G2O 通过工厂函数类 OptimizationAlgorithmFactory 来生成固定搭配的优化算法

         OptimizationAlgorithmFactory 类位于 optimization_algorithm_factory.h

//***g2o源码 g2o/g2o/core/optimization_algorithm_factory.h ***//
/*** \brief create solvers based on their short name** Factory to allocate solvers based on their short name.* The Factory is implemented as a sigleton and the single* instance can be accessed via the instance() function.*/
/*** \brief 工厂类用于根据优化算法的名称创建不同的优化算法（OptimizationAlgorithm）** 工厂类是单例模式（singleton）的实现，可以通过instance()方法获取唯一的实例，* 并通过destroy()方法释放实例。*/class G2O_CORE_API OptimizationAlgorithmFactory{public:typedef std::list<AbstractOptimizationAlgorithmCreator*>      CreatorList;//! return the instance//! 获取工厂类的唯一实例static OptimizationAlgorithmFactory* instance();//! free the instance//! 释放唯一实例static void destroy();/*** register a specific creator for allocating a solver* 注册特定的创建者 creator 以分配求解器 solver*/void registerSolver(AbstractOptimizationAlgorithmCreator* c);/*** unregister a specific creator for allocating a solver*/void unregisterSolver(AbstractOptimizationAlgorithmCreator* c);/*** construct a solver based on its name, e.g., var, fix3_2_cholmod* 根据名称 tag 来创建求解器 solver*/OptimizationAlgorithm* construct(const std::string& tag, OptimizationAlgorithmProperty& solverProperty) const;//! list the known solvers into a stream//! 将已知的求解器 solver 列到流中void listSolvers(std::ostream& os) const;//! return the underlying list of creators//! 返回创建者 creators 的基本列表const CreatorList& creatorList() const { return _creator;}protected:OptimizationAlgorithmFactory();~OptimizationAlgorithmFactory();CreatorList _creator;CreatorList::const_iterator findSolver(const std::string& name) const;CreatorList::iterator findSolver(const std::string& name);private:static OptimizationAlgorithmFactory* factoryInstance;};

        示例代码： 

// 这里使用一个工厂函数同时初始化迭代方式和线性求解方式，后续可以将迭代方式(总求解器 solver)和线性求解方式(线性求解器 LinearSolver)分开// 创建一个指向g2o::OptimizationAlgorithmFactory的实例指针g2o::OptimizationAlgorithmFactory *solver_factory = g2o::OptimizationAlgorithmFactory::instance();// 定义一个 g2o::OptimizationAlgorithmProperty 类型的对象用于存储与优化算法相关的元信息g2o::OptimizationAlgorithmProperty solver_property;// 根据名称 tag 创建求解器 solver，调用 construct() 时，函数会将所构建的求解器相关的元信息存储到这个对象中，// 比如该求解器的名称、是否需要舒尔补、位姿自由度、地图路标自由度等。g2o::OptimizationAlgorithm *solver = solver_factory->construct("lm_var", solver_property);std::unique_ptr<g2o::SparseOptimizer> graph_ptr_;graph_ptr_.reset(new g2o::SparseOptimizer());graph_ptr_->setAlgorithm(solver);if (!graph_ptr_->solver()) {LOG(ERROR) << "G2O 优化器创建失败！";}// 初始化鲁棒核函数的工厂函数g2o::RobustKernelFactory *robust_kernel_factory_ = g2o::RobustKernelFactory::instance();

        其中，OptimizationAlgorithm* construct(const std::string& tag, OptimizationAlgorithmProperty& solverProperty) const; 函数中 tag 的所有可用算法与其对应描述有： 

