faq.html

  carmen_ipc_initialize(argc, argv);
  carmen_param_check_version(argv[0]);

  /* Tell the first simulator about the second */ 

  carmen_simulator_connect_robots("localhost:1382");

  /* Connect to the second IPC context, assumed to be running on
     localhost:1382 */

  IPC_connectModule(argv[0], "localhost:1382");

  /* Tell the second simulator about the first. */ 

  carmen_simulator_connect_robots("localhost");

  return 0;
}
@endverbatim


Position the first robot (using the first \c navigator_panel). Position
the second robot (using the second \c navigator_panel) so that it is a
little bit in front of where you put the first robot (which of course you
can't see in the second \c navigator_panel) and pointing back at the first
robot. If you start two instances of \c robotgraph, you should see the
other robot in each robotgraph. As you drive the robots around, they should
interfere with each other and see each other, just as if they were physically
there. 

@section faq_f How can I control multiple robots in a multi-robot simulation?

The first thing is to get both simulations working, as described above.

The next thing is to understand multiple IPC contexts, reading the IPC
manual. 

When you subscribe to (most) IPC messages, you set up a handler (and maybe
message pointer) on a context-specific basis (although you only get one
handler and message allocation per context). 

So, if you wanted to navigation status messages from two simulations, you
could use the following:
@verbatim
void connect_to_two_simulations(char *simulation1, char *simulation2,
                                IPC_CONTEXT_PTR *context1,
                                IPC_CONTEXT_PTR *context2) 
{

  *context1 = IPC_connectModule(module_name, simulation1);
  carmen_navigator_subscribe_status(NULL, handler1, CARMEN_SUBSCRIBE_NOW);

  *context2 = IPC_connectModule(module_name, simulation2);
  carmen_navigator_subscribe_status(NULL, handler2, CARMEN_SUBSCRIBE_NOW);

  IPC_setContext(*context1);
  carmen_navigator_set_goal_place("lab door");
  carmen_navigator_go();

  while (1) {
    IPC_setContext(*context1);
    sleep_ipc(1);
    IPC_setContext(*context2);
    sleep_ipc(1);
  } 
}
@endverbatim 

What this does is establish a connection with a simulation running on the
\c CENTRALHOST described by simulation1, and a simulation running on
\c CENTRALHOST described by simulation2. (The simulations presumably were
connected earlier.) The function subscribes to navigator status messages from
each simulation, using different handlers for each message. You could
certainly handle messages from both simulations using the same function, using
the \c IPC_CONTEXT_PTR IPC_getContext(); function inside the handler to
tell which simulation generated the callback. 

After the callbacks are established, the function goes back to the IPC context
of the first simulation, sets a goal and starts the robot moving. After that,
the function indefinitely just handles messages.

**/

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