BullseyeDetectorStereo.h

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/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */
 
#ifndef OCEAN_CV_DETECTOR_BULLSEYES_BULLSEYEDETECTORSTEREO_H
#define OCEAN_CV_DETECTOR_BULLSEYES_BULLSEYEDETECTORSTEREO_H
 
#include "ocean/cv/detector/bullseyes/Bullseyes.h"
 
#include "ocean/cv/detector/bullseyes/Bullseye.h"
#include "ocean/cv/detector/bullseyes/BullseyeDetectorMono.h"
 
#include "ocean/base/Frame.h"
#include "ocean/base/Worker.h"
#include "ocean/base/Utilities.h"
 
#include "ocean/math/AnyCamera.h"
#include "ocean/math/Matrix.h"
#include "ocean/math/Vector3.h"
 
namespace Ocean
{
 
namespace CV
{
 
namespace Detector
{
 
namespace Bullseyes
{
 
/**
 * This class implements a stereo detector for bullseye patterns.
 * @ingroup cvdetectorbullseyes
 */
class OCEAN_CV_DETECTOR_BULLSEYES_EXPORT BullseyeDetectorStereo
{
    public:
 
        /**
         * Definition of a pair of bullseyes.
         */
        using BullseyePair = std::pair<Bullseye, Bullseye>;
 
        /**
         * Definition of a vector holding bullseye pairs.
         */
        using BullseyePairs = std::vector<BullseyePair>;
 
        /**
         * Definition of a pair of vectors of bullseyes, one from each camera.
         */
        using BullseyeGroup = std::array<Bullseyes, 2>;
 
        /**
         * This class holds the most important parameters for the stereo detector.
         * Currently, this class inherits all parameters from the monocular detector.
         */
        class Parameters : public BullseyeDetectorMono::Parameters
        {
            public:
 
                /**
                 * Creates a new parameter object with default parameters.
                 */
                Parameters() = default;
 
                /**
                 * Returns the default parameters for the stereo detector.
                 * @return The default parameters
                 */
                static Parameters defaultParameters();
        };
 
    protected:
 
        /**
         * This class represents a candidate bullseye match between two stereo cameras.
         * A candidate includes the triangulated 3D center position and the reprojection errors for
         * both cameras. The indices of the matched bullseyes are stored separately as keys in the
         * CandidateMap. Candidates are used during the matching process before final validation and
         * selection.
         */
        class Candidate
        {
            public:
 
                /**
                 * Creates a default (invalid) candidate.
                 */
                Candidate() = default;
 
                /**
                 * Creates a new candidate with the specified parameters.
                 * The indices of the matched bullseyes are not stored in the candidate itself,
                 * but rather as keys in the CandidateMap that holds this candidate.
                 * @param center The triangulated 3D center position in world coordinates
                 * @param reprojectionErrorA The reprojection error for camera A, in pixels
                 * @param reprojectionErrorB The reprojection error for camera B, in pixels
                 */
                Candidate(const Vector3& center, const Scalar reprojectionErrorA, const Scalar reprojectionErrorB);
 
                /**
                 * Returns whether this candidate is valid.
                 * @return True if the candidate has valid indices and center position, otherwise false
                 */
                bool isValid() const;
 
                /**
                 * Returns the triangulated 3D center position.
                 * @return The 3D center position in world coordinates
                 */
                const Vector3& center() const;
 
                /**
                 * Returns the reprojection error for camera A.
                 * @return The reprojection error in pixels
                 */
                Scalar reprojectionErrorA() const;
 
                /**
                 * Returns the reprojection error for camera B.
                 * @return The reprojection error in pixels
                 */
                Scalar reprojectionErrorB() const;
 
                /**
                 * Returns an invalid bullseye center value used as a sentinel for uninitialized positions.
                 * @return The invalid center position
                 */
                static Vector3 invalidBullseyeCenter();
 
            protected:
 
                /// The triangulated 3D center position in world coordinates
                Vector3 center_ = invalidBullseyeCenter();
 
                /// The reprojection error for camera A, in pixels
                Scalar reprojectionErrorA_ = Numeric::minValue();
 
                /// The reprojection error for camera B, in pixels
                Scalar reprojectionErrorB_ = Numeric::minValue();
        };
 
        /**
         * Definition of an unordered map holding candidate bullseyes.
         * The key is a pair of indices (indexA, indexB) where indexA corresponds to a bullseye in camera A
         * and indexB corresponds to a bullseye in camera B. The value is the Candidate object containing
         * the triangulated 3D position and reprojection errors for this match.
         */
        using CandidateMap = std::unordered_map<IndexPair32, Candidate, PairHash>;
 
    public:
 
        /**
         * Detects bullseyes in a pair of stereo frames.
         * @param cameras The camera profiles for the stereo pair, must contain exactly 2 valid cameras
         * @param yFrames The stereo frames in which bullseyes will be detected, must contain exactly 2 valid 8-bit grayscale frames
         * @param world_T_device The transformation from the device coordinate system to the world coordinate system, must be valid
         * @param device_T_cameras The transformations from each camera coordinate system to the device coordinate system, must contain exactly 2 valid transformations
         * @param bullseyePairs The resulting pairs of detected bullseyes, one from each camera
         * @param bullseyeCenters The resulting 3D positions of the triangulated bullseye centers in world coordinates
         * @param parameters The parameters for the detector, must be valid
         * @param worker Optional worker to distribute the computation
         * @return True, if succeeded
         */
        static bool detectBullseyes(const SharedAnyCameras& cameras, const Frames& yFrames, const HomogenousMatrix4& world_T_device, const HomogenousMatrices4& device_T_cameras, BullseyePairs& bullseyePairs, Vectors3& bullseyeCenters, const Parameters& parameters = Parameters::defaultParameters(), Worker* worker = nullptr);
 
    protected:
 
