diff --git a/cartographer_ros/cartographer_ros/node.cc b/cartographer_ros/cartographer_ros/node.cc
index c14ba87..a6090f5 100644
--- a/cartographer_ros/cartographer_ros/node.cc
+++ b/cartographer_ros/cartographer_ros/node.cc
@@ -44,6 +44,20 @@
 
 namespace cartographer_ros {
 
+namespace {
+
+cartographer_ros_msgs::SensorTopics DefaultSensorTopics() {
+  cartographer_ros_msgs::SensorTopics topics;
+  topics.laser_scan_topic = kLaserScanTopic;
+  topics.multi_echo_laser_scan_topic = kMultiEchoLaserScanTopic;
+  topics.point_cloud2_topic = kPointCloud2Topic;
+  topics.imu_topic = kImuTopic;
+  topics.odometry_topic = kOdometryTopic;
+  return topics;
+}
+
+}  // namespace
+
 namespace carto = ::cartographer;
 
 using carto::transform::Rigid3d;
@@ -207,7 +221,7 @@ std::unordered_set<string> Node::ComputeExpectedTopics(
     const TrajectoryOptions& options,
     const cartographer_ros_msgs::SensorTopics& topics) {
   std::unordered_set<string> expected_topics;
-
+  // Subscribe to all laser scan, multi echo laser scan, and point cloud topics.
   for (const string& topic : ComputeRepeatedTopicNames(
            topics.laser_scan_topic, options.num_laser_scans)) {
     expected_topics.insert(topic);
@@ -229,6 +243,7 @@ std::unordered_set<string> Node::ComputeExpectedTopics(
            .use_imu_data())) {
     expected_topics.insert(topics.imu_topic);
   }
+  // Odometry is optional.
   if (options.use_odometry) {
     expected_topics.insert(topics.odometry_topic);
   }
@@ -243,6 +258,7 @@ int Node::AddTrajectory(const TrajectoryOptions& options,
       map_builder_bridge_.AddTrajectory(expected_sensor_ids, options);
   AddExtrapolator(trajectory_id, options);
   LaunchSubscribers(options, topics, trajectory_id);
+  is_active_trajectory_[trajectory_id] = true;
   subscribed_topics_.insert(expected_sensor_ids.begin(),
                             expected_sensor_ids.end());
   return trajectory_id;
@@ -328,8 +344,6 @@ void Node::LaunchSubscribers(const TrajectoryOptions& options,
                       ->HandleOdometryMessage(topic, msg);
                 })));
   }
-
-  is_active_trajectory_[trajectory_id] = true;
 }
 
 bool Node::ValidateTrajectoryOptions(const TrajectoryOptions& options) {
@@ -375,25 +389,29 @@ bool Node::HandleStartTrajectory(
     LOG(ERROR) << "Invalid topics.";
     return false;
   }
-
-  const int trajectory_id = AddTrajectory(options, request.topics);
-  response.trajectory_id = trajectory_id;
-
-  is_active_trajectory_[trajectory_id] = true;
+  response.trajectory_id = AddTrajectory(options, request.topics);
   return true;
 }
 
 void Node::StartTrajectoryWithDefaultTopics(const TrajectoryOptions& options) {
   carto::common::MutexLocker lock(&mutex_);
-  cartographer_ros_msgs::SensorTopics topics;
-  topics.laser_scan_topic = kLaserScanTopic;
-  topics.multi_echo_laser_scan_topic = kMultiEchoLaserScanTopic;
-  topics.point_cloud2_topic = kPointCloud2Topic;
-  topics.imu_topic = kImuTopic;
-  topics.odometry_topic = kOdometryTopic;
+  AddTrajectory(options, DefaultSensorTopics());
+}
 
