Error using element_type has no member named ‘imu’, what can be?

Question

I created a C++ ROS2 node that uses sensor_msgs IMU. Included the sensor_msg in the header file, also declared the IMU sensor message. Still nor really clear the error that comes. When build it I got error:

error: ‘using element_type = const struct sensor_msgs::msg::Imu_<std::allocator<void> >’ {aka ‘const struct sensor_msgs::msg::Imu_<std::allocator<void> >’} has no member named ‘imu’
  199 |   imu_q.w() = imu_msg->imu.orientation.w;

The ROS node is:

    .....
    namespace robot_perception {
    
    
    void PlaneSegmentation::onInit() {
      rclcpp::QoS qos(rclcpp::KeepLast(3));
      this->pub_plane_coeffs_ = this->create_publisher<PlaneCoefficients>(
          "output_plane_coefficients", qos);
    
      if (!this->publish_only_gd_plane_coeffs_) {
        this->pub_gd = this->create_publisher<PointCloud2>(
            "output_gd_points", qos);
        this->pub_non_gd = this->create_publisher<PointCloud2>(
            "output_non_gd_points", qos);
        this->pub_indices_ = this->create_publisher<ClusterPointIndices>(
            "output_indices", qos);
      }
    }
    
    void PlaneSegmentation::subscribe() {
      // if our pointcloud comes with normals
      if (this->is_pcd_with_normal_) {
        this->sub_cloud2_ = std::make_shared<
          message_filters::Subscriber<PointCloud2>>(
              this, "input_points");
        this->sub_imu2_ = std::make_shared<
          message_filters::Subscriber<Imu>>(this, "input_imu");
    
        this->sync_joint_ = std::make_unique<
          message_filters::Synchronizer<SyncPolicyJoint>>(this->buffer_);
        this->sync_joint_->connectInput(*sub_cloud2_, *sub_imu2_);
        this->sync_joint_->registerCallback(
            std::bind(&PlaneSegmentation::jointPcdCallback,
                      this, ph::_1, ph::_2));
      } else {  // if we get the pcd and normals separately
        this->sub_cloud_ = std::make_shared<
          message_filters::Subscriber<PointCloud2>>(this,
                                                    "input_points");
        this->sub_normal_ = std::make_shared<
          message_filters::Subscriber<PointCloud2>>(this,
                                                    "input_normals");
        this->sub_imu_ = std::make_shared<message_filters::Subscriber<
          Imu>>(this, "input_imu");
    
        this->sync_separate_ = std::make_unique<
          message_filters::Synchronizer<SyncPolicySeparate>>(this->buffer_);
        this->sync_separate_->connectInput(*sub_cloud_, *sub_normal_,
                                           *sub_imu_);
        this->sync_separate_->registerCallback(
            std::bind(&PlaneSegmentation::separatePcdCallback,
                      this, ph::_1, ph::_2, ph::_3));
      }
    }
    
    
    void PlaneSegmentation::jointPcdCallback(
        const PointCloud2::ConstSharedPtr &cloud_msg,
        const Imu::ConstSharedPtr &imu_msg) {
      std::lock_guard<std::mutex> lock(this->mutex_);
    
      PointCloudCN::Ptr point_normals(new PointCloudCN);
      pcl::fromROSMsg(*cloud_msg, *point_normals);
    
      // split PointCloudCN pcd into separate pts pcd & normals pcd
      PointCloudC::Ptr cloud(new PointCloudC);
      PointCloudN::Ptr normals(new PointCloudN);
      backhoe::pcl_utils::splitPointsAndNormals(cloud, normals, point_normals);
    
      this->extractGroundPlane(cloud, normals, imu_msg, cloud_msg->header);
    }
    
    
    void PlaneSegmentation::separatePcdCallback(
        const PointCloud2::ConstSharedPtr &cloud_msg,
        const PointCloud2::ConstSharedPtr &normal_msg,
        const Imu::ConstSharedPtr &imu_msg) {
      std::lock_guard<std::mutex> lock(this->mutex_);
    
      // convert cloud and normals from ROS msgs
      PointCloudC::Ptr cloud(new PointCloudC);
      pcl::fromROSMsg(*cloud_msg, *cloud);
    
      PointCloudN::Ptr normals(new PointCloudN);
      pcl::fromROSMsg(*normal_msg, *normals);
    
      this->extractGroundPlane(cloud, normals, imu_msg, cloud_msg->header);
    }
    
    /**
     * Extract ground plane from input pcd+normals, based on the input imu.
     
     */
    void PlaneSegmentation::extractGroundPlane(
        const PointCloudC::Ptr cloud,
        const PointCloudN::Ptr normals,
        const Imu::ConstSharedPtr &imu_msg,
        const Header header) {
      RCLCPP_INFO(this->get_logger(), "Starting ground plane extraction");
    
      // convert imu message to eigen quaternion
      Eigen::Quaternionf imu_q;
      Imu imu;
      imu_q.w() = imu_msg->imu.orientation.w;
      imu_q.x() = imu_msg->imu.orientation.x;
      imu_q.y() = imu_msg->imu.orientation.y;
      imu_q.z() = imu_msg->imu.orientation.z;
      ....

I also included #include <sensor_msgs/msg/imu.hpp> in the header file. Still dont understand where the error is from. Any help?

score 2 · Accepted Answer · answered Oct 12 '22 at 15:08

The error says that the IMU message does not contain the field imu. Have a look at the API then you'll also see that no such member exists.

Instead, the sensor_msgs::msg::Imu exposes directly the orientation, so what you need to do is for example:

static void imu_callback(const sensor_msgs::msg::Imu::SharedPtr msg) {
  RCLCPP_INFO(
      rclcpp::get_logger("rclcpp"), "Got IMU msg with WXYZ: [%f, %f, %f, %f]",
      msg->orientation.w, msg->orientation.x, msg->orientation.y,
      msg->orientation.z);
}

Error using element_type has no member named ‘imu’, what can be?

1 Answers1