Perform calculation in .launch file

roslaunch

asked 2014-10-07 04:21:09 -0500

koenlek
432 ●10 ●16 ●23

Hi all,

I wondered if it is possible to do a calculation in a roslaunch file, something like:

<arg name="windowsize" default="20"/>

<node pkg="gmapping" type="slam_gmapping" name="slam_gmapping" output="screen" clear_params="true">
    <param name="xmin" value="$(arg -windowsize/2)" />
    <param name="ymin" value="$(arg  -windowsize/2)" />
    <param name="xmax" value="$(arg  windowsize/2)" />
    <param name="ymax" value="$(arg  windowsize/2)" />
</node>

I have tried several combinations, all without luck. And I can't seem to find anything about it on the web...

I really do need to be able to use the 'windowsize' argument, rather than 4 x/ymax/min arguments, to support some interface I made with other nodes I made...

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5

answered 2017-01-01 11:36:57 -0500

VictorLamoine

1495 ●35 ●57 ●69

This is possible starting from Kinetic thanks to the eval keyword:

For example:

<param name="circumference" value="$(eval 2.* 3.1415 * arg('radius'))"/>

http://wiki.ros.org/roslaunch/XML#sub...

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Comments

great! That's exactly what I was looking for.

koenlek ( 2017-01-02 04:48:06 -0500 )edit

Works on Melodic as well as Noetic. Tried and tested 👍🏻 ... It is the correct way to do math operations in launch file

pranshu ( 2023-04-15 09:51:15 -0500 )edit

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0

answered 2014-10-07 18:19:51 -0500

ct2034
862 ●21 ●75 ●44 https://twitter.com/ct2034

updated 2019-08-07 01:36:28 -0500

UPDATEThis changed in kinetic (see http://answers.ros.org/question/19436...)

As far as I am aware this wont be possible. The $(arg name)leads to substitution with the corresponding argument. But I think this only works for simple operations like replacements or logical decision lie if, unless. http://wiki.ros.org/roslaunch/XML