7.31 passthrough

Authors

Brian P. Gerkey gerkey(at)stanford.edu

Synopsis

The passthrough driver acts as a client to another Player server; it returns data generated by the remote server to client programs, and send commands from the client programs to the remote server. In this way, one Player server can pretend to have devices that are actually located at some other location in the network (i.e., owned by some other Player server). Thus, the passthrough driver makes possible two important capabilities:

• Data from multiple robots can be aggregated in a single Player server; client programs can then talk to more than one robot through a single connection.
• Computationally intensive drivers can be moved off the robot and onto a workstation. Client programs connect to the workstation rather that the robot, but are otherwise unchanged.

See the below for some examples of the passthrough driver in action.

Interfaces

The passthrough driver will support any of Player's interfaces, and can connect to any Player device.

Configuration file options

Name Type Default Meaning

host string localhost Host name for the machine running the remote Player server.

port integer 6665 Port number for remote server.

index integer 0 Index of the device on the remote server.

Example: Controlling multiple robots through a single connection

The passthrough driver can be used to aggregate devices from multiple robots into a single server. The following example illustrates the general method for doing

• Imagine that we have to robots named bee and bug. On each robot, start a Player server with the following configuration file:

    position:0 (driver "p2os_position")
    laser:0 (driver "sicklms200")
  

  In this example, the robots are assumed to be Pioneer's with SICK laser range-finders.
• Now imagine that we have a workstation named orac. On this workstation, start another instance of Player with the following configuration file:

    position:0 (driver "passthrough" host "bee" port 6665 index 0)
    laser:0 (driver "passthrough" host "bee" port 6665 index 0) 
    position:1 (driver "passthrough" host "bug" port 6665 index 0)
    laser:1 (driver "passthrough" host "bug" port 6665 index 0)
  

  A client connecting to orac will see four devices: two position devices and two laser devices. Both robots can now be controlled through a single connection to orac.

Example: Shifting computation

Computationally expensive drivers (such as adaptive_mcl) can be shifted off the robot and onto a workstation. The basic method is a straight-forward variant of the example given above.

• Imagine that we have a robot named bee. On bee, run the Player server with this configuration file:

    position:0 (driver "p2os_position")
    laser:0 (driver "sicklms200")
  

  The robot is assumed to be a Pioneer with a SICK laser range-finder.
• Now imagine that we have a workstation named orac. On this workstation, start another instance of Player with the following configuration file:

    position:0 (driver "passthrough" host "bee" port 6665 index 0)
    laser:0 (driver "passthrough" host "bee" port 6665 index 0) 
    localize:0 (driver "adaptive_mcl" position_index 0 laser_index 0 ...)
  

  (see Section 7.3 for a detailed description of the additional setings for the adaptive_mcl driver). Clients connecting to this server will see a robot with position, laser and localize devices, but all of the heavy computation will be done on the workstation.

Example: Using the adaptive_mcl driver with Stage

Some newer drivers, such as the adaptive_mcl driver, are not supported natively in Stage. For these drivers users must employ a second Player server configured to use the passthrough driver. The basic procedure is as follows.

• Start Stage with a world file something like this:

    ...
    position (port 6665 laser ())
    ...
  

  Stage will create one robot (position device) with a laser, and will start a Player server that listens on port 6665.
• Start another Player server using the command

    player -p 7000 amcl.cfg
  

  where the configuration file amcl.cfg looks like this (see Section 7.3 for a detailed description of the setings for the adaptive_mcl driver):

    position:0 (driver "passthrough" port 6665 index 0)
    laser:0 (driver "passthrough" port 6665 index 0) 
    localize:0 (driver "adaptive_mcl" position_index 0 laser_index 0 ...)
  

  The second Player server will start up and listen on port 7000; clients connecting to this server will see a robot with position, laser and localize devices.