1 // Ceres Solver - A fast non-linear least squares minimizer
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3 // http://ceres-solver.org/
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29 // Author: vitus@google.com (Michael Vitus)
31 // An example of solving a graph-based formulation of Simultaneous Localization
32 // and Mapping (SLAM). It reads a 2D pose graph problem definition file in the
33 // g2o format, formulates and solves the Ceres optimization problem, and outputs
34 // the original and optimized poses to file for plotting.
42 #include "angle_local_parameterization.h"
43 #include "ceres/ceres.h"
44 #include "common/read_g2o.h"
45 #include "gflags/gflags.h"
46 #include "glog/logging.h"
47 #include "pose_graph_2d_error_term.h"
50 DEFINE_string(input, "", "The pose graph definition filename in g2o format.");
55 // Constructs the nonlinear least squares optimization problem from the pose
57 void BuildOptimizationProblem(const std::vector<Constraint2d>& constraints,
58 std::map<int, Pose2d>* poses,
59 ceres::Problem* problem) {
61 CHECK(problem != NULL);
62 if (constraints.empty()) {
63 LOG(INFO) << "No constraints, no problem to optimize.";
67 ceres::LossFunction* loss_function = NULL;
68 ceres::LocalParameterization* angle_local_parameterization =
69 AngleLocalParameterization::Create();
71 for (std::vector<Constraint2d>::const_iterator constraints_iter =
73 constraints_iter != constraints.end(); ++constraints_iter) {
74 const Constraint2d& constraint = *constraints_iter;
76 std::map<int, Pose2d>::iterator pose_begin_iter =
77 poses->find(constraint.id_begin);
78 CHECK(pose_begin_iter != poses->end())
79 << "Pose with ID: " << constraint.id_begin << " not found.";
80 std::map<int, Pose2d>::iterator pose_end_iter =
81 poses->find(constraint.id_end);
82 CHECK(pose_end_iter != poses->end())
83 << "Pose with ID: " << constraint.id_end << " not found.";
85 const Eigen::Matrix3d sqrt_information =
86 constraint.information.llt().matrixL();
87 // Ceres will take ownership of the pointer.
88 ceres::CostFunction* cost_function = PoseGraph2dErrorTerm::Create(
89 constraint.x, constraint.y, constraint.yaw_radians, sqrt_information);
90 problem->AddResidualBlock(
91 cost_function, loss_function, &pose_begin_iter->second.x,
92 &pose_begin_iter->second.y, &pose_begin_iter->second.yaw_radians,
93 &pose_end_iter->second.x, &pose_end_iter->second.y,
94 &pose_end_iter->second.yaw_radians);
96 problem->SetParameterization(&pose_begin_iter->second.yaw_radians,
97 angle_local_parameterization);
98 problem->SetParameterization(&pose_end_iter->second.yaw_radians,
99 angle_local_parameterization);
102 // The pose graph optimization problem has three DOFs that are not fully
103 // constrained. This is typically referred to as gauge freedom. You can apply
104 // a rigid body transformation to all the nodes and the optimization problem
105 // will still have the exact same cost. The Levenberg-Marquardt algorithm has
106 // internal damping which mitigate this issue, but it is better to properly
107 // constrain the gauge freedom. This can be done by setting one of the poses
108 // as constant so the optimizer cannot change it.
109 std::map<int, Pose2d>::iterator pose_start_iter =
111 CHECK(pose_start_iter != poses->end()) << "There are no poses.";
112 problem->SetParameterBlockConstant(&pose_start_iter->second.x);
113 problem->SetParameterBlockConstant(&pose_start_iter->second.y);
114 problem->SetParameterBlockConstant(&pose_start_iter->second.yaw_radians);
117 // Returns true if the solve was successful.
118 bool SolveOptimizationProblem(ceres::Problem* problem) {
119 CHECK(problem != NULL);
121 ceres::Solver::Options options;
122 options.max_num_iterations = 100;
123 options.linear_solver_type = ceres::SPARSE_NORMAL_CHOLESKY;
125 ceres::Solver::Summary summary;
126 ceres::Solve(options, problem, &summary);
128 std::cout << summary.FullReport() << '\n';
130 return summary.IsSolutionUsable();
133 // Output the poses to the file with format: ID x y yaw_radians.
134 bool OutputPoses(const std::string& filename,
135 const std::map<int, Pose2d>& poses) {
136 std::fstream outfile;
137 outfile.open(filename.c_str(), std::istream::out);
139 std::cerr << "Error opening the file: " << filename << '\n';
142 for (std::map<int, Pose2d>::const_iterator poses_iter = poses.begin();
143 poses_iter != poses.end(); ++poses_iter) {
144 const std::map<int, Pose2d>::value_type& pair = *poses_iter;
145 outfile << pair.first << " " << pair.second.x << " " << pair.second.y
146 << ' ' << pair.second.yaw_radians << '\n';
151 } // namespace examples
154 int main(int argc, char** argv) {
155 google::InitGoogleLogging(argv[0]);
156 CERES_GFLAGS_NAMESPACE::ParseCommandLineFlags(&argc, &argv, true);
158 CHECK(FLAGS_input != "") << "Need to specify the filename to read.";
160 std::map<int, ceres::examples::Pose2d> poses;
161 std::vector<ceres::examples::Constraint2d> constraints;
163 CHECK(ceres::examples::ReadG2oFile(FLAGS_input, &poses, &constraints))
164 << "Error reading the file: " << FLAGS_input;
166 std::cout << "Number of poses: " << poses.size() << '\n';
167 std::cout << "Number of constraints: " << constraints.size() << '\n';
169 CHECK(ceres::examples::OutputPoses("poses_original.txt", poses))
170 << "Error outputting to poses_original.txt";
172 ceres::Problem problem;
173 ceres::examples::BuildOptimizationProblem(constraints, &poses, &problem);
175 CHECK(ceres::examples::SolveOptimizationProblem(&problem))
176 << "The solve was not successful, exiting.";
178 CHECK(ceres::examples::OutputPoses("poses_optimized.txt", poses))
179 << "Error outputting to poses_original.txt";