#include <visp3/core/vpMomentAlpha.h>

Inheritance diagram for vpMomentAlpha:

Public Member Functions
	vpMomentAlpha ()

	vpMomentAlpha (std::vector< double > &ref, double alphaRef)

virtual	~vpMomentAlpha ()

void	compute ()

double	get () const

const char *	name () const

bool	is_ref () const

bool	is_symmetric () const

void	printDependencies (std::ostream &os) const

Inherited functionalities from vpMoment
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 vpMomentAlpha &v)

Detailed Description

This class defines the orientation of the object inside the plane parallel to the object.

In general the value of the moment is computed in $[-\pi/2 .. \pi/2]$ interval by the formula $\alpha = \frac{1}{2} arctan(\frac{2\mu_{11}}{\mu_{20}-\mu_{02}})$ .

To obtain a $[-\pi .. \pi]$ precision for non symetric object, you have to specify a reference information. This reference information is an alpha computed using the previous formula in $[-\pi/2 .. \pi/2]$ . Obtaining this precision comes from third-order centered moments and this reference information.

Therefore there are two modes for vpMomentAlpha and one constructor per mode:

Reference mode (using the empty constructor vpMomentAlpha()): The vpMomentAlpha doesn't need any additionnal information, it will compute its values from available moments in $[-\pi/2 .. \pi/2]$ .
Relative mode (using non-empty constructor vpMomentAlpha(std::vector<double>&, double)): The vpMomentAlpha is computed in $[-\pi .. \pi]$ from the available moments and the reference information. By knowing the reference, it may distinguish in-plane rotations of $\alpha$ from rotations of $\alpha + \pi$ .

The following code demonstrates a calculation of a reference alpha and then uses this alpha to estimate the orientation of the same object after performing a 180 degrees rotation. Therefore the first and second alpha should have opposite values.

#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>
#include <visp3/core/vpMomentAlpha.h>
#include <iostream>
#include <vector>
#include <algorithm>
//generic function for printing
void print (double i) { std::cout << i << "\t";}
int main()
{
  vpPoint p;
  std::vector<vpPoint> vec_p; // 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)
  vec_p.push_back(p);
  p.set_x(2); p.set_y(2); // coordinates in meters in the image plane (vertex 2)
  vec_p.push_back(p);
  p.set_x(-3); p.set_y(0); // coordinates in meters in the image plane (vertex 3)
  vec_p.push_back(p);
  p.set_x(-3); p.set_y(-1); // coordinates in meters in the image plane (vertex 4)
  vec_p.push_back(p);
  vpMomentObject objRef(3); // Reference object. Must be of order 3
                            // because we will need the 3rd order
                            // centered moments
  objRef.setType(vpMomentObject::DENSE_POLYGON); // object is the inner part of a polygon
  objRef.fromVector(vec_p); // Init the dense object with the polygon
  vpMomentDatabase dbRef; //reference database
  vpMomentGravityCenter gRef; // declaration of gravity center
  vpMomentCentered mcRef; //  centered moments
  vpMomentAlpha alphaRef; //declare alpha as reference
  gRef.linkTo(dbRef); //add gravity center to database
  mcRef.linkTo(dbRef); //add centered moments
  alphaRef.linkTo(dbRef); //add alpha depending on centered moments
  dbRef.updateAll(objRef); // All of the moments must be updated, not just alpha
  gRef.compute(); // compute the moment
  mcRef.compute(); //compute centered moments AFTER gravity center
  alphaRef.compute(); //compute alpha AFTER centered moments.
  //the order of values in the vector must be as follows:
  //mu30 mu21 mu12 mu03
  std::vector<double> mu3ref(4);
  mu3ref[0] = mcRef.get(3,0);
  mu3ref[1] = mcRef.get(2,1);
  mu3ref[2] = mcRef.get(1,2);
  mu3ref[3] = mcRef.get(0,3);
  std::cout << "--- Reference object ---" << std::endl;
  std::cout << "alphaRef=" << alphaRef << std::endl << "mu3="; // print reference alpha
  std::for_each (mu3ref.begin(), mu3ref.end(),print);
  std::cout << std::endl;
  vec_p.clear();
  p.set_x(-3); p.set_y(1); // coordinates in meters in the image plane (vertex 4)
  vec_p.push_back(p);
  p.set_x(-3); p.set_y(0); // coordinates in meters in the image plane (vertex 3)
  vec_p.push_back(p);
  p.set_x(2); p.set_y(-2); // coordinates in meters in the image plane (vertex 2)
  vec_p.push_back(p);
  p.set_x(1); p.set_y(-1); // coordinates in meters in the image plane (vertex 1)
  vec_p.push_back(p);
  vpMomentObject obj(3); // second object. Order 3 is also required
                         // because of the Alpha will compare
                         // third-order centered moments to given reference.
  obj.setType(vpMomentObject::DENSE_POLYGON); // object is the inner part of a polygon
  obj.fromVector(vec_p); // Init the dense object with the polygon
  vpMomentDatabase db; // database
  vpMomentGravityCenter g; // declaration of gravity center
  vpMomentCentered mc; // mc containts centered moments
  vpMomentAlpha alpha(mu3ref,alphaRef.get()); //declare alpha as relative to a reference
  g.linkTo(db); //add gravity center to database
  mc.linkTo(db); //add centered moments
  alpha.linkTo(db); //add alpha depending on centered moments
  db.updateAll(obj); // All of the moments must be updated
  g.compute(); // compute the moment
  mc.compute(); //compute centered moments AFTER gravity center
  alpha.compute(); //compute alpha AFTER centered moments.
  std::cout << "--- current object ---" << std::endl;
  std::cout << "alpha=" << alpha.get() << std::endl;
  return 0;
}

