struct LidarEdgeFactor
{
	LidarEdgeFactor(Eigen::Vector3d curr_point_, Eigen::Vector3d last_point_a_,
					Eigen::Vector3d last_point_b_, double s_)
		: curr_point(curr_point_), last_point_a(last_point_a_), last_point_b(last_point_b_), s(s_) {}

	template <typename T>
	bool operator()(const T *q, const T *t, T *residual) const
	{

		Eigen::Matrix<T, 3, 1> cp{T(curr_point.x()), T(curr_point.y()), T(curr_point.z())};
		Eigen::Matrix<T, 3, 1> lpa{T(last_point_a.x()), T(last_point_a.y()), T(last_point_a.z())};
		Eigen::Matrix<T, 3, 1> lpb{T(last_point_b.x()), T(last_point_b.y()), T(last_point_b.z())};

		//Eigen::Quaternion<T> q_last_curr{q[3], T(s) * q[0], T(s) * q[1], T(s) * q[2]};
		Eigen::Quaternion<T> q_last_curr{q[3], q[0], q[1], q[2]};
		Eigen::Quaternion<T> q_identity{T(1), T(0), T(0), T(0)};
		q_last_curr = q_identity.slerp(T(s), q_last_curr);
		Eigen::Matrix<T, 3, 1> t_last_curr{T(s) * t[0], T(s) * t[1], T(s) * t[2]};

		Eigen::Matrix<T, 3, 1> lp;
		lp = q_last_curr * cp + t_last_curr;

		Eigen::Matrix<T, 3, 1> nu = (lp - lpa).cross(lp - lpb);
		Eigen::Matrix<T, 3, 1> de = lpa - lpb;

		residual[0] = nu.x() / de.norm();
		residual[1] = nu.y() / de.norm();
		residual[2] = nu.z() / de.norm();

		return true;
	}

	static ceres::CostFunction *Create(const Eigen::Vector3d curr_point_, const Eigen::Vector3d last_point_a_,
									   const Eigen::Vector3d last_point_b_, const double s_)
	{
		return (new ceres::AutoDiffCostFunction<
				LidarEdgeFactor, 3, 4, 3>(
			new LidarEdgeFactor(curr_point_, last_point_a_, last_point_b_, s_)));
	}

	Eigen::Vector3d curr_point, last_point_a, last_point_b;
	double s;
};

1.自动求导：

 (new ceres::AutoDiffCostFunction<
				LidarEdgeFactor, 3, 4, 3>(
			new LidarEdgeFactor(curr_point_, last_point_a_, last_point_b_, s_)));

①类名lidarEdgeFactor②残差维数3维③参数块维数4（四元数）④参数块维数3（平移量）