//*** g2o源码 g2o/g2o/solvers/cholmod/solver_cholmod.cpp ***//
G2O_REGISTER_OPTIMIZATION_LIBRARY(cholmod);G2O_REGISTER_OPTIMIZATION_ALGORITHM(gn_var_cholmod,new CholmodSolverCreator(OptimizationAlgorithmProperty("gn_var_cholmod","Gauss-Newton: Cholesky solver using CHOLMOD (variable blocksize)","CHOLMOD", false, Eigen::Dynamic, Eigen::Dynamic)));
G2O_REGISTER_OPTIMIZATION_ALGORITHM(gn_fix3_2_cholmod,new CholmodSolverCreator(OptimizationAlgorithmProperty("gn_fix3_2_cholmod","Gauss-Newton: Cholesky solver using CHOLMOD (fixed blocksize)","CHOLMOD", true, 3, 2)));
G2O_REGISTER_OPTIMIZATION_ALGORITHM(gn_fix6_3_cholmod,new CholmodSolverCreator(OptimizationAlgorithmProperty("gn_fix6_3_cholmod","Gauss-Newton: Cholesky solver using CHOLMOD (fixed blocksize)","CHOLMOD", true, 6, 3)));
G2O_REGISTER_OPTIMIZATION_ALGORITHM(gn_fix7_3_cholmod,new CholmodSolverCreator(OptimizationAlgorithmProperty("gn_fix7_3_cholmod","Gauss-Newton: Cholesky solver using CHOLMOD (fixed blocksize)","CHOLMOD", true, 7, 3)));
G2O_REGISTER_OPTIMIZATION_ALGORITHM(lm_var_cholmod,new CholmodSolverCreator(OptimizationAlgorithmProperty("lm_var_cholmod","Levenberg: Cholesky solver using CHOLMOD (variable blocksize)","CHOLMOD", false, Eigen::Dynamic, Eigen::Dynamic)));
G2O_REGISTER_OPTIMIZATION_ALGORITHM(lm_fix3_2_cholmod,new CholmodSolverCreator(OptimizationAlgorithmProperty("lm_fix3_2_cholmod","Levenberg: Cholesky solver using CHOLMOD (fixed blocksize)", "CHOLMOD",true, 3, 2)));
G2O_REGISTER_OPTIMIZATION_ALGORITHM(lm_fix6_3_cholmod,new CholmodSolverCreator(OptimizationAlgorithmProperty("lm_fix6_3_cholmod","Levenberg: Cholesky solver using CHOLMOD (fixed blocksize)", "CHOLMOD",true, 6, 3)));
G2O_REGISTER_OPTIMIZATION_ALGORITHM(lm_fix7_3_cholmod,new CholmodSolverCreator(OptimizationAlgorithmProperty("lm_fix7_3_cholmod","Levenberg: Cholesky solver using CHOLMOD (fixed blocksize)", "CHOLMOD",true, 7, 3)));
G2O_REGISTER_OPTIMIZATION_ALGORITHM(dl_var_cholmod,new CholmodSolverCreator(OptimizationAlgorithmProperty("dl_var_cholmod","Dogleg: Cholesky solver using CHOLMOD (variable blocksize)", "CHOLMOD",false, Eigen::Dynamic, Eigen::Dynamic)));

//*** g2o源码 g2o/g2o/solvers/csparse/solver_csparse.cpp ***//G2O_REGISTER_OPTIMIZATION_LIBRARY(csparse);G2O_REGISTER_OPTIMIZATION_ALGORITHM(gn_var_csparse, new CSparseSolverCreator(OptimizationAlgorithmProperty("gn_var_csparse", "Gauss-Newton: Cholesky solver using CSparse (variable blocksize)", "CSparse", false, Eigen::Dynamic, Eigen::Dynamic)));G2O_REGISTER_OPTIMIZATION_ALGORITHM(gn_fix3_2_csparse, new CSparseSolverCreator(OptimizationAlgorithmProperty("gn_fix3_2_csparse", "Gauss-Newton: Cholesky solver using CSparse (fixed blocksize)", "CSparse", true, 3, 2)));G2O_REGISTER_OPTIMIZATION_ALGORITHM(gn_fix6_3_csparse, new CSparseSolverCreator(OptimizationAlgorithmProperty("gn_fix6_3_csparse", "Gauss-Newton: Cholesky solver using CSparse (fixed blocksize)", "CSparse", true, 6, 3)));G2O_REGISTER_OPTIMIZATION_ALGORITHM(gn_fix7_3_csparse, new CSparseSolverCreator(OptimizationAlgorithmProperty("gn_fix7_3_csparse", "Gauss-Newton: Cholesky solver using CSparse (fixed blocksize)", "CSparse", true, 7, 3)));G2O_REGISTER_OPTIMIZATION_ALGORITHM(lm_var_csparse, new CSparseSolverCreator(OptimizationAlgorithmProperty("lm_var_csparse", "Levenberg: Cholesky solver using CSparse (variable blocksize)", "CSparse", false, Eigen::Dynamic, Eigen::Dynamic)));G2O_REGISTER_OPTIMIZATION_ALGORITHM(lm_fix3_2_csparse, new CSparseSolverCreator(OptimizationAlgorithmProperty("lm_fix3_2_csparse", "Levenberg: Cholesky solver using CSparse (fixed blocksize)", "CSparse", true, 3, 2)));G2O_REGISTER_OPTIMIZATION_ALGORITHM(lm_fix6_3_csparse, new CSparseSolverCreator(OptimizationAlgorithmProperty("lm_fix6_3_csparse", "Levenberg: Cholesky solver using CSparse (fixed blocksize)", "CSparse", true, 6, 3)));G2O_REGISTER_OPTIMIZATION_ALGORITHM(lm_fix7_3_csparse, new CSparseSolverCreator(OptimizationAlgorithmProperty("lm_fix7_3_csparse", "Levenberg: Cholesky solver using CSparse (fixed blocksize)", "CSparse", true, 7, 3)));G2O_REGISTER_OPTIMIZATION_ALGORITHM(dl_var_csparse, new CSparseSolverCreator(OptimizationAlgorithmProperty("dl_var_csparse", "Dogleg: Cholesky solver using CSparse (variable blocksize)", "CSparse", false, Eigen::Dynamic, Eigen::Dynamic)));

