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Yaml List to Parameter to Vector

asked 2017-05-18 16:45:27 -0500

conor.mcmahon gravatar image

updated 2017-05-18 17:00:29 -0500


I've been trying to store a list of doubles in a yaml file, load it into the parameter server, and later pull it back out from the server into a std::vector<double> in a cpp file, on ROS Kinetic.

yaml syntax I've used:

param_name:       [ .546, -.546, -.546,  .546,  .724, .724]

I've been able to get the list up into the parameter server without issue (currently, just via a 'rosparam load' terminal command on the yaml file). 'rosparam get' commands in the terminal return the expected values from it once it's there. However, when I try to retrieve the parameter within the cpp file I run into issues:

std::vector<double> param_list
if( !nh_.getParam("/param_name", param_list) )
    ROS_ERROR("Failed to get parameter from server.");

compiles, publishes the error message and fails to populate the vector. I've had confusing issues in the past dealing with ambiguous ros parameter server types so I've also tried this with a vector of floats with the same result. I think that the syntax I've used on the retrieval end matches that demonstrated here:

Do I have to do something to explicitly cast the data as the right type when I load it into the parameter server from the yaml?

I've also been able to get the XmlRpc method demonstrated in the above link to work with the vector - partly. I can retrieve the data and assert the list itself to be an array:

XmlRpc::XmlRpcValue param_list;
if( !nh_.getParam("/param_name", param_list) )
    ROS_ERROR("Still failed...");
ROS_ASSERT(param_list.getType() == XmlRpc::XmlRpcValue::TypeArray);

but when I try to assert the values in the array to be doubles:

for (int32_t i = 0; i < param_list.size(); ++i) 
  ROS_ASSERT(param_list[i].getType() == XmlRpc::XmlRpcValue::TypeDouble);

I get an "assertion failed" error on running the program. If I output the values in the array they seem correct even when not asserted to be doubles, but I get compile errors about "ambiguity" when I try to assign them to another, non-XmlRpc value later on. Either way though I'd really rather avoid using XmlRpc at all if I can make the vector stuff work instead!

In the past I've had similar setups work, pulling data out of a yaml file to the parameter server and then into a cpp file, but haven't ever been able to get yaml lists to cpp vectors to work.

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answered 2017-05-18 18:09:45 -0500

ufr3c_tjc gravatar image

Your retrieval methods look correct, meaning it's most likely a problem with the parameter itself. This may be inconsequential, but try putting a zero in front of your decimal values, rather than starting with the period. My code looks identical to yours, but I use zeros in the parameters.

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Wow, it looks like this did it, thanks!! Just made this change and it works as expected now.

conor.mcmahon gravatar image conor.mcmahon  ( 2017-05-18 18:13:26 -0500 )edit

Yeah sometimes it's the little things... Glad I could help!

ufr3c_tjc gravatar image ufr3c_tjc  ( 2017-05-18 18:17:03 -0500 )edit

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Asked: 2017-05-18 16:45:27 -0500

Seen: 9,727 times

Last updated: May 18 '17