rclcpp::Time epochs

Question

I would like to get seconds, and nanoseconds from inside my node, so I have a timer_callback that executes each 100ms, to note seconds and nanoseconds of the rclcpp::Time

    void timer_callback() {
        rclcpp::Time t = this->now();
        cout << unsigned(t.seconds()) << '\t' << unsigned(t.nanoseconds()) << endl;
    }

What I get is, number of seconds since last epoch, and a uint32 representation of nanoseconds, that is actually accurate, (1sec=1e9ns), in which is measurable by chaning timer1 frequency, i.e. a diff of the nanoseconds is usable, but it does not reset each second, basically it has its own 4.2~ second epoch.

What is the epoch for nanoseconds?

Any ideas on how to get the seconds and nanoseconds to make a timestamp that is microseconds accurate?

Best Regards, C.A.

[node-1] 1697373475 3482658792

[node-1] 1697373475 3982695401

[node-1] 1697373476 187537493

[node-1] 1697373476 687584889

[node-1] 1697373477 1187751915

[node-1] 1697373477 1687731420

[node-1] 1697373478 2187763841

[node-1] 1697373478 2687771385

[node-1] 1697373479 3187776990

[node-1] 1697373479 3687628969

Answer 1

I think the issue is in the unsigned() cast.

Code changed to this:

rclcpp::Time t = this->now();
std::cout << t.seconds() << '\t' << t.nanoseconds() << std::endl;
std::cout << unsigned(t.seconds()) << '\t' << unsigned(t.nanoseconds()) << std::endl;

Gives output:

1.6974e+09  1697398304675212161
1697398304  3498322817

Nanoseconds is not a uint32:

rclcpp::Time::nanoseconds() returns a rcl_time_point_value_t, which is a typedef of an rcutils_time_point_value_t, which is a typedef of an int64_t.