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### Can't change gravity in world-file

I'm new to Gazebo and SDF-files in general. The file I'm using works, but when I try to specify gravity to it, I get an error.

I get the following error when trying to change the gravity using a SDF file.

Warning [parser.cc:750] XML Element[gravity], child of element[world] not defined in SDF. Ignoring[gravity]. You may have an incorrect SDF file, or an sdformat version that doesn't support this element.


My SDF-file looks like this;

<?xml version="1.0" ?>
<sdf version="1.5">
<world name="default">
<gravity>0 0 -0.1</gravity>
<scene>
<origin_visual>0</origin_visual>
<grid>0</grid>
</scene>
<physics type="ode">
<max_step_size>0.003</max_step_size>

<!-- Run as fast as possible -->
<real_time_update_rate>0.0</real_time_update_rate>
<ode>
<constraints>
<!-- Simulator.cpp -->
<erp>0.1</erp>
<cfm>10e-6</cfm>

<!-- Making this smaller seems to decrease rather than increase stability. -->
<contact_max_correcting_vel>100</contact_max_correcting_vel>
<contact_surface_layer>1e-8</contact_surface_layer>
</constraints>
<solver>
<type>quick</type>
</solver>
</ode>
</physics>

<!-- A global light source -->
<include>
<uri>model://sun</uri>
</include>
<include>
<uri>model://tol_ground</uri>
</include>

<plugin name="tol-control" filename="libtolworldcontrol.so" />
</world>
</sdf>


Any ideas why it says that SDF might not have this element defined?