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# strange pitch direction

Hello! I have some troubles understanding rpy. Here is my simple URDF file:

<robot name="test">
<inertial>
<mass value="4.0" />
<origin xyz="1 0 0"/>
<inertia ixx="1" ixy="1" ixz="1" iyy="1" iyz="1" izz="1" />
</inertial>
<visual>
<geometry>
<box size="0.1 0.02 0.02"/>
</geometry>

</visual>

<inertial>
<mass value="4.0" />
<origin xyz="1 0 0"/>
<inertia ixx="1" ixy="1" ixz="1" iyy="1" iyz="1" izz="1" />
</inertial>
<visual>
<geometry>
<box size="0.1 0.02 0.02"/>
</geometry>

</visual>

<joint name="j1" type="revolute" >
<origin xyz="0.1 0 0" rpy="0 -0.5 0" />
<axis xyz="1 0 0"/>
<limit lower="-1.57" upper="1.57" effort="10" velocity="10"/>
</joint>

</robot>


As you see, there are two links with a revolute joint between them. There is a pitch of -0.5 radians in the joint. And here is the rviz image :

The question is why link1 is rotated upwards instead of downwards?

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You specify a pitch of -0.5 rads, this is a rotation around the y axis. The y axis is denoted in green. As (by convention) a right handed frame is used, you can use the right-hand rule to determine the direction or rotation. From what I can tell, the rotation on the picture is correct.

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