MomentBasic¶

class MomentBasic(self)¶

Bases: Moment

This class defines the 2D basic moment \(m_{ij}\) . This class is a wrapper for vpMomentObject wich allows to use it as a moment. This enables all common operations such as adding to a vpMomentDatabase .

In the case of a dense object O , 2D basic moments are defined by:

\[m_{ij} = \int \int_{O} x^j y^j dx dy\]

In the case of a discrete set of n points, the basic moments are defined by

\[m_{ij} = \sum_{k=1}^{n} x_k^j y_k^j \]

The selection of a dense or discrete object is done in vpMomentObject . The maximum order of vpMomentBasic is the same as that of vpMomentObject (ie: \(i+j \leq\) vpMomentObject::getOrder ).

Note that in the continuous case, the basic moment \(m_{00}\) corresponds to the surface \(a\) of the object. In the discrete case, it is the number of discrete points \(n\) .

Default constructor.

Methods

__init__	Default constructor.
compute	Dummy function.
get	Overloaded function.
name	Moment name.
printDependencies	Overloaded function.

Inherited Methods

linkTo	Links the moment to a database of moment primitives.
getObject
update	Updates the moment with the current object.

Operators

__doc__
__init__	Default constructor.
__module__
__repr__

Attributes

__annotations__

__init__(self)¶

Default constructor.

compute(self) → None¶

Dummy function. Everything is already done in object.

get(*args, **kwargs)¶

Overloaded function.

1. get(self: visp._visp.core.MomentBasic) -> list[float]

Same behaviour as vpMomentObject .

Returns:

all computed moments.

2. get(self: visp._visp.core.MomentBasic, i: int, j: int) -> float

Same behaviour as vpMomentObject .

Parameters:

i

first index of the 2D moment.

j

second index of the 2D moment.

Returns:

\(m_{ij}\) moment.

3. get(self: visp._visp.core.Moment) -> list[float]

Returns:

vector of values

getObject(self) → visp._visp.core.MomentObject¶

linkTo(self, moments: visp._visp.core.MomentDatabase) → None¶

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.

Warning

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()
{
  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)
  vec_p.push_back(p);

  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 contains 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;
}

name(self) → str¶

Moment name.

printDependencies(*args, **kwargs)¶

Overloaded function.

1. printDependencies(self: visp._visp.core.MomentBasic, os: std::ostream) -> None

No dependencies on other vpMoments, since basic moments are computed in vpMomentObject Just prints the basic moments in vpMomentObject with indices

2. printDependencies(self: visp._visp.core.Moment, os: std::ostream) -> None

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

update(self, object: visp._visp.core.MomentObject) → None¶

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