iviz_msgs_gen is the module in charge of generating C# files from the messages in the ros_msgs folder. If you have a new message type that you want to use with iviz_roslib, just copy the package folder into ros_msgs and run this project.
You can either:
- Open the .csproj file in your favorite C# editor, and hit Run.
- Open a console, go to this folder, and run the following command:
dotnet run -c Release