iterative_time_parameterization.cpp

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/* Author: Ken Anderson */
 
#include <moveit/trajectory_processing/iterative_time_parameterization.h>
#include <moveit_msgs/JointLimits.h>
#include <moveit/robot_state/conversions.h>
 
namespace trajectory_processing
{
static const double DEFAULT_VEL_MAX = 1.0;
static const double DEFAULT_ACCEL_MAX = 1.0;
static const double ROUNDING_THRESHOLD = 0.01;
 
IterativeParabolicTimeParameterization::IterativeParabolicTimeParameterization(unsigned int max_iterations,
                                                                               double max_time_change_per_it)
  : max_iterations_(max_iterations), max_time_change_per_it_(max_time_change_per_it)
{
}
 
#if 0  // unused functions
namespace
{
void printPoint(const trajectory_msgs::JointTrajectoryPoint& point, std::size_t i)
{
  ROS_DEBUG_NAMED("trajectory_processing.iterative_time_parameterization", " time   [%zu]= %f", i,
                  point.time_from_start.toSec());
  if (point.positions.size() >= 7)
  {
    ROS_DEBUG_NAMED("trajectory_processing.iterative_time_parameterization", " pos_   [%zu]= %f %f %f %f %f %f %f", i,
                    point.positions[0], point.positions[1], point.positions[2], point.positions[3], point.positions[4],
                    point.positions[5], point.positions[6]);
  }
  if (point.velocities.size() >= 7)
  {
    ROS_DEBUG_NAMED("trajectory_processing.iterative_time_parameterization", "  vel_  [%zu]= %f %f %f %f %f %f %f", i,
                    point.velocities[0], point.velocities[1], point.velocities[2], point.velocities[3],
                    point.velocities[4], point.velocities[5], point.velocities[6]);
  }
  if (point.accelerations.size() >= 7)
  {
    ROS_DEBUG_NAMED("trajectory_processing.iterative_time_parameterization", "   acc_ [%zu]= %f %f %f %f %f %f %f", i,
                    point.accelerations[0], point.accelerations[1], point.accelerations[2], point.accelerations[3],
                    point.accelerations[4], point.accelerations[5], point.accelerations[6]);
  }
}
 
void printStats(const trajectory_msgs::JointTrajectory& trajectory, const std::vector<moveit_msgs::JointLimits>& limits)
{
  ROS_DEBUG_NAMED("trajectory_processing.iterative_time_parameterization", "jointNames= %s %s %s %s %s %s %s",
                  limits[0].joint_name.c_str(), limits[1].joint_name.c_str(), limits[2].joint_name.c_str(),
                  limits[3].joint_name.c_str(), limits[4].joint_name.c_str(), limits[5].joint_name.c_str(),
                  limits[6].joint_name.c_str());
  ROS_DEBUG_NAMED("trajectory_processing.iterative_time_parameterization", "maxVelocities= %f %f %f %f %f %f %f",
                  limits[0].max_velocity, limits[1].max_velocity, limits[2].max_velocity, limits[3].max_velocity,
                  limits[4].max_velocity, limits[5].max_velocity, limits[6].max_velocity);
  ROS_DEBUG_NAMED("trajectory_processing.iterative_time_parameterization", "maxAccelerations= %f %f %f %f %f %f %f",
                  limits[0].max_acceleration, limits[1].max_acceleration, limits[2].max_acceleration,
                  limits[3].max_acceleration, limits[4].max_acceleration, limits[5].max_acceleration,
                  limits[6].max_acceleration);
  // for every point in time:
  for (std::size_t i = 0; i < trajectory.points.size(); ++i)
    printPoint(trajectory.points[i], i);
}
}  // namespace
#endif
 
// Applies velocity
void IterativeParabolicTimeParameterization::applyVelocityConstraints(robot_trajectory::RobotTrajectory& rob_trajectory,
                                                                      std::vector<double>& time_diff,
                                                                      const double max_velocity_scaling_factor) const
{
  const moveit::core::JointModelGroup* group = rob_trajectory.getGroup();
  const std::vector<std::string>& vars = group->getVariableNames();
  const std::vector<int>& idx = group->getVariableIndexList();
  const moveit::core::RobotModel& rmodel = group->getParentModel();
  const int num_points = rob_trajectory.getWayPointCount();
 
  double velocity_scaling_factor = 1.0;
 