//*** g2o源码 g2o/g2o/solvers/eigen/solver_eigen.cpp ***//G2O_REGISTER_OPTIMIZATION_LIBRARY(eigen);G2O_REGISTER_OPTIMIZATION_ALGORITHM(gn_var, new EigenSolverCreator(OptimizationAlgorithmProperty("gn_var", "Gauss-Newton: Cholesky solver using Eigen's Sparse Cholesky methods (variable blocksize)", "Eigen", false, Eigen::Dynamic, Eigen::Dynamic)));G2O_REGISTER_OPTIMIZATION_ALGORITHM(gn_fix3_2, new EigenSolverCreator(OptimizationAlgorithmProperty("gn_fix3_2", "Gauss-Newton: Cholesky solver using  Eigen's Sparse Cholesky (fixed blocksize)", "Eigen", true, 3, 2)));G2O_REGISTER_OPTIMIZATION_ALGORITHM(gn_fix6_3, new EigenSolverCreator(OptimizationAlgorithmProperty("gn_fix6_3", "Gauss-Newton: Cholesky solver using  Eigen's Sparse Cholesky (fixed blocksize)", "Eigen", true, 6, 3)));G2O_REGISTER_OPTIMIZATION_ALGORITHM(gn_fix7_3, new EigenSolverCreator(OptimizationAlgorithmProperty("gn_fix7_3", "Gauss-Newton: Cholesky solver using  Eigen's Sparse Cholesky (fixed blocksize)", "Eigen", true, 7, 3)));G2O_REGISTER_OPTIMIZATION_ALGORITHM(lm_var, new EigenSolverCreator(OptimizationAlgorithmProperty("lm_var", "Levenberg: Cholesky solver using Eigen's Sparse Cholesky methods (variable blocksize)", "Eigen", false, Eigen::Dynamic, Eigen::Dynamic)));G2O_REGISTER_OPTIMIZATION_ALGORITHM(lm_fix3_2, new EigenSolverCreator(OptimizationAlgorithmProperty("lm_fix3_2", "Levenberg: Cholesky solver using  Eigen's Sparse Cholesky (fixed blocksize)", "Eigen", true, 3, 2)));G2O_REGISTER_OPTIMIZATION_ALGORITHM(lm_fix6_3, new EigenSolverCreator(OptimizationAlgorithmProperty("lm_fix6_3", "Levenberg: Cholesky solver using  Eigen's Sparse Cholesky (fixed blocksize)", "Eigen", true, 6, 3)));G2O_REGISTER_OPTIMIZATION_ALGORITHM(lm_fix7_3, new EigenSolverCreator(OptimizationAlgorithmProperty("lm_fix7_3", "Levenberg: Cholesky solver using  Eigen's Sparse Cholesky (fixed blocksize)", "Eigen", true, 7, 3)));G2O_REGISTER_OPTIMIZATION_ALGORITHM(dl_var, new EigenSolverCreator(OptimizationAlgorithmProperty("dl_var", "Dogleg: Cholesky solver using Eigen's Sparse Cholesky methods (variable blocksize)", "Eigen", false, Eigen::Dynamic, Eigen::Dynamic)));

