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将启动文件从 ROS 1 迁移到 ROS 2

本指南介绍了如何编写 XML 启动文件，以便轻松地从 ROS 1.X 迁移。

背景

关于 ROS 2 launch 系统及其 Python API 的描述可以在 launch 系统教程 中找到。

将标签从 ROS 1 迁移到 ROS 2

launch

node

  • 在 ROS 1 中可用。

  • 启动一个新的节点。

  • 与 ROS 1 的区别：

    • type 属性现在是 exec。

    • ns 属性现在是 namespace。

    • 以下属性不可用：machine、respawn、respawn_delay、clear_params。

示例

<launch>
   <node pkg="demo_nodes_cpp" exec="talker"/>
   <node pkg="demo_nodes_cpp" exec="listener"/>
</launch>

param

  • ROS 1 可得到。

  • 用于向一个节点传递参数。

  • 在 ROS 2 中没有全局参数的概念。由于这个原因，它只能嵌套在 node 标签中使用。有些属性在 ROS 2 中不被支持：type、textfile、binfile、executable、command。

示例

<launch>
   <node pkg="demo_nodes_cpp" exec="parameter_event">
      <param name="foo" value="5"/>
   </node>
</launch>

类型推论规则

这里有一些如何写参数的例子：

<node pkg="my_package" exec="my_executable" name="my_node">
   <!--A string parameter with value "1"-->
   <param name="a_string" value="'1'"/>
   <!--A integer parameter with value 1-->
   <param name="an_int" value="1"/>
   <!--A float parameter with value 1.0-->
   <param name="a_float" value="1.0"/>
   <!--A string parameter with value "asd"-->
   <param name="another_string" value="asd"/>
   <!--Another string parameter, with value "asd"-->
   <param name="string_with_same_value_as_above" value="'asd'"/>
   <!--Another string parameter, with value "'asd'"-->
   <param name="quoted_string" value="\'asd\'"/>
   <!--A list of strings, with value ["asd", "bsd", "csd"]-->
   <param name="list_of_strings" value="asd, bsd, csd" value-sep=", "/>
   <!--A list of ints, with value [1, 2, 3]-->
   <param name="list_of_ints" value="1,2,3" value-sep=","/>
   <!--Another list of strings, with value ["1", "2", "3"]-->
   <param name="another_list_of_strings" value="'1';'2';'3'" value-sep=";"/>
   <!--A list of strings using an strange separator, with value ["1", "2", "3"]-->
   <param name="strange_separator" value="'1'//'2'//'3'" value-sep="//"/>
</node>

Parameter grouping

In ROS 2, param tags are allowed to be nested. For example:

<node pkg="my_package" exec="my_executable" name="my_node" ns="/an_absoulute_ns">
   <param name="group1">
      <param name="group2">
         <param name="my_param" value="1"/>
      </param>
      <param name="another_param" value="2"/>
   </param>
</node>

That will create two parameters:

  • A group1.group2.my_param of value 1, hosted by node /an_absolute_ns/my_node.

  • A group1.another_param of value 2 hosted by node /an_absolute_ns/my_node.

It’s also possible to use full parameter names:

<node pkg="my_package" exec="my_executable" name="my_node" ns="/an_absoulute_ns">
   <param name="group1.group2.my_param" value="1"/>
   <param name="group1.another_param" value="2"/>
</node>

rosparam

  • Available in ROS 1.

  • Loads parameters from a yaml file.

  • It has been replaced with a from attribute in param tags.

示例

<node pkg="my_package" exec="my_executable" name="my_node" ns="/an_absoulute_ns">
   <param from="/path/to/file"/>
</node>

remap

  • Available in ROS 1.

  • Used to pass remapping rules to a node.

  • It can only be used within node tags.

示例

<launch>
   <node pkg="demo_nodes_cpp" exec="talker">
      <remap from="chatter" to="my_topic"/>
   </node>
   <node pkg="demo_nodes_cpp" exec="listener">
      <remap from="chatter" to="my_topic"/>
   </node>
</launch>

include

  • Available in ROS 1.

  • Allows including another launch file.

  • 与 ROS 1 的区别：

    • Available in ROS 1, included content was scoped. In ROS 2, it’s not. Nest includes in group tags to scope them.

    • ns attribute is not supported. See example of push-ros-namespace tag for a workaround.

    • arg tags nested in an include tag don’t support conditionals (if or unless).

    • There is no support for nested env tags. set_env and unset_env can be used instead.

    • Both clear_params and pass_all_args attributes aren’t supported.

arg

  • Available in ROS 1.

  • arg is used for declaring a launch argument, or to pass an argument when using include tags.

  • 与 ROS 1 的区别：

    • value attribute is not allowed. Use let tag for this.

    • doc is now description.

    • When nested within an include tag, if and unless attributes aren’t allowed.

示例

<launch>
   <arg name="topic_name" default="chatter"/>
   <node pkg="demo_nodes_cpp" exec="talker">
      <remap from="chatter" to="$(var topic_name)"/>
   </node>
   <node pkg="demo_nodes_cpp" exec="listener">
      <remap from="chatter" to="$(var topic_name)"/>
   </node>
</launch>

Passing an argument via the command line

See ROS 2 launch tutorial.

env

  • Available in ROS 1.

  • Sets an environment variable.

  • It has been replaced with env, set_env and unset_env:

    • env can only be used nested in a node or executable tag. if and unless tags aren’t supported.

    • set_env can be nested within the root tag launch or in group tags. It accepts the same attributes as env, and also if and unless tags.

