How can I use the $GPRMC data from INS with Hesai PandarXT32 Lidar data to run SLAM in matlab

Hello, I hope everyone is doing well. I have loaded my pcap data from the Hesai Pandar32XT into Matlab using the "hesaiFileReader" in matlab. Following this, I have put every single pointcloud extracted into a matrix of its own using this loop:

And alongside that, I have my INS log files in the $GPRMC format. Therefore, I was wondering, how can I combine these two pieces of information and then run the SLAM algorithim using them in MatLAB? Is there a library to interpret INS data in MatLAB and run SLAM with the provided pointclouds? Also, I have one concern as well. It seems the PandarXT32 does not save the UNIX time; rather it only stores the runtime in seconds (see image below)

So I was wondering, how can I also sync this data with the INS if it is possible.

I really appreciate your help, have a great day. Thanks!

Answer 1

[Maneet Kaur Bagga]

Hi Dave,

As per my understanding, to physically send the $GPRMC NMEA message via serial to the Hesai the timestamps should end up in absolute time, and not time since you have powered up the system.

The internal 1 Hz signal will be locked to the PPS. Each rising edge still trigers a GPS Data Packet. Meanwhile, the Lidar will extract the actual date and time from the NMEA messages ($GPRMC or $GPGGA) and stamp them into both Point Cloud. Therefore the current data cannot be converted to absolute time to run SLAM unless you can find the offset between your data and GPS time.

Hope this helps!