Hello, thanks for any and all responses, but simply:
I am running a control loop that generates and publishes new velocities at 100hz, every-time it calculates a new velocity it needs the current motor shaft position data. However, this position data is subscribed To and arriving at a much higher rate than the control is running.
How can I/best method for accessing the current data from this subscribed to topic at the moment I need it in the control loop?
An example:
ros::Subscriber pointSub;
ros::Subscriber posSub;
float phi = 0.0; /// a global variable that gets updated
void controlLoop(const geometry_msgs::Point & currentPoint) {
//RUNS ONCE!!! triggered by arriving x,y,z point data
ros::Rate rate(100)
for(int i = 0 ; i < 100; i++)
{
//HERE I WANT THE UPDATED, most recent, PHI VALUE
ros::spinOnce();
rate.sleep();
}
} //END OF control loop
void fastPositionCb(const std_msgs::Float64 currPos) {
//Gets data published faster than 100hz .... say 1kHz
phi = CurrPos.data;
}
int main(int argc, char * argv[]) {
ros::init(argc, argv, "example");
ros::NodeHandle nh;
pointSub = nh.subscribe("testPoint", 1, controlLoop); // happens once
posSub = nh.subscribe("phiPos", 1, fastPositionCb); // happens very fast
// Spin
ros::spin();
}
Originally posted by PatFGarrett on ROS Answers with karma: 31 on 2020-01-30
Post score: 0
Original comments
Comment by Delb on 2020-01-30:
I'm not sure to fully understand what you want to achieve. Do you want to call the controlLoop callback faster than the fastPositionCb or only with the latest data received ?
Anyway I would change your code to have your callbacks only receiving the data and assigning it to some global variables (or better using classes) because looping in a callback is really not adivised, you should only do simple operations inside callbacks to ensure you receive all the messages. So the main would have a loop like this :
ros::Rate rate(YOUR_DESIRED_RATE)
while (ros::ok())
{
//Do what you need to with the data you received
ros::spinOnce();
rate.sleep();
}
Correct me if I misunderstood your issue I'll correct my suggestion accordingly.
Comment by PatFGarrett on 2020-01-30:
Delb,
Thanks for the response, and I apologize for not being very clear. But you are basically right... I want To harness the data coming in from a very fast topic and use it at a a rate of 100Hz. I adjusted my sample code To hopefully show this better
