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Question
Is there any possibility to call a service from a launch.py file in ROS2?
Details
I have written a python node with a service which is launched by a launch.py file. Within the same launch file I would like to call the service of this node multiple times (with different argument values). Is there any possibility to realize this in ROS2?
This one is pretty straight forward, but took me a non-trivial amount of searching to find for myself. I posted this answer somewhere else recently, but since this question is the top search result, I thought I'd copy it here as well.
from launch.substitutions import FindExecutable
from launch.actions import ExecuteProcess
...
ld.add_action(
ExecuteProcess(
cmd=[[
FindExecutable(name='ros2'),
" service call ",
"/namespace/service_to_call ",
"example_msgs/srv/ExampleMsg ",
'"{param_1: True, param_2: 0.0}"',
]],
shell=True
)
)
Note the following:
ld here is a variable containing an instance of LaunchDescription/namespace/service_to_call is replaced with the service you're looking to call (don't forget any appropriate namespaces) and can be found with ros2 service listexample_msgs/srv/ExampleMsg is the message type used by that service, which you can get with ros2 service info /namespace/service_to_call"{param_1: True, param_2: 0.0}" is the dictionary defining the message data. To find the parameters you need to set, you may need to consult the .srv file or documentation.Don't forget to include the shell=True argument, as the command will fail with a confusing "File not found" error without it.
Thanks @luckierdodge! Just add more methods. Both examples below start a sim window and add another turtle2.
Method 1
Based on @luckierdodge answer:
from launch import LaunchDescription
from launch.actions import ExecuteProcess
from launch.substitutions import FindExecutable
from launch_ros.actions import Node
def generate_launch_description():
ld = LaunchDescription(
[
Node(
package="turtlesim",
executable="turtlesim_node",
name="turtlesim",
),
]
)
ld.add_action(
ExecuteProcess(
cmd=[
[
FindExecutable(name="ros2"),
" service call ",
"/spawn ",
"turtlesim/srv/Spawn ",
"\"{x: 2.0, y: 2.0, theta: 0.0, name: 'turtle2'}\"",
]
],
shell=True,
)
)
return ld
Method 2
Based on https://docs.ros.org/en/humble/Tutori...
from launch import LaunchDescription
from launch.actions import ExecuteProcess, LogInfo, RegisterEventHandler
from launch.event_handlers import OnProcessStart
from launch.substitutions import FindExecutable, LaunchConfiguration
from launch_ros.actions import Node
def generate_launch_description():
turtlesim_node = Node(
package="turtlesim",
executable="turtlesim_node",
name="sim",
)
spawn_turtle = ExecuteProcess(
cmd=[
[
FindExecutable(name="ros2"),
" service call ",
"/spawn ",
"turtlesim/srv/Spawn ",
"\"{x: 2.0, y: 2.0, theta: 0.0, name: 'turtle2'}\"",
]
],
shell=True,
)
return LaunchDescription(
[
turtlesim_node,
RegisterEventHandler(
OnProcessStart(
target_action=turtlesim_node,
on_start=[
LogInfo(msg="Turtlesim started, spawning turtle"),
spawn_turtle,
],
)
),
]
)
Asked: 2021-08-18 02:49:44 -0500
Seen: 2,092 times
Last updated: Jan 03 '23
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