WEBOTS - Write controller data to external CSV file

Question

I have this code from webots lidar.wbt . I need to get some lidar data to be plotted using opengl for another project.

#include <webots/distance_sensor.h>
#include <webots/lidar.h>
#include <webots/motor.h>
#include <webots/robot.h>

#include <stdio.h>

#define TIME_STEP 32
#define LEFT 0
#define RIGHT 1

using namespace std;

int main(int argc, char **argv) {
  // iterator used to parse loops
  int i, k;

  // init Webots stuff
  wb_robot_init();

  // init camera
  WbDeviceTag lidar = wb_robot_get_device("lidar");
  wb_lidar_enable(lidar, TIME_STEP);
  wb_lidar_enable_point_cloud(lidar);

  // init distance sensors
  WbDeviceTag us[2];
  double us_values[2];
  us[LEFT] = wb_robot_get_device("us0");
  us[RIGHT] = wb_robot_get_device("us1");
  for (i = 0; i < 2; ++i)
    wb_distance_sensor_enable(us[i], TIME_STEP);

  // get a handler to the motors and set target position to infinity (speed control).
  WbDeviceTag left_motor = wb_robot_get_device("left wheel motor");
  WbDeviceTag right_motor = wb_robot_get_device("right wheel motor");
  wb_motor_set_position(left_motor, INFINITY);
  wb_motor_set_position(right_motor, INFINITY);
  wb_motor_set_velocity(left_motor, 0.0);
  wb_motor_set_velocity(right_motor, 0.0);

  // set empirical coefficients for collision avoidance
  double coefficients[2][2] = {{12.0, -6.0}, {-10.0, 8.0}};
  double base_speed = 6.0;



  // init speed values
  double speed[2];

  while (wb_robot_step(TIME_STEP) != -1) {
    // read sensors
    for (i = 0; i < 2; ++i)
      us_values[i] = wb_distance_sensor_get_value(us[i]);

    // compute speed
    for (i = 0; i < 2; ++i) {
      speed[i] = 0.0;
      for (k = 0; k < 2; ++k)
        speed[i] += us_values[k] * coefficients[i][k];
    }

    // set actuators
    wb_motor_set_velocity(left_motor, base_speed + speed[LEFT]);
    wb_motor_set_velocity(right_motor, base_speed + speed[RIGHT]);
  }

  wb_robot_cleanup();

  return 0;
}

The data is supposed to be stored in us_values[i] . Hence, I need the the data inside array us_values[i] to a csv file.

I have tried cout and printf but is not giving any output. Please provide a solution. Thanks

Where do you attempt to print the values of us_values? Please show us your actual attempt. — Some programmer dude
– Some programmer dude, Commented Dec 10, 2019 at 9:10
I attempted using printf("Data %f\n", us_values[i]); below us_values[i] = wb_distance_sensor_get_value(us[i]); but the console was not showing anything — Sid133
– Sid133, Commented Dec 10, 2019 at 9:36
Please edit your question to update the minimal reproducible example. — Some programmer dude
– Some programmer dude, Commented Dec 10, 2019 at 9:37
A better question would have been: how to create a CSV file in C. I'm sure there are a lot of resources about this. — FabienRohrer
– FabienRohrer, Commented Dec 12, 2019 at 7:50

Sasha Gervais-Tourangeau · Accepted Answer · 2019-12-10 12:47:34Z

There is no printf or std::cout in the code you provided. If you're just looking for a way to create CSV files then here's a sample for how I create CSV files using std::fstream, it's fairly similar to how you'd use std::cout except there's a little bit of extra overhead.

#include <fstream>

int main(int argc, char* argv[]) {
    //generate values to be stored in CSV
    constexpr size_t arraySize(100);
    double values[arraySize];
    for(int i = 0; i < arraySize; i++) {
        values[i] = 1.0 / (i + 1);
    }

    //actually store those values...
    std::fstream file;
    file.open("Output.csv", std::fstream::out);
    for(int i = 0; i < arraySize; i++) {
        file << values[i] << ", ";
    }
    file.close();

    return 0;
}

If you want to print to stdout for piping then std::cout would be best. If you want to print directly to a file then you can use std::fstream.

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