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Remap inside a launch file vs remapping during rosbag play

asked 2020-07-25 04:30:42 -0600

praskot gravatar image

updated 2020-07-25 04:31:31 -0600

Hi All,

Goal (more of getting to know tutorial): Trying to run this particular code http://wiki.ros.org/image_pipeline/Tutorials/Simple%20image%20processor on an image from a rosbag.

Instead of changing the topic name inside the code (obviously this works), I tried the remap option in a launch file, which I thought is the better way. Tried the following two launch scripts,
launch_file1:

<launch>
  <node name="image_shrinker_node" pkg="image_shrinker" type="image_shrinker" output="screen">
  <remap from="/ns/camera1/image_raw" to="/camera/image_raw"/>
  </node>
</launch>

launch_file2:

<launch>
  <remap from="/ns/camera1/image_raw" to="/camera/image_raw"/>
  <node name="image_shrinker_node" pkg="image_shrinker" type="image_shrinker" output="screen">
  </node>
</launch>

Neither seems to work. The only I could get this to work is remapping it during rosbag play as, rosbag play bag_file.bag /ns/camera1/image_raw:=/camera/image_raw

Can anyone help me figure out what went wrong in the launch file?

Thank you

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1 Answer

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answered 2020-07-26 18:10:10 -0600

Geoff gravatar image

In both of your launch files, you are asking the image_shrinker node to remap its topic /ns/camera1/image_raw to /camera/image_raw. This is the wrong way around. from should specify the existing name, and to the name that you want to change it to. Because image_shrinker doesn't have a topic at /ns/camera1/image_raw the remapping rule has no effect.

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Thanks Geoff. That makes sense.

Also, does that mean remap works only on the publisher's end?

praskot gravatar image praskot  ( 2020-07-26 20:21:28 -0600 )edit

No, remapping works just fine on the subscriber as well.

Geoff gravatar image Geoff  ( 2020-07-26 20:31:27 -0600 )edit

I see! Thanks

This works,

<launch>
  <node name="image_shrinker_node" pkg="image_shrinker" type="image_shrinker" output="screen">
  <remap from="/camera/image_raw" to="/ns/camera1/image_raw"/>
  </node>
</launch>
praskot gravatar image praskot  ( 2020-07-26 22:26:02 -0600 )edit

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Asked: 2020-07-25 04:30:42 -0600

Seen: 142 times

Last updated: Jul 26 '20