        /**
         * Extracts and validates candidate bullseye matches between two stereo cameras.
         * This function triangulates all possible bullseye pairs and returns those that produce valid 3D positions.
         * The returned map uses index pairs (indexA, indexB) as keys, where indexA corresponds to a bullseye in camera A
         * and indexB corresponds to a bullseye in camera B. The values are Candidate objects containing the triangulated
         * 3D positions and reprojection errors for each matched pair.
         * @param cameraA The camera profile for the first camera, must be valid
         * @param cameraB The camera profile for the second camera, must be valid
         * @param world_T_cameraA The transformation from camera A coordinate system to world coordinate system, must be valid
         * @param world_T_cameraB The transformation from camera B coordinate system to world coordinate system, must be valid
         * @param bullseyesA The bullseyes detected in camera A, may be empty
         * @param bullseyesB The bullseyes detected in camera B, may be empty
         * @return The map of valid candidate matches; may be empty if no valid matches were found
         */
        static CandidateMap extractBullseyeCandidates(const AnyCamera& cameraA, const AnyCamera& cameraB, const HomogenousMatrix4& world_T_cameraA, const HomogenousMatrix4& world_T_cameraB, const Bullseyes& bullseyesA, const Bullseyes& bullseyesB);
 
        /**
         * Extracts the final bullseye pairs and their 3D centers from candidate matches.
         * This function uses the candidate map to retrieve the original bullseye objects and their triangulated positions.
         * @param cameraA The camera profile for the first camera, must be valid
         * @param cameraB The camera profile for the second camera, must be valid
         * @param bullseyesA The bullseyes detected in camera A, must not be empty
         * @param bullseyesB The bullseyes detected in camera B, must not be empty
         * @param candidateMap The map of candidate matches with index pairs as keys and triangulated positions as values, must not be empty
         * @param bullseyePairs The resulting validated bullseye pairs
         * @param bullseyeCenters The resulting 3D positions of the bullseye centers in world coordinates
         * @return True if extraction succeeded, otherwise false
         */
        static bool extractBullseyes(const AnyCamera& cameraA, const AnyCamera& cameraB, const Bullseyes& bullseyesA, const Bullseyes& bullseyesB, const CandidateMap& candidateMap, BullseyePairs& bullseyePairs, Vectors3& bullseyeCenters);
 
        /**
         * Computes a cost matrix for matching bullseyes based on candidate triangulation results.
         * The cost matrix dimensions are (numBullseyesA x numBullseyesB), where each element (i, j)
         * contains the cost of matching bullseye i from camera A with bullseye j from camera B.
         * Costs are based on the triangulation quality (reprojection errors) and geometric consistency
         * (comparing bullseye radii across cameras using the camera scale factor).
         * @param cameraA The camera profile for the first camera, must be valid
         * @param cameraB The camera profile for the second camera, must be valid
         * @param bullseyesA The bullseyes detected in camera A, must not be empty
         * @param bullseyesB The bullseyes detected in camera B, must not be empty
         * @param candidateMap The map of candidate matches to evaluate, must not be empty
         * @param costMatrix The resulting cost matrix with dimensions (numBullseyesA x numBullseyesB)
         * @return True if the cost matrix was successfully computed, otherwise false
         */
        static bool computeCostMatrix(const AnyCamera& cameraA, const AnyCamera& cameraB, const Bullseyes& bullseyesA, const Bullseyes& bullseyesB, const CandidateMap& candidateMap, Matrix& costMatrix);
 
        /**
         * Returns an invalid (arbitrarily large) matching cost value used to indicate that two bullseyes cannot be matched.
         * This value is large enough to prevent matching but not so large as to cause numerical issues.
         * @return The invalid matching cost value
         */
        constexpr static Scalar invalidMatchingCost();
 
        /**
         * Triangulates a single matched bullseye pair to compute its 3D position in world coordinates.
         * This function casts rays from both camera centers through the bullseye positions and finds their nearest point
         * to determine the 3D location. It also computes reprojection errors to assess triangulation quality.
         * @param cameraA The camera profile for the first camera, must be valid
         * @param cameraB The camera profile for the second camera, must be valid
         * @param world_T_cameraA The transformation from camera A coordinate system to world coordinate system, must be valid
         * @param world_T_cameraB The transformation from camera B coordinate system to world coordinate system, must be valid
         * @param bullseyeA The bullseye from camera A, must be valid and within camera A's field of view
         * @param bullseyeB The bullseye from camera B, must be valid and within camera B's field of view
         * @param bullseyeCenter The resulting 3D position of the bullseye center in world coordinates
         * @param reprojectionErrorA The resulting reprojection error for camera A, in pixels
         * @param reprojectionErrorB The resulting reprojection error for camera B, in pixels
         * @return True if triangulation succeeded and the 3D point is in front of both cameras, otherwise false
         */
        static bool triangulateBullseye(const AnyCamera& cameraA, const AnyCamera& cameraB, const HomogenousMatrix4& world_T_cameraA, const HomogenousMatrix4& world_T_cameraB, const Bullseye& bullseyeA, const Bullseye& bullseyeB, Vector3& bullseyeCenter, Scalar& reprojectionErrorA, Scalar& reprojectionErrorB);
};
 
constexpr Scalar BullseyeDetectorStereo::invalidMatchingCost()
{
    // Arbitrarily large value that doesn't cause numerical issues.
    return Scalar(1000);
}
 
} // namespace Bullseyes
 
} // namespace Detector
 
} // namespace CV
 
} // namespace Ocean
 
#endif // OCEAN_CV_DETECTOR_BULLSEYES_BULLSEYEDETECTORSTEREO_H