  if (max_velocity_scaling_factor > 0.0 && max_velocity_scaling_factor <= 1.0)
    velocity_scaling_factor = max_velocity_scaling_factor;
  else if (max_velocity_scaling_factor == 0.0)
    ROS_DEBUG_NAMED("trajectory_processing.iterative_time_parameterization",
                    "A max_velocity_scaling_factor of 0.0 was specified, defaulting to %f instead.",
                    velocity_scaling_factor);
  else
    ROS_WARN_NAMED("trajectory_processing.iterative_time_parameterization",
                   "Invalid max_velocity_scaling_factor %f specified, defaulting to %f instead.",
                   max_velocity_scaling_factor, velocity_scaling_factor);
 
  for (int i = 0; i < num_points - 1; ++i)
  {
    const moveit::core::RobotStatePtr& curr_waypoint = rob_trajectory.getWayPointPtr(i);
    const moveit::core::RobotStatePtr& next_waypoint = rob_trajectory.getWayPointPtr(i + 1);
 
    for (std::size_t j = 0; j < vars.size(); ++j)
    {
      double v_max = DEFAULT_VEL_MAX;
      const moveit::core::VariableBounds& b = rmodel.getVariableBounds(vars[j]);
      if (b.velocity_bounded_)
        v_max =
            std::min(fabs(b.max_velocity_ * velocity_scaling_factor), fabs(b.min_velocity_ * velocity_scaling_factor));
      const double dq1 = curr_waypoint->getVariablePosition(idx[j]);
      const double dq2 = next_waypoint->getVariablePosition(idx[j]);
      const double t_min = std::abs(dq2 - dq1) / v_max;
      if (t_min > time_diff[i])
        time_diff[i] = t_min;
    }
  }
}
 
// Iteratively expand dt1 interval by a constant factor until within acceleration constraint
// In the future we may want to solve to quadratic equation to get the exact timing interval.
// To do this, use the CubicTrajectory::quadSolve() function in cubic_trajectory.h
double IterativeParabolicTimeParameterization::findT1(const double dq1, const double dq2, double dt1, const double dt2,
                                                      const double a_max) const
{
  const double mult_factor = 1.01;
  double v1 = (dq1) / dt1;
  double v2 = (dq2) / dt2;
  double a = 2.0 * (v2 - v1) / (dt1 + dt2);
 
  while (std::abs(a) > a_max)
  {
    v1 = (dq1) / dt1;
    v2 = (dq2) / dt2;
    a = 2.0 * (v2 - v1) / (dt1 + dt2);
    dt1 *= mult_factor;
  }
 
  return dt1;
}
 
double IterativeParabolicTimeParameterization::findT2(const double dq1, const double dq2, const double dt1, double dt2,
                                                      const double a_max) const
{
  const double mult_factor = 1.01;
  double v1 = (dq1) / dt1;
  double v2 = (dq2) / dt2;
  double a = 2.0 * (v2 - v1) / (dt1 + dt2);
 
  while (std::abs(a) > a_max)
  {
    v1 = (dq1) / dt1;
    v2 = (dq2) / dt2;
    a = 2.0 * (v2 - v1) / (dt1 + dt2);
    dt2 *= mult_factor;
  }
 
  return dt2;
}
 
// Takes the time differences, and updates the timestamps, velocities and accelerations
// in the trajectory.
void IterativeParabolicTimeParameterization::updateTrajectory(robot_trajectory::RobotTrajectory& rob_trajectory,
                                                              const std::vector<double>& time_diff)
{
  // Error check
  if (time_diff.empty())
    return;
 
  double time_sum = 0.0;
 
  moveit::core::RobotStatePtr prev_waypoint;
  moveit::core::RobotStatePtr curr_waypoint;
  moveit::core::RobotStatePtr next_waypoint;
 
  const moveit::core::JointModelGroup* group = rob_trajectory.getGroup();
  const std::vector<std::string>& vars = group->getVariableNames();
  const std::vector<int>& idx = group->getVariableIndexList();
 
  int num_points = rob_trajectory.getWayPointCount();
 
  rob_trajectory.setWayPointDurationFromPrevious(0, time_sum);
 
  // Times
  for (int i = 1; i < num_points; ++i)
    // Update the time between the waypoints in the robot_trajectory.
    rob_trajectory.setWayPointDurationFromPrevious(i, time_diff[i - 1]);
 
  // Return if there is only one point in the trajectory!
  if (num_points <= 1)
    return;
 
