Program Listing for File range_cost_functor.hpp

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#ifndef FUSE_TUTORIALS__RANGE_COST_FUNCTOR_HPP_
#define FUSE_TUTORIALS__RANGE_COST_FUNCTOR_HPP_

#include <ceres/jet.h>

namespace fuse_tutorials
{
class RangeCostFunctor
{
public:
  RangeCostFunctor(const double z, const double sigma)
  : sigma_(sigma), z_(z) {}

  template<typename T>
  bool operator()(
    const T * const robot_position, const T * const beacon_position,
    T * residuals) const
  {
    // Implement our mathematic measurement model:
    //   z_hat = sqrt( (x_robot - x_beacon)^2 + (y_robot - y_beacon)^2 )
    //   error = (z - z_hat) / sigma
    // Unfortunately there is a problem when computing the derivatives. The derivative is undefined
    // when the radicand is zero. To have a well-defined cost function, we implement an alternative
    // cost equation for that case. Thankfully this does not cause any issues with Ceres Solver's
    // auto-diff system. See http://ceres-solver.org/automatic_derivatives.html#pitfalls
    auto dx = robot_position[0] - beacon_position[0];
    auto dy = robot_position[1] - beacon_position[1];
    auto norm_sq = dx * dx + dy * dy;
    if (norm_sq > 0.0) {
      auto z_hat = ceres::sqrt(norm_sq);
      residuals[0] = (T(z_) - z_hat) / T(sigma_);
    } else {
      residuals[0] = T(z_) / T(sigma_);
    }
    return true;
  }

private:
  double sigma_;
  double z_;
};

}  // namespace fuse_tutorials

#endif  // FUSE_TUTORIALS__RANGE_COST_FUNCTOR_HPP_