stat.h

/*****************************************************************************
 * VCLib                                                                     *
 * Visual Computing Library                                                  *
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 * Copyright(C) 2021-2025                                                    *
 * Visual Computing Lab                                                      *
 * ISTI - Italian National Research Council                                  *
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the              *
 * Mozilla Public License Version 2.0                                        *
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 ****************************************************************************/
 
#ifndef VCL_ALGORITHMS_CORE_STAT_H
#define VCL_ALGORITHMS_CORE_STAT_H
 
#include <vclib/space/core/matrix.h>
#include <vclib/space/core/polygon.h>
 
#include <vector>
 
namespace vcl {
 
template<Point3Concept PointType>
auto covarianceMatrixOfPointCloud(const std::vector<PointType>& pointVec)
{
    Matrix33<typename PointType::ScalarType> m;
    m.setZero();
    PointType barycenter = Polygon<PointType>::barycenter(pointVec);
 
    // compute covariance matrix
    for (const PointType& p : pointVec) {
        PointType e = p - barycenter;
        m += e.outerProduct(e);
    }
    return m;
}
 
template<Point3Concept PointType>
auto weightedCovarianceMatrixOfPointCloud(
    const std::vector<PointType>&                      pointVec,
    const std::vector<typename PointType::ScalarType>& weights)
{
    Matrix33<typename PointType::ScalarType> m;
    m.setZero();
    PointType barycenter =
        Polygon<PointType>::weightedBarycenter(pointVec, weights);
 
    // compute covariance matrix
    typename PointType::ScalarType wsum = 0;
    for (uint i = 0; i < pointVec.size(); ++i) {
        PointType e = (pointVec[i] - barycenter) * weights[i];
        m += e.outerProduct(e);
        wsum += weights[i];
    }
    return m / wsum;
}
 
} // namespace vcl
 
#endif // VCL_ALGORITHMS_CORE_STAT_H