This program outputs:

--- Reference object ---
alphaRef=0.441601
mu3=1.80552 0.921882    0.385828    0.122449
--- current object ---
alpha=-0.441601

Shortcuts for quickly getting those references exist in vpMomentCommon.

This moment depends on vpMomentCentered.

Definition at line 196 of file vpMomentAlpha.h.

Constructor & Destructor Documentation

vpMomentAlpha::vpMomentAlpha ( )

Empty constructor. Initializes alpha moment as a reference alpha with a value in $[-\pi/2..\pi/2]$ . A default-constructed alpha moment may be used as a reference information for other alphas. A reference alpha is a class harbouring an alpha value computed for a $[-\pi/2..\pi/2]$ portion of the circle.

Definition at line 48 of file vpMomentAlpha.cpp.

References vpMoment::values.

vpMomentAlpha::vpMomentAlpha	(	std::vector< double > &	ref_,
		double	alpha_ref
	)

Common constructor. Initializes alpha moment as a non-reference alpha with a value computed in $[-\pi..\pi]$ .

Parameters

ref_	: vector of 3rd order centered moments corresponding to the reference alpha in the following order: $\mu_{30},\mu_{21},\mu_{12},\mu_{03}$ .
alpha_ref	: value of the reference alpha.

Definition at line 58 of file vpMomentAlpha.cpp.

References vpMoment::values.

virtual vpMomentAlpha::~vpMomentAlpha ( )

inlinevirtual

Definition at line 206 of file vpMomentAlpha.h.

Member Function Documentation

void vpMomentAlpha::compute ( )

virtual

Compute the value of the alpha-moment. Depends on vpMomentCentered.

Implements vpMoment.

Definition at line 72 of file vpMomentAlpha.cpp.

References vpMath::comb(), vpMomentCentered::get(), vpMomentDatabase::get(), vpMoment::getMoments(), vpException::notInitialized, and vpMoment::values.

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

double vpMomentAlpha::get ( ) const

inline

Retrieve the orientation of the object as a single double value.

Definition at line 212 of file vpMomentAlpha.h.

Referenced by vpMomentCommon::getAlpha().

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(), compute(), vpMomentArea::printDependencies(), vpMomentGravityCenterNormalized::printDependencies(), vpMomentCentered::printDependencies(), vpMomentAreaNormalized::printDependencies(), and printDependencies().

const vpMomentObject& vpMoment::getObject ( ) const

inlineinherited

Definition at line 145 of file vpMoment.h.

bool vpMomentAlpha::is_ref ( ) const

inline

Definition at line 218 of file vpMomentAlpha.h.

bool vpMomentAlpha::is_symmetric ( ) const

inline

Definition at line 226 of file vpMomentAlpha.h.

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* vpMomentAlpha::name ( ) const

inlinevirtual

Moment name.

Implements vpMoment.

Definition at line 216 of file vpMomentAlpha.h.

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

virtual

Prints the dependencies of alpha, namely centered moments mu11, mu20 ad mu02

Reimplemented from vpMoment.

Definition at line 163 of file vpMomentAlpha.cpp.

References vpMomentCentered::get(), vpMomentDatabase::get(), vpMoment::getMoments(), and vpException::notInitialized.

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 vpMomentAlpha &	v
	)

friend

Prints the value of the major-axis orientation in degrees and rad

Definition at line 154 of file vpMomentAlpha.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(), vpMomentGravityCenter::compute(), vpMomentAreaNormalized::compute(), vpMomentCInvariant::compute(), compute(), vpMomentCentered::get(), vpMomentGravityCenter::get(), vpMomentCInvariant::getMomentVector(), vpMomentCentered::set(), vpMomentAlpha(), vpMomentArea::vpMomentArea(), vpMomentAreaNormalized::vpMomentAreaNormalized(), vpMomentCInvariant::vpMomentCInvariant(), and vpMomentGravityCenter::vpMomentGravityCenter().

Public Member Functions

Protected Member Functions

Protected Attributes

Friends

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation

Friends And Related Function Documentation

Member Data Documentation