    • unset_env unsets an environment variable. It accepts a name attribute and conditionals.

示例

<launch>
   <set_env name="MY_ENV_VAR" value="MY_VALUE" if="CONDITION_A"/>
   <set_env name="ANOTHER_ENV_VAR" value="ANOTHER_VALUE" unless="CONDITION_B"/>
   <set_env name="SOME_ENV_VAR" value="SOME_VALUE"/>
   <node pkg="MY_PACKAGE" exec="MY_EXECUTABLE" name="MY_NODE">
      <env name="NODE_ENV_VAR" value="SOME_VALUE"/>
   </node>
   <unset_env name="MY_ENV_VAR" if="CONDITION_A"/>
   <node pkg="ANOTHER_PACKAGE" exec="ANOTHER_EXECUTABLE" name="ANOTHER_NODE"/>
   <unset_env name="ANOTHER_ENV_VAR" unless="CONDITION_B"/>
   <unset_env name="SOME_ENV_VAR"/>
</launch>

group

  • Available in ROS 1.

  • Allows limiting the scope of launch configurations. Usually used together with let, include and push-ros-namespace tags.

  • 与 ROS 1 的区别：

    • There is no ns attribute. See the new push-ros-namespace tag as a workaround.

    • clear_params attribute isn’t available.

    • It doesn’t accept remap nor param tags as children.

示例

launch-prefix configuration affects both executable and node tags’ actions. This example will use time as a prefix if use_time_prefix_in_talker argument is 1, only for the talker.

<launch>
   <arg name="use_time_prefix_in_talker" default="0"/>
   <group>
      <let name="launch-prefix" value="time" if="$(var use_time_prefix_in_talker)"/>
      <node pkg="demo_nodes_cpp" exec="talker"/>
   </group>
   <node pkg="demo_nodes_cpp" exec="listener"/>
</launch>

machine

It is not supported at the moment.

test

It is not supported at the moment.

New tags in ROS 2

set_env and unset_env

See env tag decription.

push-ros-namespace

include and group tags don’t accept an ns attribute. This action can be used as a workaround:

<!-Other tags-->
<group>
   <push-ros-namespace namespace="my_ns"/>
   <!--Nodes here are namespaced with "my_ns".-->
   <!--If there is an include action here, its nodes will also be namespaced.-->
   <push-ros-namespace namespace="another_ns"/>
   <!--Nodes here are namespaced with "another_ns/my_ns".-->
   <push-ros-namespace namespace="/absolute_ns"/>
   <!--Nodes here are namespaced with "/absolute_ns".-->
   <!--The following node receives an absolute namespace, so it will ignore the others previously pushed.-->
   <!--The full path of the node will be /asd/my_node.-->
   <node pkg="my_pkg" exec="my_executable" name="my_node" ns="/asd"/>
</group>
<!--Nodes outside the group action won't be namespaced.-->
<!-Other tags-->

let

It’s a replacement of arg tag with a value attribute.

<let var="foo" value="asd"/>

executable

It allows running any executable.

示例

<executable cmd="ls -las" cwd="/var/log" name="my_exec" launch-prefix="something" output="screen" shell="true">
   <env name="LD_LIBRARY" value="/lib/some.so"/>
</executable>

Replacing an include tag

To have exactly the same behavior as Available in ROS 1, include tags must be nested in a group tag.

<group>
   <include file="another_launch_file"/>
</group>

To replace the ns attribute, push-ros-namespace action must be used:

<group>
   <push-ros-namespace namespace="my_ns"/>
   <include file="another_launch_file"/>
</group>

Substitutions

Documentation about ROS 1’s substitutions can be found in roslaunch XML wiki. Substitutions syntax hasn’t changed, i.e. it still follows the $(substitution-name arg1 arg2 ...) pattern. There are, however, some changes w.r.t. ROS 1:

  • env and optenv tags have been replaced by the env tag. $(env <NAME>) will fail if the environment variable doesn’t exist. $(env <NAME> '') does the same as ROS 1’s $(optenv <NAME>). $(env <NAME> <DEFAULT>) does the same as ROS 1’s $(env <NAME> <DEFAULT>) or $(optenv <NAME> <DEFAULT>).

  • find has been replaced with find-pkg-share (substituting the share directory of an installed package). Alternatively find-pkg-prefix will return the root of an installed package.

  • There is a new exec-in-pkg substitution. e.g.: $(exec-in-pkg <package_name> <exec_name>).

  • There is a new find-exec substitution.

  • arg has been replaced with var. It looks at configurations defined either with arg or let tag.

  • eval and dirname substitutions haven’t changed.

  • anon substitution is not supported.

类型推论规则

The rules that were shown in Type inference rules subsection of param tag applies to any attribute. For example:

<!--Setting a string value to an attribute expecting an int will raise an error.-->
<tag1 attr-expecting-an-int="'1'"/>
<!--Correct version.-->
<tag1 attr-expecting-an-int="1"/>
<!--Setting an integer in an attribute expecting a string will raise an error.-->
<tag2 attr-expecting-a-str="1"/>
<!--Correct version.-->
<tag2 attr-expecting-a-str="'1'"/>
<!--Setting a list of strings in an attribute expecting a string will raise an error.-->
<tag3 attr-expecting-a-str="asd, bsd" str-attr-sep=", "/>
<!--Correct version.-->
<tag3 attr-expecting-a-str="don't use a separator"/>

Some attributes accept more than a single type, for example value attribute of param tag. It’s usual that parameters that are of type int (or float) also accept an str, that will be later substituted and tried to convert to an int (or float) by the action.