Spline.hpp

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#pragma once
 
#include <cassert>
#include <cstddef>
#include <vector>
 
#include <unsupported/Eigen/Splines>
 
#include "vc/segmentation/lrps/Common.hpp"
 
namespace volcart::segmentation
{
template <typename Scalar = double, int Degree = 3>
class Spline
{
public:
    using ScalarVector = std::vector<Scalar>;
    using SplineType = Eigen::Spline<Scalar, 2>;
 
    Spline() = default;
 
    Spline(const ScalarVector& xs, const ScalarVector& ys) : npoints_{xs.size()}
    {
        assert(xs.size() == ys.size() && "xs and ys must be same length");
        auto points = make_wide_matrix_(xs, ys);
        spline_ = Eigen::SplineFitting<SplineType>::Interpolate(points, Degree);
    }
 
    Pixel operator()(Scalar t) const
    {
        assert(t >= 0 && t <= 1 && "t must be in range [0, 1]");
        Eigen::Vector2d val = spline_(t);
        return {val(0), val(1)};
    }
 
private:
    std::size_t npoints_;
 
    SplineType spline_;
 
    Eigen::MatrixXd make_wide_matrix_(
        const ScalarVector& xs, const ScalarVector& ys)
    {
        Eigen::MatrixXd mat{2, xs.size()};
        mat.row(0) = Eigen::VectorXd::Map(xs.data(), xs.size());
        mat.row(1) = Eigen::VectorXd::Map(ys.data(), ys.size());
        return mat;
    }
};
 
template <typename Scalar>
using CubicSpline = Spline<Scalar, 3>;
}  // namespace volcart::segmentation