#include <vpMomentAlpha.h>

Inheritance diagram for vpMomentAlpha:

Public Member Functions
	vpMomentAlpha ()

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

void	compute ()

double	get ()

const char *	name ()

vpMomentObject &	getObject ()

void	linkTo (vpMomentDatabase &moments)

void	update (vpMomentObject &object)

Protected Member Functions
vpMomentDatabase &	getMoments ()

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.

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

To obtain the $[-\pi .. \pi]$ precision, you have to specify reference information. This reference information describes an object with 0 rad orientation or at least an orientation between $-\pi/2$ and $\pi/2$ rad. The nature of this information are third-order centered moments and a reference value of alpha. Reference centered moments are obtained with vpMomentCentered and reference alpha is obtained with vpMomentAlpha using the reference constructor.

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

Reference mode (using the empty constructor): The vpMomentAlpha doesn't need any additionnal information, it will compute its values from a reference object.
Relative mode (using non-empty constructor): The vpMomentAlpha is computed relative a reference alpha. 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 <visp/vpMomentObject.h>
#include <visp/vpPoint.h>
#include <visp/vpMomentGravityCenter.h>
#include <visp/vpMomentDatabase.h>
#include <visp/vpMomentCentered.h>
#include <visp/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 198 of file vpMomentAlpha.h.

Constructor & Destructor Documentation

vpMomentAlpha::vpMomentAlpha ( )

Empty constructor. Initializes alpha moment as a reference alpha. A default-constructed alpha moment may be used as a reference for other alphas. A reference alpha is class harbouring an alpha value computed for a $[-\pi/2..\pi/2]$ portion of the circle. Not setting a reference alpha will prevent you from doing more than 180deg rotation with moments.

Definition at line 52 of file vpMomentAlpha.cpp.

References vpMoment::values.

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

Common constructor. Initializes alpha moment as a non-reference alpha. A default-constructed alpha moment must be used as a reference for other this alpha. A reference alpha is class harbouring an alpha value computed for a $[0..\pi]$ portion of the circle. Not having a reference alpha will prevent you from doing more than 180deg rotation with moments.

Parameters

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

Definition at line 64 of file vpMomentAlpha.cpp.

References vpMoment::values.

Member Function Documentation

void vpMomentAlpha::compute ( )

virtual

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

Implements vpMoment.

Definition at line 76 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 ( )

inline

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

Definition at line 213 of file vpMomentAlpha.h.

Referenced by vpMomentCommon::getAlpha().

vpMomentDatabase& vpMoment::getMoments ( )

inlineprotectedinherited

Returns the linked moment database.

Returns: the moment database

Definition at line 115 of file vpMoment.h.

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

vpMomentObject& vpMoment::getObject ( )

inlineinherited

Definition at line 119 of file vpMoment.h.

void vpMoment::linkTo ( vpMomentDatabase & moments )

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 <visp/vpMomentObject.h>

#include <visp/vpPoint.h>

#include <visp/vpMomentGravityCenter.h>

#include <visp/vpMomentDatabase.h>

#include <visp/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

moments : database of moment primitives.

Definition at line 104 of file vpMoment.cpp.

References vpMoment::name().

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

const char* vpMomentAlpha::name ( )

inlinevirtual

Moment name.

Implements vpMoment.

Definition at line 217 of file vpMomentAlpha.h.

void vpMoment::update ( vpMomentObject & object )

inherited

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

Parameters

object : object descriptor of the current camera vision.

Definition at line 117 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 orientation.

Definition at line 151 of file vpMomentAlpha.cpp.

Member Data Documentation

std::vector<double> vpMoment::values

protectedinherited

Definition at line 110 of file vpMoment.h.

Referenced by vpMomentArea::compute(), vpMomentGravityCenterNormalized::compute(), vpMomentCentered::compute(), vpMomentGravityCenter::compute(), vpMomentAreaNormalized::compute(), vpMomentCInvariant::compute(), compute(), vpMomentCentered::get(), vpMomentGravityCenter::get(), 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