[rosparam] do not overwrite an existing param or default value

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Hi all,

I'm looking for a way to specify a DEFAULT value for /some/parameter on the parameter server in a XML launch file. In other terms if it's already there I don't want to overwrite the previous value.

Also is it possible to test any other variable than a bool? I would like to do something like:

  <!-- THIS DOES NOT WORK -->
  <node if="$(arg method)==nearest" name="point_provider" pkg="point_providers" type="simple_publisher.py" />
  <node if="$(arg method)==regression" name="point_provider" pkg="regression_models" type="publisher.py" />

Is there any way to achieve this?

Also a complete control structure if/elif/else would be nice.

Thanks