About timestamp synchronization

[codehory]

In ros_calib_init.cpp,

    /// Handle Lidar measurement
    sensor_msgs::PointCloud2::ConstPtr s_lidar = m.instantiate<sensor_msgs::PointCloud2>();
    if (s_lidar != nullptr && m.getTopic() == topic_lidar) {
        lin_core::VPointCloud::Ptr cloud_pcl(new lin_core::VPointCloud);
        pcl::fromROSMsg(*s_lidar, *cloud_pcl);
        LOdom->feedScan((*s_lidar).header.stamp.toSec(), cloud_pcl);
        LOdom->append_and_update(true);
        Eigen::Matrix3d deltaR_L = LOdom->get_latest_relativePose().odometry_ij.block(0, 0, 3, 3);
        Eigen::Quaterniond delta_qL(deltaR_L);
        geometry_msgs::PoseStamped pose;
        pose.header.stamp = s_lidar->header.stamp;
        pose.pose.orientation.x = delta_qL.x();
        pose.pose.orientation.y = delta_qL.y();
        pose.pose.orientation.z = delta_qL.z();
        pose.pose.orientation.w = delta_qL.w();
        lodom_publisher.publish(pose);
        **imupacket.header.stamp = s_lidar->header.stamp;**
        imu_packet_publisher.publish(imupacket);
        imupacket.stamps.clear();
        imupacket.accelreadings.clear();
        imupacket.gyroreadings.clear();
    }

I don't understand why "imupacket.header.stamp = s_lidar->header.stamp". Why not use the timestamp of IMU?

[codehory]

topic: /imu_packet

header: seq: 38 stamp: secs: 1618587129 nsecs: 856979200 frame_id: '' stamps:

secs: 1618587129        //   start
nsecs: 894484179

......

secs: 1618587129       //   end
nsecs: 976984179

header: seq: 39 stamp: secs: 1618587129 nsecs: 956735488 frame_id: ''

why the last timestamp of 38 is later than the timestamp of 39 ？

[liang0724s]

@codehory Hi, did you run it successfully? What's your version of Ubuntu and pcl? I met an error: (gdb) Program received signal SIGSEGV, Segmentation fault. Undefined command: "Program". Try "help". (gdb) 0x00007ffff2bdddc4 in long double boost::math::lanczos::lanczos17m64::lanczos_sum(long double const&) () from /usr/local/lib/libpcl_io.so.1.9

[SubMishMar]

I don't get the question about time sync but I discovered that https://github.com/koide3/ndt_omp works ok on newer ubuntu and pcl. I have added a slightly modified version in the repository itself.