Getting hierarchy level of yaml parameter

Question

Hi,

I want to use ros param to traverse files like this:

pcl_filter:
  filter:
    filter_cascade_1: 
      in:  cloud_in
      out: cloud_out
      filter:
        first_applied_filter:
          - config_for_filter_1
          - config_for_filter_2
        second_applied_filter:
          - config_for_filter_1
          - config_for_filter_2
    filter_cascade_2:
      in:  other_cloud_in
      out: other_cloud_out
      filter:
        first_applied_filter:
          - config_for_filter_1
          - config_for_filter_2
        second_applied_filter:
          - config_for_filter_1
          - config_for_filter_2

There I would like to get all cascades of the param "filter". In the node pcl_filter I search for something like

std::vector<std::string> param;
getParam("filter", param);

But this just seems to work with something like:

pcl_filter:
  filter:
    - filter_cascade_1
    - filter_cascade_1

And:

std::map<std::string, std::string> param;
getParam("filter", param);

just workes with:

pcl_filter:
  filter:
    filter_cascade_1: a
    filter_cascade_1: b

Does somebody know a way to get all of these parameter?

Thanks for your help

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Originally posted by Tobias Neumann on ROS Answers with karma: 179 on 2014-08-07

Post score: 3

Answer 1

I just did this for one of my packages. Here is some example code:

#include <XmlRpcValue.h>
...

void my_node::parseParams(ros::NodeHandle n) {
  XmlRpc::XmlRpcValue filters;
  n.getParam("filter", filters);
  ROS_ASSERT(filters.getType() == XmlRpc::XmlRpcValue::TypeStruct);
  for(XmlRpc::XmlRpcValue::ValueStruct::const_iterator it = filters.begin(); it != filters.end(); ++it) {
    ROS_INFO_STREAM("Found filter: " << (std::string)(it->first) << " ==> " << filters[it->first]);
    // Do stuff with filters:
    ROS_INFO_STREAM("filter_cascade_1: in: " << filters[it->first]["in"]);
    ROS_INFO_STREAM("filter_cascade_1: filter: first_applied_filter: config_for_filter_1: " << filters[it->first]["filter"]["first_applied_filter"][0]);
  }
}

This works with xmlrpc structs which is what you get when you query arbitrary parameter namespaces. The iterator contains as it->first the keys of all the parameters found in the filter namespace: filter_cascade_1 and filter_cascade_2 and the it->second contains a xmlrpc struct of the parameters in that namespace. It is not really nice or convenient to use but I hope the example helps a bit.

Edit: Just to elaborate a bit more, the XmlRpcValue::TypeStruct is just a std::map<std::string,XmlRpcValue::TypeStruct>. If you look at the output of this line ROS_INFO_STREAM("Found filter: " << (std::string)(it->first) << " ==> " << filters[it->first]); it should be quite clear how to use it I hope. Took me a few hours to find the right way of doing this so if you have any problems, just let me know.

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Originally posted by Chrissi with karma: 1642 on 2014-08-07

This answer was ACCEPTED on the original site

Post score: 8

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Original comments

Comment by Tobias Neumann on 2014-08-07:
Thank you very much, this is what I needed :) Unfortunately there is no ´std::mapstd::string,XmlRpcValue::TypeStruct´, that would produce much better code to read, but your solution works just as intended

Comment by Chrissi on 2014-08-07:
You're welcome. I know it's a bit messy... The python interface for this is much better I have to admit but sometimes you just can't avoid using some C++ as well :(