udacity-robond-p1

This repository contains my submission of the project "Build My World" to Udacity Robotics Software Engineer Nanodegree.

Contents

This project consists on a world (world/arena.world) involving:

• A building (model/slash)
• Two instances of a model created with the model editor (model/spheric_horse)
• Two instances of a model from gazebo's online model database ("cafe_table")
• A unit sphere

and the following interactions via plugins:

• Welcome (console output) (script/welcome.cpp)
• Movement of the sphere (script/move_back_and_forth{_private.hpp, .hpp, .cpp}

The plugin MoveBackAndForth is based in those that can be found in https://bitbucket.org/osrf/gazebo/src/ > (branch gazebo9) > plugins.

Instructions

Clone the repository and open a terminal in the root directory.

Building the plugins

> mkdir build && cd build
> cmake ../
> make

Usage of MoveBackAndForth plugin

This plugin will move model from <starting_position> to <ending_position> along a straight line and at a constant linear absolute speed of <speed> (m/s).

<model name='your_model'>
  <pose frame=''>1.1 2.2 3.3 4.4 5.5 6.6</pose>
  <plugin name="back_and_forth" filename="libback_and_forth.so">
    <link>link</link>
    <starting_position>1.1 2.2 3.3</starting_position>
    <ending_position>9.9 9.9 9.9</ending_position>
    <speed>2</speed>
  </plugin>
</model>

• <speed> must be in m/s
• <starting_position> is assumed to coincide with the starting position of the model, so the first three numbers in <pose> of the model should coincide with the three numbers in <starting_position>.
• if yaw, pitch and roll in initial pose of the model are 0.0, reset of the world will be handled correctly by the plugin, meaning that the model will be moved to <starting_position> with yaw, pitch and roll set to 0.0 and the movement will start from there as it should.

Loading the world

If terminal is not in the root folder, substitute $PWD by its path in all commands below.

1. Advise gazebo where to look for the plugins included in the world or model description files:

> export GAZEBO_PLUGIN_PATH=$PWD/build/script:$GAZEBO_PLUGIN_PATH

2. Do the same for the models we added:

> export GAZEBO_MODEL_PATH=$PWD/model:~/.gazebo/models:$GAZEBO_MODEL_PATH

Notice that in the case of the models, one needs to add ~/.gazebo/models along with the path where models created as part of this project are stored. The reason for this is that models included from gazebo's online model database will be downloaded into that folder, so it is necessary to let gazebo know that it should also check that directory when loading modules.

3. Load the world with gazebo:

> gazebo world/arena.world --verbose -u

The option -u starts the server in a paused state, so that one can see the initial state of the world and its elements before the plugin that moves the sphere starts working.

It is possible that the first time the world is loaded the following error shows repeatedly:

[Err] [Node.cc:105] No namespace found

This is due to the download of the models from gazebo's online model database not being finished when gazebo is already trying to find the models. If gazebo takes too long in loading after the last time the error is outputted, close it and run the last command again.

4. Click on the play button to see the sphere move along the slash. Reset of the world (Ctrl + R or Edit > Reset World) is well handled by the plugin, but initial orientation of the model might be incorrect (not a problem in the case of a sphere).

MoveBackAndForth plugin assumes that initial position of the model is exactly that specified in <starting_position>.

License

Original version of the license of this repository can be found here: https://gist.github.com/laramartin/7796d730bba8cf689f628d9b011e91d8