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ROSCPP - reading HZ from code

asked 2018-05-21 13:23:51 -0600

Gil404 gravatar image

Hi Guys,

trying to figure out a way to read a HZ data of a rostopic in my C++ code. I see that there is no API for it, so I am trying to execute the cmd by using popen and reading from the file. However since it is a constant stream it makes the process to halt. Any idea what is the right way to do it? I need only one "iteration" of the data.

this is my current method that works for other calls:

std::string MyClass::InvokeCmd(std::string command)
{
    std::string result;
    std::array<char, 128> buffer;
    FILE *pipe = popen(command.c_str(), "r");

        while (fgets(buffer.data(), 128, pipe) != NULL)
        {
            result += buffer.data();
        }
    }
    pclose(pipe);
    return result;
}
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read a HZ data of a rostopic

?

gvdhoorn gravatar imagegvdhoorn ( 2018-05-21 14:07:34 -0600 )edit

such as the avg rate, the min and the max....@gvdhoorn, do have any suggestion or tip?

Gil404 gravatar imageGil404 ( 2018-05-21 14:12:21 -0600 )edit

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answered 2018-05-21 13:52:51 -0600

It would be easier to subscribe to the topic from your own node and then record the time between callbacks. After two callbacks you could unsubscribe and the job's done.

It's best to avoid using command line tools from within programs, it's a very ugly solution.

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1

After two callbacks you could unsubscribe and the job's done.

Theoretically, this should be true. In reality though, you'll need a bit more events than two (to account for transient networking effects, OS scheduling, ROS event processing, etc).

gvdhoorn gravatar imagegvdhoorn ( 2018-05-21 14:07:06 -0600 )edit

I do understand that it is ugly, however, as also @gvdhoorn mentioned, 2 or 3 callbacks are not reliable enough.

Gil404 gravatar imageGil404 ( 2018-05-21 14:20:55 -0600 )edit

That's true, the longer you can sample the topic the more precise the frequency measurement will be.

PeteBlackerThe3rd gravatar imagePeteBlackerThe3rd ( 2018-05-21 17:04:26 -0600 )edit

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Asked: 2018-05-21 13:23:51 -0600

Seen: 398 times

Last updated: May 21 '18