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FAQ

Interaction with Tensorflow

If your Python application imports both scenario and tensorflow, you might experience segfaults with no error messages. Likely the problem is the protobuf library. In fact, both Tensorflow and Ignition Gazebo link agains protobuf, but while Gazebo uses the default version of your OS, Tensorflow vendors a more recent version. If you import scenario before tensorflow, the system protobuf is loaded, and Tensorflow will segfault.

The only workaround we found is importing Tensorflow first:

>>> import tensorflow
>>> import scenario.bindings.gazebo

Ogre2 and OpenGL

On GNU/Linux distributions that ship an old OpenGL version, the GUI could fail to open printing error like Unable to create the rendering window. The reason is that Ignition Gazebo has ogre-next (also known as ogre2) as default rendering engine, and it requires OpenGL greater than 3.3. You can find more details here.

The workaround we recommend is modifying the file ~/.ignition/gazebo/gui.config as follows:

--- .ignition/gazebo/gui.config 2020-06-04 14:41:33.471804733 +0200
+++ .ignition/gazebo/gui.config 2020-06-04 14:42:47.826475035 +0200
@@ -30,7 +30,7 @@
     <property type='bool' key='showTitleBar'>false</property>
     <property type='string' key='state'>docked</property>
   </ignition-gui>
-  <engine>ogre2</engine>
+  <engine>ogre</engine>
   <scene>scene</scene>
   <ambient_light>0.4 0.4 0.4</ambient_light>
   <background_color>0.8 0.8 0.8</background_color>

After this modification, world SDF files that do no specifically ask ogre2 will use ogre as default rendering engine which works also with older OpenGL versions.

Default SDF world

If not specified differently, the :cpp:class:`~scenario::gazebo::GazeboSimulator` class uses a default world file that is completely empty, without even the ground plane. You can load a custom SDF world using :cpp:func:`~scenario::gazebo::GazeboSimulator::insertWorldFromSDF()` and then extracting it from the simulator with :cpp:func:`~scenario::gazebo::GazeboSimulator::getWorld()` using its name.

<?xml version="1.0" ?>
<sdf version="1.7">
    <world name="default">
        <physics default="true" type="dart">
        </physics>
        <light type="directional" name="sun">
            <cast_shadows>true</cast_shadows>
            <pose>0 0 10 0 0 0</pose>
            <diffuse>1 1 1 1</diffuse>
            <specular>0.5 0.5 0.5 1</specular>
            <attenuation>
                <range>1000</range>
                <constant>0.9</constant>
                <linear>0.01</linear>
                <quadratic>0.001</quadratic>
            </attenuation>
            <direction>-0.5 0.1 -0.9</direction>
        </light>
    </world>
</sdf>

Note

If you don't specify any GUI configuration, the default ~/.ignition/gazebo/gui.config is used. This is the preferred approach since it's easier to maintain and keep world files updated. You can find more information in the upstream default.sdf.

Tip

You don't need to add the physics plugin in the world file. You can use :cpp:func:`scenario::gazebo::World::setPhysicsEngine()` from your code. You can also load other plugins during runtime using :cpp:func:`scenario::gazebo::World::insertWorldPlugin()` and :cpp:func:`scenario::gazebo::Model::insertModelPlugin()`.