frc::AprilTagDetection Class Reference

A detection of an AprilTag tag. More...

#include <frc/apriltag/AprilTagDetection.h>

Classes
struct	Point
	A point. More...

Public Member Functions
	AprilTagDetection ()=delete
	AprilTagDetection (const AprilTagDetection &)=delete
AprilTagDetection &	operator= (const AprilTagDetection &)=delete
std::string_view	GetFamily () const
	Gets the decoded tag's family name. More...
int	GetId () const
	Gets the decoded ID of the tag. More...
int	GetHamming () const
	Gets how many error bits were corrected. More...
float	GetDecisionMargin () const
	Gets a measure of the quality of the binary decoding process: the average difference between the intensity of a data bit versus the decision threshold. More...
std::span< const double, 9 >	GetHomography () const
	Gets the 3x3 homography matrix describing the projection from an "ideal" tag (with corners at (-1,1), (1,1), (1,-1), and (-1, -1)) to pixels in the image. More...
Eigen::Matrix3d	GetHomographyMatrix () const
	Gets the 3x3 homography matrix describing the projection from an "ideal" tag (with corners at (-1,1), (1,1), (1,-1), and (-1, -1)) to pixels in the image. More...
const Point &	GetCenter () const
	Gets the center of the detection in image pixel coordinates. More...
const Point &	GetCorner (int ndx) const
	Gets a corner of the tag in image pixel coordinates. More...
std::span< double, 8 >	GetCorners (std::span< double, 8 > cornersBuf) const
	Gets the corners of the tag in image pixel coordinates. More...

Detailed Description

A detection of an AprilTag tag.

Constructor & Destructor Documentation

AprilTagDetection() [1/2]

frc::AprilTagDetection::AprilTagDetection ( )

delete

AprilTagDetection() [2/2]

frc::AprilTagDetection::AprilTagDetection ( const AprilTagDetection &  )

delete

Member Function Documentation

GetCenter()

const Point & frc::AprilTagDetection::GetCenter ( ) const

inline

Gets the center of the detection in image pixel coordinates.

Returns

Center point

GetCorner()

const Point & frc::AprilTagDetection::GetCorner ( int  ndx ) const

inline

Gets a corner of the tag in image pixel coordinates.

These always wrap counter-clock wise around the tag. Index 0 is the bottom left corner.

Parameters

ndx	Corner index (range is 0-3, inclusive)

Returns

Corner point

GetCorners()

std::span< double, 8 > frc::AprilTagDetection::GetCorners ( std::span< double, 8 >  cornersBuf ) const

inline

Gets the corners of the tag in image pixel coordinates.

These always wrap counter-clock wise around the tag. The first set of corner coordinates are the coordinates for the bottom left corner.

Parameters

cornersBuf

Corner point array (X and Y for each corner in order)

Returns

Corner point array (copy of cornersBuf span)

GetDecisionMargin()

float frc::AprilTagDetection::GetDecisionMargin ( ) const

inline

Gets a measure of the quality of the binary decoding process: the average difference between the intensity of a data bit versus the decision threshold.

Higher numbers roughly indicate better decodes. This is a reasonable measure of detection accuracy only for very small tags– not effective for larger tags (where we could have sampled anywhere within a bit cell and still gotten a good detection.)

Returns

Decision margin

GetFamily()

std::string_view frc::AprilTagDetection::GetFamily

(

)

const

Gets the decoded tag's family name.

Returns

Decoded family name

GetHamming()

int frc::AprilTagDetection::GetHamming ( ) const

inline

Gets how many error bits were corrected.

Note: accepting large numbers of corrected errors leads to greatly increased false positive rates. NOTE: As of this implementation, the detector cannot detect tags with a hamming distance greater than 2.

Returns

Hamming distance (number of corrected error bits)

GetHomography()

std::span< const double, 9 > frc::AprilTagDetection::GetHomography

(

)

const

Gets the 3x3 homography matrix describing the projection from an "ideal" tag (with corners at (-1,1), (1,1), (1,-1), and (-1, -1)) to pixels in the image.

Returns

Homography matrix data

GetHomographyMatrix()

Eigen::Matrix3d frc::AprilTagDetection::GetHomographyMatrix

(

)

const

Gets the 3x3 homography matrix describing the projection from an "ideal" tag (with corners at (-1,1), (1,1), (1,-1), and (-1, -1)) to pixels in the image.

Returns

Homography matrix

GetId()

int frc::AprilTagDetection::GetId ( ) const

inline

Gets the decoded ID of the tag.

Returns

Decoded ID

operator=()

AprilTagDetection & frc::AprilTagDetection::operator= ( const AprilTagDetection &  )

delete

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The documentation for this class was generated from the following file:

• frc/apriltag/AprilTagDetection.h