OpenCPN to display LIDAR based SLAM for autonomous Navigation

[Baltic_Tobi]

Hello everyone,
I am glad to have found this great forum to address a question to the OpenCPN specialists among you.

I am working on autonomous navigation of maritime vehicles in limited areas.
For this I use a LIDAR configured as a ROS node and Google Cartographer to create a map.
I would like to display this map as an overlay in OpenCPN.

Can you give me some hints on which options are suitable?
Preferably I would like to send a UDP message over the network to OpenCPN, similar to what is done with the Radar PI plugin.
Possibly I can use the Radar PI plugin directly?
Where can I find the specification for the structure of the UDP message?

I would like to display lines, points or polygons in different color and transparency.
As with a radar image, the elements also need to be deleted/changed later.

As an alternative: Is there a possibility to read the overlay continuously repeated from a file that is updated by another program?

I am very interested in your suggestions?

Many greetings
Baltic_Tobi

[rgleason]

Baltic wrote:

For this I use a LIDAR configured as a ROS node and Google Cartographer to create a map.

I would like to display this map as an overlay in OpenCPN.

Response:
Why not use Opencpn to display the typical enc or rnc charts that are readily available?

Then use Lidar to help with navigation?

What formats can your lidar "map" be in? Mbtiles might be useful as opencpn can overlay that, also jpeg, png and the other image formats (look at weatherfax plugin and photo---.plugin

[Baltic_Tobi]

Hi rgleason, thanks for your suggestions so far.

Originally Posted by rgleason

Why not use Opencpn to display the typical enc or rnc charts that are readily available?

Of course, I do so.

Originally Posted by rgleason

Then use Lidar to help with navigation?

Yes, and I want to view the LIDAR measurement information for monitoring and debugging.

Originally Posted by rgleason

What formats can your lidar "map" be in?

I need to check the export options of Google Cartographer:
https://google-cartographer-ros.read...ts_writer.html

Otherwise I will have to build my own interface.

Originally Posted by rgleason

Mbtiles might be useful as opencpn can overlay that, also jpeg, png and the other image formats (look at weatherfax plugin and photo---.plugin

The LIDAR-map data has to update at least every second like a radar measurment. Is this possible with Mbtiles and images?

[Canne]

Originally Posted by Baltic_Tobi

<snip>The LIDAR-map data has to update at least every second like a radar measurment. Is this possible with Mbtiles and images?</snip>

Maybe, but for the speed you may want to avoid the filesystem and build your volatile map sweeps in CPU or GPU memory and draw them as an overlay on the map using OpenGL: for that purpose, the radar_pi is indeed the one you want to fork, see this line in it. In one of the overlay drawing modules of my own I draw quite complex, radar-like sweeping lines at 1Hz with OpenGL. All that passes on the GPU, the CPU load needle barely moves. I map lines on the chart using Mercator-functions in the OpenCPN API. Good luck to your project, how interesting!

[bcn]

Originally Posted by Baltic_Tobi

Hello everyone,
I am glad to have found this great forum to address a question to the OpenCPN specialists among you.

I am working on autonomous navigation of maritime vehicles in limited areas.
For this I use a LIDAR configured as a ROS node and Google Cartographer to create a map.
I would like to display this map as an overlay in OpenCPN.

Can you give me some hints on which options are suitable?
Preferably I would like to send a UDP message over the network to OpenCPN, similar to what is done with the Radar PI plugin.
Possibly I can use the Radar PI plugin directly?
Where can I find the specification for the structure of the UDP message?

I would like to display lines, points or polygons in different color and transparency.
As with a radar image, the elements also need to be deleted/changed later.

As an alternative: Is there a possibility to read the overlay continuously repeated from a file that is updated by another program?

I am very interested in your suggestions?

Many greetings
Baltic_Tobi

What type of LiDAR you are planning to use? Rotating 360 degree like the Velodyne or solid state LiDAR like the Livox one? I suppose you want single return. Range 100m? What precision and accuracy do you need? Heading and perhaps the complete attitude will be interesting. Curious to see outputs running from a rolling platform and returns from sea or spray.
Interesting project..
Keep us informed about - also intermediate - results.

[rgleason]

Of course Petri [canne] is right!

[Baltic_Tobi]

Originally Posted by bcn

What type of LiDAR you are planning to use? Rotating 360 degree like the Velodyne or solid state LiDAR like the Livox one? I suppose you want single return. Range 100m? What precision and accuracy do you need? Heading and perhaps the complete attitude will be interesting. Curious to see outputs running from a rolling platform and returns from sea or spray.
Interesting project..
Keep us informed about - also intermediate - results.

We use multiple Velodyne LIDARs. You are right. The measurement of the lidar is fused with the measurement of an IMU to compensate for the movements of the ship.

I just want to display the result of the data processing of the Lidar in opencpn, i.e. the SLAM based map from google cartographer.

Is there any documentation of the radar plug in interface? I need to know how to pack the UDP messages. I found
https://github.com/opencpn-radar-pi/...icoReceive.cpp
but some explanations would be fine.

[Douwe Fokkema]

Originally Posted by Baltic_Tobi

We use multiple Velodyne LIDARs. You are right. The measurement of the lidar is fused with the measurement of an IMU to compensate for the movements of the ship.

I just want to display the result of the data processing of the Lidar in opencpn, i.e. the SLAM based map from google cartographer.

Is there any documentation of the radar plug in interface? I need to know how to pack the UDP messages. I found
https://github.com/opencpn-radar-pi/...icoReceive.cpp
but some explanations would be fine.

Sorry for my late reaction, I was traveling.

The radar_pi plugin consists of a back-end and a front-end. The back-end contains all the radar type independent functions, such as the display handling, alarm handling, ARPA, and trails. The front-end contains the radar specific functions. These are the receiving parts and the radar control, the commands to the radar. If we can consider a Lidar as a new radar type, a Lidar_receive.cpp and a Lidar_control.cpp will have to be made. The Lidar_receive.cpp should take care of the radar address handling, and receives the incoming UDP messages. Some of the messages received will be control messages, giving feedback on the settings of the radar. Image information is in messages containing so called radar spokes. A radar spoke is an array of values representing the intensities of the radar returns at an indicated angle and heading. The imaging interface from the receive function to the back-end is implemented by a call ProcessRadarSpoke, passing (a pointer to) the array of intensities, the heading at time of receiving, the relative bearing of the spoke and the time of receiving the spoke. Later in the process the time of receiving the spoke is used to determine the position of the radar at receiving time so that the spoke can be drawn at the right location on the chart. So the radar image as drawn by the back-end is not a complete radar image drawn at the current location. Instead, each individual spoke is drawn at the position at which it was received. For a moving vessel this makes quite some difference at short range. To predict the positions of receiving the spokes (always after the last received GPS position) a Kalman filter is used.

If you have more specific questions that are beyond the scope of this forum, you can mail me at df at percussion.nl.

Douwe Fokkema