polygon
obj.fromstd::vector(vec_p); // Init the discrete object with two points
//initialisation with default values
bool success;
db.updateAll(obj); // Update AND compute all moments
//get C-invariant
vpMomentCInvariant& C = static_cast<vpMomentCInvariant&>(db.get("vpMomentCInvariant",success));
if(success) {
std::cout << C.get(0) << std:: std::endl;
} else
std::cout << "vpMomentCInvariant not found." << std::endl;
return 0;

Reimplemented from vpMomentDatabase.

servoMomentImage.cpp, servoMomentPoints.cpp, and servoMomentPolygon.cpp.

Definition at line 126 of file vpMomentCommon.cpp.

References vpMomentArea::compute(), vpMomentGravityCenterNormalized::compute(), vpMomentCentered::compute(), vpMomentGravityCenter::compute(), vpMomentAreaNormalized::compute(), vpMomentCInvariant::compute(), vpMomentAlpha::compute(), and vpMomentDatabase::updateAll().