xacro4sdf 1.2.2

a simple XML macro script for sdf, like ros/xacro which is desiged for urdf.

xacro4sdf

a simple python script to define and parse XML macro for sdf (sdformat), like ros/xacro which is desiged for urdf.

Reference: ros/xacro

With Xacro, you can construct shorter and more readable XML files by using macros that expand to larger XML expressions.

xacro4sdf is incompatible with xacro API(ros/xacro)

1. Example and Usage

Install

#install by pip
pip install xacro4sdf 
# or install from source code
# git clone https://github.com/gezp/xacro4sdf.git
# cd xacro4sdf && sudo python3 setup.py install

create model.sdf.xacro file (test/model.sdf.xacro)

<?xml version="1.0"?>
<sdf version="1.7">
    <xacro_define_property name="rplidar_a2_h" value="0.2" />
    <xacro_define_macro name = "rplidar_a2_collision_and_visual" params="prefix">
        <collision name="${prefix}_collision">
            <xacro_macro name="geometry_mesh" uri="model://rplidar_a2/meshes/rplidar_a2.dae"/>
        </collision>
        <visual name="${prefix}_visual">
            <xacro_macro name="geometry_mesh" uri="model://rplidar_a2/meshes/rplidar_a2.dae"/>
        </visual>
    </xacro_define_macro>
    <!--rplidar a2-->
    <model name='rplidar_a2'>
        <link name="link">
            <inertial>
                <pose>0 0 0.02 0 0 0</pose>
                <xacro_macro name="inertia_box" m="0.5" x="${rplidar_a2_h}" y="${rplidar_a2_h+0.1}" z="${2*rplidar_a2_h}"/>
            </inertial>
            <xacro_macro name="rplidar_a2_collision_and_visual" prefix="rplidar_a2"/>
        </link>
    </model>
</sdf>

• the macro of inertia_box is pre-defined in common.xacro (refer to 2.5 pre-defined common.xacro)

run

xacro4sdf model.sdf.xacro

• it will generate model.sdf (the result should be same as test/model.sdf)
• more examples can be found test folder.

2. Features

• Properties
• Macros
• Math expressions
• Include

2.1. Properties

Properties are named values that can be inserted anywhere into the XML document

xacro definition

<!--definition of properties -->
<xacro_define_property name="radius" value="4.3" />
<!--use of properties-->
<circle diameter="${2 * radius}" />

generated xml

<circle diameter="8.6" />

2.2. Macros

The main feature of xacro4sdf is macros.

Define macros with the macro tag <xacro_define_property>, then specify the macro name and a list of parameters. The list of parameters should be whitespace separated.

The usage of Macros is to define <xacro_macro> which will be replaced with <xacro_define_property> block according to the param name.

xacro definition

<!--definition of macro-->
	<xacro_define_property name="mass" value="0.2" />
	<xacro_define_macro macro_name="box_inertia" params="m x y z">
        <mass>${m}</mass>
        <inertia>
            <ixx>${m*(y*y+z*z)/12}</ixx>
            <ixy>0</ixy>
            <ixz>0</ixz>
            <iyy>${m*(x*x+z*z)/12}</iyy>
            <iyz>0</iyz>
            <izz>${m*(x*x+z*z)/12}</izz>
        </inertia>
    </xacro_macro_define>
<!--use of macro-->
            <inertial>
                <pose>0 0 0.02 0 0 0</pose>
                <xacro_macro name="box_inertia" m="${mass}" x="0.3" y="0.1" z="0.2"/>
            </inertial>

generated xml

			<inertial>
				<pose>0 0 0.02 0 0 0</pose>
				<mass>0.2</mass>
				<inertia>
					<ixx>0.0008333333333333335</ixx>
					<ixy>0</ixy>
					<ixz>0</ixz>
					<iyy>0.002166666666666667</iyy>
					<iyz>0</iyz>
					<izz>0.002166666666666667</izz>
				</inertia>
			</inertial>

• only support simple parameters (string and number),but block parameters isn't supported.
• it's supported to use other xacro_macro in xacro_define_macro which is recursive definition.

it's not recommended to define macro recursively (only support <=5 ).

2.3. Math expressions

• within dollared-braces ${xxxx}, you can also write simple math expressions.
• refer to examples of Properties and Macros
• it's implemented by calling eval() in python, so it's unsafe for some cases.

2.4. Including other xacro files

definition include

You can include other xacro files using the <xacro_include_definition> tag ,include other xacro files according to param uri.

• it will only include the definition of properties with tag <xacro_define_property> and macros with tag <xacro_define_macro>.

<xacro_include_definition uri="model://simple_car/model.sdf.xacro"/>
<xacro_include_definition uri="file://simple_car/model.sdf.xacro"/>

• The uri for model means to search file in a list of folders which are defined by environment variable IGN_GAZEBO_RESOURCE_PATH and GAZEBO_MODEL_PATH
• The uri for file means to open the file directly. it try to open the file with relative path simple_car/model.sdf.xacro . you can also try to open file with absolute path /simple_car/model.sdf.xacro with uri file:///simple_car/model.sdf.xacro.

model include

You can include other xacro files using the <xacro_include_model> tag.

• it will only include the content between <model>...<model/> in other xacro file.

<xacro_include_model uri="model://simple_car/model.sdf.xacro"/>

Tips:

• <xacro_include_definition> supports to include recursively.
• <xacro_include_model> doesn't support to include recursively. and <xacro_include_definition> should be used before using <xacro_include_model> . * it's generally used to overwrite property with <xacro_define_property> .
• Don't use same name for xacro definition (the param name of <xacro_define_property> and <xacro_define_macro>) , otherwise the priority of xacro definition need be considered.
• Be carefully when using <xacro_include_definition> and <xacro_include_model>

2.5 pre-defined common.xacro

<!--macro defination:inertia-->
<xacro_define_macro name="inertia_cylinder" params="m r l">
<xacro_define_macro name="inertia_box" params="m x y z">
<xacro_define_macro name="inertia_sphere" params="m r">
<!--macro defination:geometry-->
<xacro_define_macro name="geometry_cylinder" params="r l">
<xacro_define_macro name="geometry_box" params="x y z">
<xacro_define_macro name="geometry_sphere" params="r">
<xacro_define_macro name="geometry_mesh" params="uri">
<!--macro defination:visual_collision_with_mesh-->
<xacro_define_macro name="visual_collision_with_mesh" params="prefix uri">

• you can directly use the macro in your xacro file.

3. Extra Explanation For Source Code

the Tag In model.sdf.xacro

• definition of property and macro： <xacro_define_property> and <xacro_define_macro>
  • the xacro defination (<xacro_define_property> and <xacro_define_macro>) must be child node of root node <sdf> .
• include : <xacro_include_definition> , <xacro_include_model>
• use of property and macro：${xxx} and <xacro_macro>

Steps of process (without include)

• use dictionary to store the definitions, property dictionary (<param,value>) and macro dictionary (<macro_name,xml_string>, <macro_name,params>) , and remove nodes with these tag.
• process global property ${xxx} between <model>...</model> by using eval()
• process tag <xacro_macro> , and replace <xacro_macro> with macro dictionary <macro_name,xml_string> according to the param name of <xacro_macro> , and use eval() to replace ${xxx} in <xacro_define_property> by using global property dictionary and local property dictionary.
  • the params of <xacro_define_property> make up global property dictionary , the params of <xacro_macro> make up local property dictionary.
  • it will recursively process 5 times.

4. Maintainer and License

maintainer : Ge Zhenpeng [e-mail]

xacro4sdf is provided under MIT.