//*** g2o源码 g2o/g2o/solvers/dense/solver_dense.cpp ***//
G2O_REGISTER_OPTIMIZATION_LIBRARY(dense);G2O_REGISTER_OPTIMIZATION_ALGORITHM(gn_dense, new DenseSolverCreator(OptimizationAlgorithmProperty("gn_dense", "Gauss-Newton: Dense solver (variable blocksize)","Dense", false, Eigen::Dynamic, Eigen::Dynamic)));
G2O_REGISTER_OPTIMIZATION_ALGORITHM(gn_dense3_2,new DenseSolverCreator(OptimizationAlgorithmProperty("gn_dense3_2", "Gauss-Newton: Dense solver (fixed blocksize)", "Dense",true, 3, 2)));
G2O_REGISTER_OPTIMIZATION_ALGORITHM(gn_dense6_3,new DenseSolverCreator(OptimizationAlgorithmProperty("gn_dense6_3", "Gauss-Newton: Dense solver (fixed blocksize)", "Dense",true, 6, 3)));
G2O_REGISTER_OPTIMIZATION_ALGORITHM(gn_dense7_3,new DenseSolverCreator(OptimizationAlgorithmProperty("gn_dense7_3", "Gauss-Newton: Dense solver (fixed blocksize)", "Dense",true, 7, 3)));
G2O_REGISTER_OPTIMIZATION_ALGORITHM(lm_dense, new DenseSolverCreator(OptimizationAlgorithmProperty("lm_dense", "Levenberg: Dense solver (variable blocksize)","Dense", false, -1, -1)));
G2O_REGISTER_OPTIMIZATION_ALGORITHM(lm_dense3_2, new DenseSolverCreator(OptimizationAlgorithmProperty("lm_dense3_2", "Levenberg: Dense solver (fixed blocksize)","Dense", true, 3, 2)));
G2O_REGISTER_OPTIMIZATION_ALGORITHM(lm_dense6_3, new DenseSolverCreator(OptimizationAlgorithmProperty("lm_dense6_3", "Levenberg: Dense solver (fixed blocksize)","Dense", true, 6, 3)));
G2O_REGISTER_OPTIMIZATION_ALGORITHM(lm_dense7_3, new DenseSolverCreator(OptimizationAlgorithmProperty("lm_dense7_3", "Levenberg: Dense solver (fixed blocksize)","Dense", true, 7, 3)));

//*** g2o源码 g2o/g2o/solvers/pcg/solver_pcg.cpp ***//
G2O_REGISTER_OPTIMIZATION_LIBRARY(pcg);G2O_REGISTER_OPTIMIZATION_ALGORITHM(gn_pcg, new PCGSolverCreator(OptimizationAlgorithmProperty("gn_pcg","Gauss-Newton: PCG solver using block-Jacobi pre-conditioner ""(variable blocksize)","PCG", false, Eigen::Dynamic, Eigen::Dynamic)));
G2O_REGISTER_OPTIMIZATION_ALGORITHM(gn_pcg3_2, new PCGSolverCreator(OptimizationAlgorithmProperty("gn_pcg3_2","Gauss-Newton: PCG solver using block-Jacobi ""pre-conditioner (fixed blocksize)","PCG", true, 3, 2)));
G2O_REGISTER_OPTIMIZATION_ALGORITHM(gn_pcg6_3, new PCGSolverCreator(OptimizationAlgorithmProperty("gn_pcg6_3","Gauss-Newton: PCG solver using block-Jacobi ""pre-conditioner (fixed blocksize)","PCG", true, 6, 3)));
G2O_REGISTER_OPTIMIZATION_ALGORITHM(gn_pcg7_3, new PCGSolverCreator(OptimizationAlgorithmProperty("gn_pcg7_3","Gauss-Newton: PCG solver using block-Jacobi ""pre-conditioner (fixed blocksize)","PCG", true, 7, 3)));
G2O_REGISTER_OPTIMIZATION_ALGORITHM(lm_pcg, new PCGSolverCreator(OptimizationAlgorithmProperty("lm_pcg","Levenberg: PCG solver using block-Jacobi pre-conditioner ""(variable blocksize)","PCG", false, Eigen::Dynamic, Eigen::Dynamic)));
G2O_REGISTER_OPTIMIZATION_ALGORITHM(lm_pcg3_2, new PCGSolverCreator(OptimizationAlgorithmProperty("lm_pcg3_2","Levenberg: PCG solver using block-Jacobi pre-conditioner ""(fixed blocksize)","PCG", true, 3, 2)));
G2O_REGISTER_OPTIMIZATION_ALGORITHM(lm_pcg6_3, new PCGSolverCreator(OptimizationAlgorithmProperty("lm_pcg6_3","Levenberg: PCG solver using block-Jacobi pre-conditioner ""(fixed blocksize)","PCG", true, 6, 3)));
G2O_REGISTER_OPTIMIZATION_ALGORITHM(lm_pcg7_3, new PCGSolverCreator(OptimizationAlgorithmProperty("lm_pcg7_3","Levenberg: PCG solver using block-Jacobi pre-conditioner ""(fixed blocksize)","PCG", true, 7, 3)));

参考

        [代码实践] G2O 学习记录（一）：2D 位姿图优化

        [代码实践] G2O 学习记录（二）：3D 位姿图优化