HOWTO: Creating a Static Model

The are two distinct type of models in Gazebo:

Static models have their code in the main Gazebo distribution, and are statically linked into the server. Generally speaking, such models will be added by the lead developers.

Plugin models are shared objects that are loaded at runtime (like loadable modules in the Linux kernel). They are the recommended method for all new, experimental or third party models. Instructions for building plugin modules can be found here.

This page describes the basic steps for creating a static model; it describes how the source files should be laid out, how to register models with the server and how to work with GNU Autotools.

N.B. These instructions assume you are working from CVS, not a source snap-shot or distribution.

For details of how to write the contents of the model, read HOWTO: Creating a Plugin Model. Developers are also advised to read Coding Standards and Conventions before adding their model to the respository (lest I come wading through the source tree with my big red pen).

Model Source Files

Source code for models is located under server/models/, with a separate directory for each model. Model directory names should match model class names, i.e., the ExampleModel model is found the server/models/ExampleModel/ directory. Layout of files within the model directory is at the developers discretion; by convention, however, models are comprised of a single header file containing the model class declarations, and one or more source files containing the class definitions. Thus, the ExampleModel model is comprised of ExampleModel.hh and ExampleModel.cc.

The recommended way to create a new model is to copy an existing model with similar functionality, and perform some judicious search-and-replacing.

Registering the Model

Models must be registered with the server. Registration is handled by the ModelFactory class, which can be found in server/ModelFactory.cc.

Static model registration is handled by a macro defined in ModelFactory.hh:

GZ_REGISTER_STATIC("ExampleModel", ExampleModel)

The first argument gives the model name as it appears in the world file; the second argument gives the class name.

Note that static and dynamic registration macros can co-exist in the same source file, but only one of them will be used.

Working with GNU Autotools

Gazebo uses GNU Autotools to managing the build process; while Autotools can be daunting for newcomers, the rewards are well worth the effort. When using Autotools, there are two key notions to bear in mind:

Project-level configuration is controlled by configure.in found in the project top-level directory.

Module-level configuration is controlled by Makefile.am found in every sub-directory.

These configuration files are used to generate the Makefile's that will ultimately control the build process (developers should never manipulate Makefile's directly).

The basic process for adding a new model to the Autotools setup is as follows.

Create Makefile.am for the new model:
- Copy Makefile.am from another model into the new model directory.
- Modify all entries describing the model name. For example, if you copied Makefile.am from the Pioneer2AT model, replace all references to pioneer2at with examplemodel.
- Modify the SOURCES line to list the new model's source files. Be sure to include header files in this list (so they will included in the final distribution).

Modify Makefile.am in the server/models directory.
- Add the new model directory to the SUBDIRS line.

Modify configure.in in the top-level directory.
- In the ``model tests'' section, add a GAZEBO_ADD_MODEL entry for the new model. The arguments are: model name (camel caps), model path, whether or not the model should be included in the default build, a list of libraries to check for and a list of headers to check for. The model will not be built unless all of the library and header dependencies are satisfied.
- In the ``create makefiles'' section, add the path of the Makefile that needs to be created.

Re-generate the Makefile's:
- From the top-level directory, run:
```
  $ autoreconf
  $ ./configure
  
```
  with whatever arguments you would normally pass to configure.

Run make to build and link the new driver.

Last updated 12 September 2005 21:38:45