/** @page libgazebo_usage Using libgazebo
External programs can use libgazebo to interact with the Gazebo
simulator. libgazebo is a simple C library that allows other programs
to peek and poke into a running simulation; through this library,
programs may read sensor data from and send commands to simulated
devices. The Player device server, for example, uses libgazebo in
this way.
Normal users will interact with Gazebo via player and need not be
aware of this library. This chapter is included primarily to aid
those who either wish to add a new type of interface to the simulator,
or who wish to write their own custom control programs (by-passing
player entirely).
Python bindings for libgazebo are also @ref libgazebo_py "available".
@section libgazebo_arch Architecture
libgazebo uses interprocess communication (IPC) to allow a program to
exchange data with a running simulator. Hereafter, we shall refer to
the simulator as the server and the program as the
client. Thus, for example, when using player to interact with
Gazebo, Gazebo is the server and player is the client.
The details of the underlying IPC are entirely hidden by libgazebo,
which should be treated as a black box for passing data back and forth
to the server. Currently, the only limitation users need be aware of
is that both server and client must reside on the same machine; they
cannot be run in separate locations across a network.
@section libgazebo_devices Devices and Interfaces
libgazebo makes the familiar distinction between devices and
interfaces. In Gazebo, a device is a fully
parameterized model, representing a particular real-world object such
as a Pioneer2AT robot or a SICK LMS200 laser. An interface, on the
other hand, is a general specification for an entire class of devices,
such as position or laser. Thus, a Pioneer2AT device
will present a position interface, while the SICK LMS200 will
present a laser interface.
The complete set of interfaces supported by libgazebo is described
@ref libgazebo "here". Note that these interfaces should not be
confused with the interfaces defined by Player. Currently, these two
sets of interfaces are fairly similar, but there is no guarantee that
they will remain so in future.
@section libgazebo_using Using libgazebo
Client programs must connect both to a specific server and a specific
set of devices within that server. The following code snippet
illustrates the general behavior:
@include simple.c
There are several points to note:
- The value of server_id variable must correspond to the
server ID specified on the Gazebo command line. By default, the ID
is 0, but other values may be specified if the user is
running multiple instances of Gazebo simultaneously.
- The value of client_id variable must be unique for each
client, and bounded in the range GZ_CLIENT_ID_FIRST to
GZ_CLIENT_ID_LAST.
- The device_id variable specifies a unique device ID; the
value of this variable must correspond to the device ID specified in
the Gazebo world file.
- Any attempt to connect to a device using an unsupported interface
will result in the open function returning an error. For
example, if the device specified by device_id is actually
a laser, attempting to open it using gz_position_open()
will result in an error.
- Do not use the create and destroy functions
associated with each interface; these are reserved for use by Gazebo
only. Use open and close instead.
This example can be demonstrated using the follow world file:
@include simple.world
@section libgazebo_building Compiling and Linking Programs With libgazebo
All public functions are declared in gazebo.h and defined in
libgazebo.a. The default install scripts put these in sensible
places, so your compiler should pick them up automatically. Nevertheless,
the @b recommended way to build applications is using the @c pkg-config
mechanism; the compile and link lines should look something like this:
@verbatim
gcc -Wall -g3 `pkg-config --cflags gazebo` -c -o simple.o simple.c
gcc simple.o -o simple `pkg-config --libs gazebo`
@endverbatim
*/