Convert pose graph 2D example to glog and gflags. Change-Id: I0ed75a60718ef95199bb36f33d9eb99157d11d40

diff --git a/examples/slam/CMakeLists.txt b/examples/slam/CMakeLists.txt
index a5f12c4..c72aa16 100644
--- a/examples/slam/CMakeLists.txt
+++ b/examples/slam/CMakeLists.txt

@@ -30,7 +30,4 @@
 include_directories(./)
 
 add_subdirectory(pose_graph_2d)
-
-if (GFLAGS)
-  add_subdirectory(pose_graph_3d)
-endif (GFLAGS)
\ No newline at end of file
+add_subdirectory(pose_graph_3d)

diff --git a/examples/slam/pose_graph_2d/CMakeLists.txt b/examples/slam/pose_graph_2d/CMakeLists.txt
index 5574ad1..d654e8c 100644
--- a/examples/slam/pose_graph_2d/CMakeLists.txt
+++ b/examples/slam/pose_graph_2d/CMakeLists.txt

@@ -28,11 +28,12 @@
 #
 # Author: vitus@google.com (Michael Vitus)
 
-add_executable(pose_graph_2d
-  angle_local_parameterization.h
-  normalize_angle.h
-  pose_graph_2d.cc
-  pose_graph_2d_error_term.h
-  types.h)
-target_link_libraries(pose_graph_2d ceres)
-
+if (GFLAGS)
+  add_executable(pose_graph_2d
+    angle_local_parameterization.h
+    normalize_angle.h
+    pose_graph_2d.cc
+    pose_graph_2d_error_term.h
+    types.h)
+  target_link_libraries(pose_graph_2d ceres ${GFLAGS_LIBRARIES})
+endif (GFLAGS)
\ No newline at end of file

diff --git a/examples/slam/pose_graph_2d/pose_graph_2d.cc b/examples/slam/pose_graph_2d/pose_graph_2d.cc
index 969bdb5..b9374db 100644
--- a/examples/slam/pose_graph_2d/pose_graph_2d.cc
+++ b/examples/slam/pose_graph_2d/pose_graph_2d.cc

@@ -42,9 +42,13 @@
 #include "angle_local_parameterization.h"
 #include "ceres/ceres.h"
 #include "common/read_g2o.h"
+#include "gflags/gflags.h"
+#include "glog/logging.h"
 #include "pose_graph_2d_error_term.h"
 #include "types.h"
 
+DEFINE_string(input, "", "The pose graph definition filename in g2o format.");
+
 namespace ceres {
 namespace examples {
 
@@ -56,7 +60,7 @@
   CHECK(poses != NULL);
   CHECK(problem != NULL);
   if (constraints.empty()) {
-    std::cout << "No constraints, no problem to optimize.\n";
+    LOG(INFO) << "No constraints, no problem to optimize.";
     return;
   }
 
@@ -148,37 +152,31 @@
 }  // namespace ceres
 
 int main(int argc, char** argv) {
-  if (argc != 2) {
-    std::cerr << "Need to specify the filename to read as the first and only "
-              << "argument.\n";
-    return -1;
-  }
+  google::InitGoogleLogging(argv[0]);
+  CERES_GFLAGS_NAMESPACE::ParseCommandLineFlags(&argc, &argv, true);
+
+  CHECK(FLAGS_input != "") << "Need to specify the filename to read.";
 
   std::map<int, ceres::examples::Pose2d> poses;
   std::vector<ceres::examples::Constraint2d> constraints;
 
-  if (!ceres::examples::ReadG2oFile(argv[1], &poses, &constraints)) {
-    return -1;
-  }
+  CHECK(ceres::examples::ReadG2oFile(FLAGS_input, &poses, &constraints))
+      << "Error reading the file: " << FLAGS_input;
 
   std::cout << "Number of poses: " << poses.size() << '\n';
   std::cout << "Number of constraints: " << constraints.size() << '\n';
 
-  if (!ceres::examples::OutputPoses("poses_original.txt", poses)) {
-    return -1;
-  }
+  CHECK(ceres::examples::OutputPoses("poses_original.txt", poses))
+      << "Error outputting to poses_original.txt";
 
   ceres::Problem problem;
   ceres::examples::BuildOptimizationProblem(constraints, &poses, &problem);
 
-  if (!ceres::examples::SolveOptimizationProblem(&problem)) {
-    std::cout << "The solve was not successful, exiting.\n";
-    return -1;
-  }
+  CHECK(ceres::examples::SolveOptimizationProblem(&problem))
+      << "The solve was not successful, exiting.";
 
-  if (!ceres::examples::OutputPoses("poses_optimized.txt", poses)) {
-    return -1;
-  }
+  CHECK(ceres::examples::OutputPoses("poses_optimized.txt", poses))
+      << "Error outputting to poses_original.txt";
 
   return 0;
 }

diff --git a/examples/slam/pose_graph_3d/CMakeLists.txt b/examples/slam/pose_graph_3d/CMakeLists.txt
index 1be4e85..2c5fdc3 100644
--- a/examples/slam/pose_graph_3d/CMakeLists.txt
+++ b/examples/slam/pose_graph_3d/CMakeLists.txt

@@ -28,5 +28,7 @@
 #
 # Author: vitus@google.com (Michael Vitus)
 
-add_executable(pose_graph_3d pose_graph_3d.cc)
-target_link_libraries(pose_graph_3d ceres ${GFLAGS_LIBRARIES})
+if (GFLAGS)
+  add_executable(pose_graph_3d pose_graph_3d.cc)
+  target_link_libraries(pose_graph_3d ceres ${GFLAGS_LIBRARIES})
+endif (GFLAGS)
\ No newline at end of file

diff --git a/examples/slam/pose_graph_3d/pose_graph_3d.cc b/examples/slam/pose_graph_3d/pose_graph_3d.cc
index 191758d..dcc85af 100644
--- a/examples/slam/pose_graph_3d/pose_graph_3d.cc
+++ b/examples/slam/pose_graph_3d/pose_graph_3d.cc

@@ -39,8 +39,7 @@
 #include "pose_graph_3d_error_term.h"
 #include "types.h"
 
-DEFINE_string(input_filename, "",
-              "The pose graph definition filename in g2o format.");
+DEFINE_string(input, "", "The pose graph definition filename in g2o format.");
 
 namespace ceres {
 namespace examples {
@@ -148,14 +147,13 @@
   google::InitGoogleLogging(argv[0]);
   CERES_GFLAGS_NAMESPACE::ParseCommandLineFlags(&argc, &argv, true);
 
-  CHECK(FLAGS_input_filename != "") << "Need to specify the filename to read.";
+  CHECK(FLAGS_input != "") << "Need to specify the filename to read.";
 
   ceres::examples::MapOfPoses poses;
   ceres::examples::VectorOfConstraints constraints;
 
-  CHECK(
-      ceres::examples::ReadG2oFile(FLAGS_input_filename, &poses, &constraints))
-      << "Error reading the file: " << FLAGS_input_filename;
+  CHECK(ceres::examples::ReadG2oFile(FLAGS_input, &poses, &constraints))
+      << "Error reading the file: " << FLAGS_input;
 
   std::cout << "Number of poses: " << poses.size() << '\n';
   std::cout << "Number of constraints: " << constraints.size() << '\n';