FeatureDepth¶

class FeatureDepth(self)¶

Bases: BasicFeature

Class that defines a 3D point visual feature \(s\) which is composed by one parameters that is \(log( \frac{Z}{Z^*})\) that defines the current depth relative to the desired depth. Here \(Z\) represents the current depth and \(Z^*\) the desired depth.

In this class \(x\) and \(y\) are the 2D coordinates in the camera frame and are given in meter. \(x\) , \(y\) and \(Z\) are needed during the computation of the interaction matrix \(L\) .

The visual features can be set easily thanks to the buildFrom() method.

As the visual feature \(s\) represents the current depth relative to the desired depth, the desired visual feature \(s^*\) is set to zero. Once the value of the visual feature is set, the interaction() method allows to compute the interaction matrix \(L\) associated to the visual feature, while the error() method computes the error vector \((s - s^*)\) between the current visual feature and the desired one which is here set to zero.

The code below shows how to create a eye-in hand visual servoing task using a 3D depth feature \(log( \frac{Z}{Z^*})\) that corresponds to the current depth relative to the desired depth. To control six degrees of freedom, at least five other features must be considered. First we create a current ( \(s\) ) 3D depth feature. Then we set the task to use the interaction matrix associated to the current feature \(L_s\) . And finally we compute the camera velocity \(v=-\lambda \; L_s^+ \; (s-s^*)\) . The current feature \(s\) is updated in the while() loop.

#include <visp3/visual_features/vpFeatureDepth.h>
#include <visp3/vs/vpServo.h>

int main()
{
  vpServo task; // Visual servoing task

  vpFeatureDepth s; //The current point feature.
  //Set the current parameters x, y, Z and the desired depth Zs
  double x;   // You have to compute the value of x.
  double y;   // You have to compute the value of y.
  double Z;   // You have to compute the value of Z.
  double Zs;  // You have to define the desired depth Zs.
  //Set the point feature thanks to the current parameters.
  s.buildfrom(x, y, Z, log(Z/Zs));

  // Set eye-in-hand control law.
  // The computed velocities will be expressed in the camera frame
  task.setServo(vpServo::EYEINHAND_CAMERA);
  // Interaction matrix is computed with the desired visual features sd
  task.setInteractionMatrixType(vpServo::CURRENT);

  // Add the 3D depth feature to the task
  task.addFeature(s); // s* is here considered as zero

  // Control loop
  for ( ; ; ) {
    // The new parameters x, y and Z must be computed here.

    // Update the current point visual feature
    s.buildfrom(x, y, Z, log(Z/Zs));

    // compute the control law
    vpColVector v = task.computeControlLaw(); // camera velocity
  }
  return 0;
}

If you want to build your own control law, this other example shows how to create a current ( \(s\) ) and desired ( \(s^*\) ) 2D point visual feature, compute the corresponding error vector \((s-s^*)\) and finally build the interaction matrix \(L_s\) .

#include <visp3/core/vpColVector.h>
#include <visp3/core/vpMatrix.h>
#include <visp3/visual_features/vpFeatureDepth.h>

int main()
{
  vpFeatureDepth s; //The current point feature.
  //Set the current parameters x, y, Z and the desired depth Zs
  double x;   // You have to compute the value of x.
  double y;   // You have to compute the value of y.
  double Z;   // You have to compute the value of Z.
  double Zs;  // You have to define the desired depth Zs.
  //Set the point feature thanks to the current parameters.
  s.buildfrom(x, y, Z, log(Z/Zs));

  // Compute the interaction matrix L_s for the current point feature
  vpMatrix L = s.interaction();

  // Compute the error vector (s-s*) for the point feature with s* considered as 0.
  vpColVector s_star(1); // The dimension is 1.
  s_star(1) = 0; // The value of s* is 0.
  s.error(s_star);
}

Default constructor that build a visual feature.

Methods

`__init__`	Default constructor that build a visual feature.
`buildFrom`	Build a 3D depth visual feature from the point coordinates \(x\) and \(y\) given in the camera frame, \(Z\) which describes the depth and \(log(\frac{Z}{Z^*})\) which represents the logarithm of the current depth relative to the desired depth.
`display`	Overloaded function.
`error`	Overloaded function.
`get_LogZoverZstar`	Get the value of \(log(\frac{Z}{Z^*})\) which represents the logarithm of the current depth relative to the desired depth.
`get_Z`	Get the value of \(Z\) which represents the depth in the 3D camera frame.
`get_x`	Get the value of \(x\) which represents the x coordinate of the point in the camera frame.
`get_y`	Get the value of \(y\) which represents the y coordinate of the point in the camera frame.
`init`	Initialize the memory space requested for 3D depth visual feature.
`interaction`	Compute and return the interaction matrix \(L\) .
`print`	Print to stdout the values of the current visual feature \(s\) .
`set_LogZoverZstar`	Set the value of \(log(\frac{Z}{Z^*})\) which represents the logarithm of the current depth relative to the desired depth.
`set_Z`	Set the value of \(Z\) which represents the depth in the 3D camera frame.
`set_x`	Set the value of \(x\) which represents the x coordinate of the point in the camera frame.
`set_xyZLogZoverZstar`	Set the value of \(x\) , \(y\) , \(Z\) and \(log(\frac{Z}{Z^*})\) .
`set_y`	Set the value of \(y\) which represents the y coordinate of the point in the camera frame.

