'#pragma once' equivalent for urdf/xacro files

asked 2018-10-03 15:55:56 -0500

Julian98
69 ●5 ●9 ●13

I have multiple urdf files representing different components of a robot. As I don't want to define materials multiple times in different files, I created a file containing those definitions ('materials.urdf.xacro'). The file looks like this:

<?xml version="1.0"?>

<robot>

    <material name="Black">
        <color rgba="0.0 0.0 0.0 1.0"/>
    </material>

    <material name="Blue">
        <color rgba="0.0 0.0 0.8 1.0"/>
    </material>

    <material name="Green">
        <color rgba="0.0 0.8 0.0 1.0"/>
    </material>

    <material name="Grey">
        <color rgba="0.2 0.2 0.2 1.0"/>
    </material>

    <material name="DarkGrey">
        <color rgba="0.1 0.1 0.1 1.0"/>
    </material>

    <material name="Orange">
        <color rgba="${255/255} ${108/255} ${10/255} 1.0"/>
    </material>

    <material name="Brown">
        <color rgba="${222/255} ${207/255} ${195/255} 1.0"/>
    </material>

    <material name="Red">
        <color rgba="0.8 0.0 0.0 1.0"/>
    </material>

    <material name="White">
        <color rgba="1.0 1.0 1.0 1.0"/>
    </material>

</robot>

I include them via

<xacro:include filename="$(find package_name)/urdf/materials.urdf.xacro" />

in a component file ('laser.urdf.xacro') and in the robot definition file ('robot.urdf.xacro') with itself includes 'laser.urdf.xacro').

When I try to run the urdf file via rviz, I get an error:

material 'Black' is not unique.

I presume it's due to the indirect second include of the 'materials.urdf.xacro' file, just like the problems you would have in C++ without '#pragma once' or the '#ifndef ... => #define ... => #endif' construct.

So is there an equivalent to this in urdf/xacro files?

ROS Kinetic
Ubuntu 16.04

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answered 2018-10-04 01:46:57 -0500

Delb

3907 ●16 ●105 ●68

I'm not aware of this kind of workaround and it doesn't seem possible.

What you can do is instead of having multiple <xacro:include ..../> tags in all of your urdf files is to can create a new file like standalone.urdf.xacro (i usually do my_robot_name_standalone.urdf.xacro) and inside it you only use the <xacro:include../> to add all of your urdf files (which have no includes anymore). With that you ensure to avoid multiple inclusions. Here's an exemple :

<?xml version="1.0"?>
<robot name="my_robot"
       xmlns:sensor="http://playerstage.sourceforge.net/gazebo/xmlschema/#sensor"
       xmlns:controller="http://playerstage.sourceforge.net/gazebo/xmlschema/#controller"
       xmlns:interface="http://playerstage.sourceforge.net/gazebo/xmlschema/#interface"
       xmlns:xacro="http://ros.org/wiki/xacro">

  <xacro:include filename="$(find my_robot_description)/urdf/common_properties.urdf.xacro" />
  <xacro:include filename="$(find my_robot_description)/urdf/my_robot.urdf.xacro" />
</robot>

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FYI: the playerstage stuff is not needed any longer.

gvdhoorn ( 2018-10-04 01:49:50 -0500 )edit

Okay I didn't know that, thank you.

Delb ( 2018-10-04 01:52:03 -0500 )edit

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answered 2018-10-04 01:37:59 -0500

gvdhoorn
86574 ●283 ●1432 ●1054 http://cor.tudelft.nl/

updated 2018-10-04 01:41:19 -0500

I presume it's due to the indirect second include of the 'materials.urdf.xacro' file, just like the problems you would have in C++ without '#pragma once' or the '#ifndef ... => #define ... => #endif' construct.

So is there an equivalent to this in urdf/xacro files?

Not that I know of.

Personally I work around this by using "anonymous" materials and using a macro to create them. See here for an example.

It's actually an error from the URDF parser, not xacro itself (it doesn't care).

You may also want to look into namespace support in xacro.

Edit: I've never tried it, but perhaps the conditional support in xacro can now prevent pieces of xacro from being evaluated. You could use that to wrap everything in a xacro:if and then set a xacro:property inside the body.

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'#pragma once' equivalent for urdf/xacro files

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