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I got a DDS-system(OMG DDS) who's communicating with a ROS-node over radio. The information being received is a struct with velocity, state, longitude, latitude etc. This works well, and my DDS-client has no problem printing the information being transmitted from the node over the radio. Now, I've got a GUI-application written in Qt, who creates models and puts them on a predefined map. These modelse have defined set-information functions, which when triggered updates the map to give a smooth visualisation of the information it receives.

Now here is problem, I've no idea how to make the GUI application communicate with my DDS-client. I would rather not intertwine these two, since I've had enough trouble just making the DDS-client and sender work and compile with ROS. Ive though about a separate queue system, which can be included in the DDS-client and the GUI application, but I dont know if this could work. Ive also though about writing a SQL database, and then push new data, and pull new data when it is detected in my GUI application. Some sort of on_data_available function which triggers the pull-function. Ive heard the last one is a bad idea, since I'm working with only one set of data which is being continuously updated (the model represents one USV), and a database is then considered overkill, but I would love to get inputs here.

Im sorry if this isn't sufficient information, I can't really provide code examples for different reasons. If anyone have any inputs, shout out, would love to hear them. And if I'm not being specific enough, ill try to rewrite it as best as i can.

Hawken
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I've no idea how to make the GUI application communicate with my DDS-client

Your question is not specific to DDS or your GUI application -- you essentially ask for a simple and convenient inter-process communication (IPC) mechanism. As you can see when you follow the link, there are loads of different options.

Given that you already have your data as well as the associated type definitions available in DDS, I suspect that using DDS for this task would still be the easiest way to go. You could set it up to communicate over shared memory or local loopback. DDS will do all discovery and communication under the hood, including (cross-language) de/serialization. If you choose a different mechanism, you might end up doing more work yourself.

As an alternative, some DDS implementations (commercially) support native integration with SQL databases. Those will introspect the DDS data definitions and create all required tables for you. Updates from DDS are automatically forwarded to the database, and vice-versa. You could feed your GUI off of that database.

Reinier Torenbeek
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