Inherited Methods

`user`
`BasicFeatureSelect`	Indicates who should deallocate the feature.
`setFlags`	Set feature flags to true to prevent warning when re-computing the interaction matrix without having updated the feature.
`FEATURE_ALL`
`getDimension`	Get the feature vector dimension.
`getDeallocate`
`dimension_s`	Return the dimension of the feature vector \(\bf s\) .
`setDeallocate`
`selectAll`	Select all the features.
`get_s`	Get the feature vector \(\bf s\) .
`BasicFeatureDeallocatorType`	Indicates who should deallocate the feature.
`vpServo`

Operators

`__doc__`
`__init__`	Default constructor that build a visual feature.
`__module__`

Attributes

`FEATURE_ALL`
`__annotations__`
`user`
`vpServo`

class BasicFeatureDeallocatorType(self, value: int)¶

Bases: pybind11_object

Indicates who should deallocate the feature.

Values:

user
vpServo

__and__(self, other: object) → object¶

__eq__(self, other: object) → bool¶

__ge__(self, other: object) → bool¶

__getstate__(self) → int¶

__gt__(self, other: object) → bool¶

__hash__(self) → int¶

__index__(self) → int¶

__init__(self, value: int)¶

__int__(self) → int¶

__invert__(self) → object¶

__le__(self, other: object) → bool¶

__lt__(self, other: object) → bool¶

__ne__(self, other: object) → bool¶

__or__(self, other: object) → object¶

__rand__(self, other: object) → object¶

__ror__(self, other: object) → object¶

__rxor__(self, other: object) → object¶

__setstate__(self, state: int) → None¶

__xor__(self, other: object) → object¶

property name : str¶

class BasicFeatureSelect(self, value: int)¶

Bases: pybind11_object

Indicates who should deallocate the feature.

Values:

user
vpServo

__and__(self, other: object) → object¶

__eq__(self, other: object) → bool¶

__ge__(self, other: object) → bool¶

__getstate__(self) → int¶

__gt__(self, other: object) → bool¶

__hash__(self) → int¶

__index__(self) → int¶

__init__(self, value: int)¶

__int__(self) → int¶

__invert__(self) → object¶

__le__(self, other: object) → bool¶

__lt__(self, other: object) → bool¶

__ne__(self, other: object) → bool¶

__or__(self, other: object) → object¶

__rand__(self, other: object) → object¶

__ror__(self, other: object) → object¶

__rxor__(self, other: object) → object¶

__setstate__(self, state: int) → None¶

__xor__(self, other: object) → object¶

property name : str¶

__init__(self)¶: Default constructor that build a visual feature.

buildFrom(self, x: float, y: float, Z: float, LogZoverZstar: float) → None¶

Build a 3D depth visual feature from the point coordinates \(x\) and \(y\) given in the camera frame, \(Z\) which describes the depth and \(log(\frac{Z}{Z^*})\) which represents the logarithm of the current depth relative to the desired depth.

Parameters:

LogZoverZstar: float¶: The \(log(\frac{Z}{Z^*})\) parameter.

dimension_s(self) → int¶: Return the dimension of the feature vector \(\bf s\) .

display(*args, **kwargs)¶

Overloaded function.

display(self: visp._visp.visual_features.FeatureDepth, cam: visp._visp.core.CameraParameters, I: visp._visp.core.ImageGray, color: visp._visp.core.Color = vpColor::green, thickness: int = 1) -> None

Not implemented.

display(self: visp._visp.visual_features.FeatureDepth, cam: visp._visp.core.CameraParameters, I: visp._visp.core.ImageRGBa, color: visp._visp.core.Color = vpColor::green, thickness: int = 1) -> None

Not implemented.

error(*args, **kwargs)¶

Overloaded function.

error(self: visp._visp.visual_features.FeatureDepth, s_star: visp._visp.visual_features.BasicFeature, select: int = FEATURE_ALL) -> visp._visp.core.ColVector

Compute the error \((s-s^*)\) between the current and the desired visual features from a subset of the possible features.

Since this visual feature \(s\) represent the current depth relative to the desired depth, the desired visual feature \(s^*\) should be zero. Thus, the error is here equal to the current visual feature \(s\) .