  // Accelerations
  for (int i = 0; i < num_points; ++i)
  {
    curr_waypoint = rob_trajectory.getWayPointPtr(i);
 
    if (i > 0)
      prev_waypoint = rob_trajectory.getWayPointPtr(i - 1);
 
    if (i < num_points - 1)
      next_waypoint = rob_trajectory.getWayPointPtr(i + 1);
 
    for (std::size_t j = 0; j < vars.size(); ++j)
    {
      double q1;
      double q2;
      double q3;
      double dt1;
      double dt2;
 
      if (i == 0)
      {
        // First point
        q1 = next_waypoint->getVariablePosition(idx[j]);
        q2 = curr_waypoint->getVariablePosition(idx[j]);
        q3 = q1;
 
        dt1 = dt2 = time_diff[i];
      }
      else if (i < num_points - 1)
      {
        // middle points
        q1 = prev_waypoint->getVariablePosition(idx[j]);
        q2 = curr_waypoint->getVariablePosition(idx[j]);
        q3 = next_waypoint->getVariablePosition(idx[j]);
 
        dt1 = time_diff[i - 1];
        dt2 = time_diff[i];
      }
      else
      {
        // last point
        q1 = prev_waypoint->getVariablePosition(idx[j]);
        q2 = curr_waypoint->getVariablePosition(idx[j]);
        q3 = q1;
 
        dt1 = dt2 = time_diff[i - 1];
      }
 
      double v1, v2, a;
 
      bool start_velocity = false;
      if (dt1 == 0.0 || dt2 == 0.0)
      {
        v1 = 0.0;
        v2 = 0.0;
        a = 0.0;
      }
      else
      {
        if (i == 0)
        {
          if (curr_waypoint->hasVelocities())
          {
            start_velocity = true;
            v1 = curr_waypoint->getVariableVelocity(idx[j]);
          }
        }
        v1 = start_velocity ? v1 : (q2 - q1) / dt1;
        // v2 = (q3-q2)/dt2;
        v2 = start_velocity ? v1 : (q3 - q2) / dt2;  // Needed to ensure continuous velocity for first point
        a = 2.0 * (v2 - v1) / (dt1 + dt2);
      }
 
      curr_waypoint->setVariableVelocity(idx[j], (v2 + v1) / 2.0);
      curr_waypoint->setVariableAcceleration(idx[j], a);
    }
  }
}
 
// Applies Acceleration constraints
void IterativeParabolicTimeParameterization::applyAccelerationConstraints(
    robot_trajectory::RobotTrajectory& rob_trajectory, std::vector<double>& time_diff,
    const double max_acceleration_scaling_factor) const
{
  moveit::core::RobotStatePtr prev_waypoint;
  moveit::core::RobotStatePtr curr_waypoint;
  moveit::core::RobotStatePtr next_waypoint;
 
  const moveit::core::JointModelGroup* group = rob_trajectory.getGroup();
  const std::vector<std::string>& vars = group->getVariableNames();
  const std::vector<int>& idx = group->getVariableIndexList();
  const moveit::core::RobotModel& rmodel = group->getParentModel();
 
  const int num_points = rob_trajectory.getWayPointCount();
  const unsigned int num_joints = group->getVariableCount();
  int num_updates = 0;
  int iteration = 0;
  bool backwards = false;
  double q1;
  double q2;
  double q3;
  double dt1;
  double dt2;
  double v1;
  double v2;
  double a;
 
  double acceleration_scaling_factor = 1.0;
 
  if (max_acceleration_scaling_factor > 0.0 && max_acceleration_scaling_factor <= 1.0)
    acceleration_scaling_factor = max_acceleration_scaling_factor;
  else if (max_acceleration_scaling_factor == 0.0)
    ROS_DEBUG_NAMED("trajectory_processing.iterative_time_parameterization",
                    "A max_acceleration_scaling_factor of 0.0 was specified, defaulting to %f instead.",
                    acceleration_scaling_factor);
  else
    ROS_WARN_NAMED("trajectory_processing.iterative_time_parameterization",
                   "Invalid max_acceleration_scaling_factor %f specified, defaulting to %f instead.",
                   max_acceleration_scaling_factor, acceleration_scaling_factor);
 
  do
  {
    num_updates = 0;
    iteration++;
 
    // In this case we iterate through the joints on the outer loop.
    // This is so that any time interval increases have a chance to get propogated through the trajectory
    for (unsigned int j = 0; j < num_joints; ++j)
    {
      // Loop forwards, then backwards
      for (int count = 0; count < 2; ++count)
      {
        for (int i = 0; i < num_points - 1; ++i)
        {
          int index = backwards ? (num_points - 1) - i : i;
 
          curr_waypoint = rob_trajectory.getWayPointPtr(index);
 
          if (index > 0)
            prev_waypoint = rob_trajectory.getWayPointPtr(index - 1);
 
          if (index < num_points - 1)
            next_waypoint = rob_trajectory.getWayPointPtr(index + 1);
 