-  const int trajectory_id = AddTrajectory(options, topics);
-  is_active_trajectory_[trajectory_id] = true;
+std::unordered_set<string> Node::ComputeDefaultTopics(
+    const TrajectoryOptions& options) {
+  carto::common::MutexLocker lock(&mutex_);
+  return ComputeExpectedTopics(options, DefaultSensorTopics());
+}
+
+int Node::AddOfflineTrajectory(
+    const std::unordered_set<string>& expected_sensor_ids,
+    const TrajectoryOptions& options) {
+  carto::common::MutexLocker lock(&mutex_);
+  const int trajectory_id =
+      map_builder_bridge_.AddTrajectory(expected_sensor_ids, options);
+  AddExtrapolator(trajectory_id, options);
+  return trajectory_id;
 }
 
 bool Node::HandleFinishTrajectory(
diff --git a/cartographer_ros/cartographer_ros/node.h b/cartographer_ros/cartographer_ros/node.h
index 8f440fa..6384901 100644
--- a/cartographer_ros/cartographer_ros/node.h
+++ b/cartographer_ros/cartographer_ros/node.h
@@ -57,6 +57,15 @@ class Node {
   // Starts the first trajectory with the default topics.
   void StartTrajectoryWithDefaultTopics(const TrajectoryOptions& options);
 
+  // Compute the default topics for the given 'options'.
+  std::unordered_set<string> ComputeDefaultTopics(
+      const TrajectoryOptions& options);
+
+  // Adds a trajectory for offline processing, i.e. not listening to topics.
+  int AddOfflineTrajectory(
+      const std::unordered_set<string>& expected_sensor_ids,
+      const TrajectoryOptions& options);
+
   // Loads a persisted state to use as a map.
   void LoadMap(const std::string& map_filename);
 
diff --git a/cartographer_ros/cartographer_ros/offline_node_main.cc b/cartographer_ros/cartographer_ros/offline_node_main.cc
index 4034ab2..374873b 100644
--- a/cartographer_ros/cartographer_ros/offline_node_main.cc
+++ b/cartographer_ros/cartographer_ros/offline_node_main.cc
@@ -110,39 +110,9 @@ void Run(const std::vector<string>& bag_filenames) {
   }
 
   std::unordered_set<string> expected_sensor_ids;
-  const auto check_insert = [&expected_sensor_ids, &node](const string& topic) {
+  for (const string& topic : node.ComputeDefaultTopics(trajectory_options)) {
     CHECK(expected_sensor_ids.insert(node.node_handle()->resolveName(topic))
               .second);
-  };
-
-  // Subscribe to all laser scan, multi echo laser scan, and point cloud topics.
-  for (const string& topic : ComputeRepeatedTopicNames(
-           kLaserScanTopic, trajectory_options.num_laser_scans)) {
-    check_insert(topic);
-  }
-  for (const string& topic : ComputeRepeatedTopicNames(
-           kMultiEchoLaserScanTopic,
-           trajectory_options.num_multi_echo_laser_scans)) {
-    check_insert(topic);
-  }
-  for (const string& topic : ComputeRepeatedTopicNames(
-           kPointCloud2Topic, trajectory_options.num_point_clouds)) {
-    check_insert(topic);
-  }
-
-  // For 2D SLAM, subscribe to the IMU if we expect it. For 3D SLAM, the IMU is
-  // required.
-  if (node_options.map_builder_options.use_trajectory_builder_3d() ||
-      (node_options.map_builder_options.use_trajectory_builder_2d() &&
-       trajectory_options.trajectory_builder_options
-           .trajectory_builder_2d_options()
-           .use_imu_data())) {
-    check_insert(kImuTopic);
-  }
-
-  // Odometry is optional.
-  if (trajectory_options.use_odometry) {
-    check_insert(kOdometryTopic);
   }
 
   ::ros::Publisher tf_publisher =
@@ -164,8 +134,8 @@ void Run(const std::vector<string>& bag_filenames) {
       break;
     }
 
-    const int trajectory_id = node.map_builder_bridge()->AddTrajectory(
-        expected_sensor_ids, trajectory_options);
+    const int trajectory_id =
+        node.AddOfflineTrajectory(expected_sensor_ids, trajectory_options);
 
     rosbag::Bag bag;
     bag.open(bag_filename, rosbag::bagmode::Read);