The code below shows how to use this method:

// Creation of the current feature s
vpFeatureDepth s;

// Creation of the desired feature s^*. By default this feature is
// initialized to zero
vpFeatureDepth s_star;
s_star.setLogZoverZstar(0)

// Compute the interaction matrix for the ThetaU_z feature
vpMatrix L_z = s.interaction();

// Compute the error vector (s-s*) for the ThetaU_z feature
s.error(s_star);

Parameters:

s_star: Desired visual visual feature that should be equal to zero.
select: unuseful in the case of vpFeatureDepth . Always set to FEATURE_ALL.

Returns:

The error \((s-s^*)\) between the current and the desired visual feature.

error(self: visp._visp.visual_features.BasicFeature, s_star: visp._visp.visual_features.BasicFeature, select: int = FEATURE_ALL) -> visp._visp.core.ColVector

Compute the error between two visual features from a subset of the possible features.

getDeallocate(self) → visp._visp.visual_features.BasicFeature.BasicFeatureDeallocatorType¶

getDimension(self, select: int = FEATURE_ALL) → int¶: Get the feature vector dimension.

get_LogZoverZstar(self) → float¶

Get the value of \(log(\frac{Z}{Z^*})\) which represents the logarithm of the current depth relative to the desired depth.

Returns:: The value of \(log(\frac{Z}{Z^*})\) .

get_Z(self) → float¶

Get the value of \(Z\) which represents the depth in the 3D camera frame.

Returns:: The value of \(Z\) .

get_s(self, select: int = FEATURE_ALL) → visp._visp.core.ColVector¶: Get the feature vector \(\bf s\) .

get_x(self) → float¶

Get the value of \(x\) which represents the x coordinate of the point in the camera frame.

Returns:: The value of \(x\) .

get_y(self) → float¶

Get the value of \(y\) which represents the y coordinate of the point in the camera frame.

Returns:: The value of \(y\) .

init(self) → None¶: Initialize the memory space requested for 3D depth visual feature.

interaction(self, select: int = FEATURE_ALL) → visp._visp.core.Matrix¶

Compute and return the interaction matrix \(L\) . The computation is made thanks to the values of the point coordinates \(x\) and \(y\) and the depth \(Z\) .

\[L = \left[\begin{array}{cccccc} 0 & 0 & -1/Z & -y & x & 0 \end{array}\right]\]

The code below shows how to compute the interaction matrix associated to the visual feature \(s = log(\frac{Z}{Z^*})\) .

// Creation of the current feature s
vpFeatureDepth s;
s.buildFrom(0, 0, 5, log(5/1)); // The current depth is 5 meters and the desired is 1 meter.

vpMatrix L_x = s.interaction();

Parameters:

select: int = FEATURE_ALL¶: unuseful in the case of vpFeatureDepth . Always set to FEATURE_ALL.

Returns:

The interaction matrix computed from the point feature.

print(self, select: int = FEATURE_ALL) → None¶

Print to stdout the values of the current visual feature \(s\) .

vpFeatureDepth s; // Current visual feature s

// Creation of the current feature s
s.buildFrom(0, 0, 5, log(5/1));

s.print(); // print all the 2 components of the feature

Parameters:

select: int = FEATURE_ALL¶: unuseful in the case of vpFeatureDepth . Always set to FEATURE_ALL.

static selectAll() → int¶: Select all the features.

setDeallocate(self, d: visp._visp.visual_features.BasicFeature.BasicFeatureDeallocatorType) → None¶

setFlags(self) → None¶: Set feature flags to true to prevent warning when re-computing the interaction matrix without having updated the feature.

set_LogZoverZstar(self, LogZoverZstar: float) → None¶

Set the value of \(log(\frac{Z}{Z^*})\) which represents the logarithm of the current depth relative to the desired depth.

Parameters:

LogZoverZstar: float¶: math:log(frac{Z}{Z^*}) value to set.

set_Z(self, Z: float) → None¶: Set the value of \(Z\) which represents the depth in the 3D camera frame.

set_x(self, x: float) → None¶: Set the value of \(x\) which represents the x coordinate of the point in the camera frame.

set_xyZLogZoverZstar(self, x: float, y: float, Z: float, logZZs: float) → None¶: Set the value of \(x\) , \(y\) , \(Z\) and \(log(\frac{Z}{Z^*})\) . \(x\) and \(y\) represent the coordinates of the point in the camera frame. \(Z\) is the 3D coordinate representing the depth. \(log(\frac{Z}{Z^*})\) represents the logarithm of the current depth relative to the desired depth.

set_y(self, y: float) → None¶: Set the value of \(y\) which represents the y coordinate of the point in the camera frame.