          // Get acceleration limits
          double a_max = DEFAULT_ACCEL_MAX;
          const moveit::core::VariableBounds& b = rmodel.getVariableBounds(vars[j]);
          if (b.acceleration_bounded_)
            a_max = std::min(fabs(b.max_acceleration_ * acceleration_scaling_factor),
                             fabs(b.min_acceleration_ * acceleration_scaling_factor));
 
          if (index == 0)
          {
            // First point
            q1 = next_waypoint->getVariablePosition(idx[j]);
            q2 = curr_waypoint->getVariablePosition(idx[j]);
            q3 = next_waypoint->getVariablePosition(idx[j]);
 
            dt1 = dt2 = time_diff[index];
            assert(!backwards);
          }
          else if (index < num_points - 1)
          {
            // middle points
            q1 = prev_waypoint->getVariablePosition(idx[j]);
            q2 = curr_waypoint->getVariablePosition(idx[j]);
            q3 = next_waypoint->getVariablePosition(idx[j]);
 
            dt1 = time_diff[index - 1];
            dt2 = time_diff[index];
          }
          else
          {
            // last point - careful, there are only numpoints-1 time intervals
            q1 = prev_waypoint->getVariablePosition(idx[j]);
            q2 = curr_waypoint->getVariablePosition(idx[j]);
            q3 = prev_waypoint->getVariablePosition(idx[j]);
 
            dt1 = dt2 = time_diff[index - 1];
            assert(backwards);
          }
 
          if (dt1 == 0.0 || dt2 == 0.0)
          {
            v1 = 0.0;
            v2 = 0.0;
            a = 0.0;
          }
          else
          {
            bool start_velocity = false;
            if (index == 0)
            {
              if (curr_waypoint->hasVelocities())
              {
                start_velocity = true;
                v1 = curr_waypoint->getVariableVelocity(idx[j]);
              }
            }
            v1 = start_velocity ? v1 : (q2 - q1) / dt1;
            v2 = (q3 - q2) / dt2;
            a = 2.0 * (v2 - v1) / (dt1 + dt2);
          }
 
          if (fabs(a) > a_max + ROUNDING_THRESHOLD)
          {
            if (!backwards)
            {
              dt2 = std::min(dt2 + max_time_change_per_it_, findT2(q2 - q1, q3 - q2, dt1, dt2, a_max));
              time_diff[index] = dt2;
            }
            else
            {
              dt1 = std::min(dt1 + max_time_change_per_it_, findT1(q2 - q1, q3 - q2, dt1, dt2, a_max));
              time_diff[index - 1] = dt1;
            }
            num_updates++;
 
            if (dt1 == 0.0 || dt2 == 0.0)
            {
              v1 = 0.0;
              v2 = 0.0;
              a = 0.0;
            }
            else
            {
              v1 = (q2 - q1) / dt1;
              v2 = (q3 - q2) / dt2;
              a = 2 * (v2 - v1) / (dt1 + dt2);
            }
          }
        }
        backwards = !backwards;
      }
    }
    // ROS_DEBUG_NAMED("trajectory_processing.iterative_time_parameterization", "applyAcceleration: num_updates=%i",
    // num_updates);
  } while (num_updates > 0 && iteration < static_cast<int>(max_iterations_));
}
 
bool IterativeParabolicTimeParameterization::computeTimeStamps(robot_trajectory::RobotTrajectory& trajectory,
                                                               const double max_velocity_scaling_factor,
                                                               const double max_acceleration_scaling_factor) const
{
  if (trajectory.empty())
    return true;
 
  const moveit::core::JointModelGroup* group = trajectory.getGroup();
  if (!group)
  {
    ROS_ERROR_NAMED("trajectory_processing.iterative_time_parameterization", "It looks like the planner did not set "
                                                                             "the group the plan was computed for");
    return false;
  }
 
  // this lib does not actually work properly when angles wrap around, so we need to unwind the path first
  trajectory.unwind();
 
  const int num_points = trajectory.getWayPointCount();
  std::vector<double> time_diff(num_points - 1, 0.0);  // the time difference between adjacent points
 
  applyVelocityConstraints(trajectory, time_diff, max_velocity_scaling_factor);
  applyAccelerationConstraints(trajectory, time_diff, max_acceleration_scaling_factor);
 
  IterativeParabolicTimeParameterization::updateTrajectory(trajectory, time_diff);
  return true;
}
}  // namespace trajectory_processing