Add TrapezoidProfile class (#1673)

wpilibc/src/main/native/cpp/trajectory/TrapezoidProfile.cpp

@@ -0,0 +1,158 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2019 FIRST. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "frc/trajectory/TrapezoidProfile.h"
+
+using namespace frc;
+
+TrapezoidProfile::TrapezoidProfile(Constraints constraints, State goal,
+                                   State initial)
+    : m_direction{ShouldFlipAcceleration(initial, goal) ? -1 : 1},
+      m_constraints(constraints),
+      m_initial(Direct(initial)),
+      m_goal(Direct(goal)) {
+  if (m_initial.velocity > m_constraints.maxVelocity) {
+    m_initial.velocity = m_constraints.maxVelocity;
+  }
+
+  // Deal with a possibly truncated motion profile (with nonzero initial or
+  // final velocity) by calculating the parameters as if the profile began and
+  // ended at zero velocity
+  units::second_t cutoffBegin =
+      m_initial.velocity / m_constraints.maxAcceleration;
+  units::meter_t cutoffDistBegin =
+      cutoffBegin * cutoffBegin * m_constraints.maxAcceleration / 2.0;
+
+  units::second_t cutoffEnd = m_goal.velocity / m_constraints.maxAcceleration;
+  units::meter_t cutoffDistEnd =
+      cutoffEnd * cutoffEnd * m_constraints.maxAcceleration / 2.0;
+
+  // Now we can calculate the parameters as if it was a full trapezoid instead
+  // of a truncated one
+
+  units::meter_t fullTrapezoidDist =
+      cutoffDistBegin + (m_goal.position - m_initial.position) + cutoffDistEnd;
+  units::second_t accelerationTime =
+      m_constraints.maxVelocity / m_constraints.maxAcceleration;
+
+  units::meter_t fullSpeedDist =
+      fullTrapezoidDist -
+      accelerationTime * accelerationTime * m_constraints.maxAcceleration;
+
+  // Handle the case where the profile never reaches full speed
+  if (fullSpeedDist < 0_m) {
+    accelerationTime =
+        units::math::sqrt(fullTrapezoidDist / m_constraints.maxAcceleration);
+    fullSpeedDist = 0_m;
+  }
+
+  m_endAccel = accelerationTime - cutoffBegin;
+  m_endFullSpeed = m_endAccel + fullSpeedDist / m_constraints.maxVelocity;
+  m_endDeccel = m_endFullSpeed + accelerationTime - cutoffEnd;
+}
+
+TrapezoidProfile::State TrapezoidProfile::Calculate(units::second_t t) const {
+  State result = m_initial;
+
+  if (t < m_endAccel) {
+    result.velocity += t * m_constraints.maxAcceleration;
+    result.position +=
+        (m_initial.velocity + t * m_constraints.maxAcceleration / 2.0) * t;
+  } else if (t < m_endFullSpeed) {
+    result.velocity = m_constraints.maxVelocity;
+    result.position += (m_initial.velocity +
+                        m_endAccel * m_constraints.maxAcceleration / 2.0) *
+                           m_endAccel +
+                       m_constraints.maxVelocity * (t - m_endAccel);
+  } else if (t <= m_endDeccel) {
+    result.velocity =
+        m_goal.velocity + (m_endDeccel - t) * m_constraints.maxAcceleration;
+    units::second_t timeLeft = m_endDeccel - t;
+    result.position =
+        m_goal.position -
+        (m_goal.velocity + timeLeft * m_constraints.maxAcceleration / 2.0) *
+            timeLeft;
+  } else {
+    result = m_goal;
+  }
+
+  return Direct(result);
+}
+
+units::second_t TrapezoidProfile::TimeLeftUntil(units::meter_t target) const {
+  units::meter_t position = m_initial.position * m_direction;
+  units::meters_per_second_t velocity = m_initial.velocity * m_direction;
+
+  units::second_t endAccel = m_endAccel * m_direction;
+  units::second_t endFullSpeed = m_endFullSpeed * m_direction - endAccel;
+
+  if (target < position) {
+    endAccel *= -1.0;
+    endFullSpeed *= -1.0;
+    velocity *= -1.0;
+  }
+
+  endAccel = units::math::max(endAccel, 0_s);
+  endFullSpeed = units::math::max(endFullSpeed, 0_s);
+  units::second_t endDeccel = m_endDeccel - endAccel - endFullSpeed;
+  endDeccel = units::math::max(endDeccel, 0_s);
+
+  const units::meters_per_second_squared_t acceleration =
+      m_constraints.maxAcceleration;
+  const units::meters_per_second_squared_t decceleration =
+      -m_constraints.maxAcceleration;
+
+  units::meter_t distToTarget = units::math::abs(target - position);
+
+  if (distToTarget < 1e-6_m) {
+    return 0_s;
+  }
+
+  units::meter_t accelDist =
+      velocity * endAccel + 0.5 * acceleration * endAccel * endAccel;
+
+  units::meters_per_second_t deccelVelocity;
+  if (endAccel > 0_s) {
+    deccelVelocity = units::math::sqrt(
+        units::math::abs(velocity * velocity + 2 * acceleration * accelDist));
+  } else {
+    deccelVelocity = velocity;
+  }
+
+  units::meter_t deccelDist =
+      deccelVelocity * endDeccel + 0.5 * decceleration * endDeccel * endDeccel;
+
+  deccelDist = units::math::max(deccelDist, 0_m);
+
+  units::meter_t fullSpeedDist = m_constraints.maxVelocity * endFullSpeed;
+
+  if (accelDist > distToTarget) {
+    accelDist = distToTarget;
+    fullSpeedDist = 0_m;
+    deccelDist = 0_m;
+  } else if (accelDist + fullSpeedDist > distToTarget) {
+    fullSpeedDist = distToTarget - accelDist;
+    deccelDist = 0_m;
+  } else {
+    deccelDist = distToTarget - fullSpeedDist - accelDist;
+  }
+
+  units::second_t accelTime =
+      (-velocity + units::math::sqrt(units::math::abs(
+                       velocity * velocity + 2 * acceleration * accelDist))) /
+      acceleration;
+
+  units::second_t deccelTime =
+      (-deccelVelocity +
+       units::math::sqrt(units::math::abs(deccelVelocity * deccelVelocity +
+                                          2 * decceleration * deccelDist))) /
+      decceleration;
+
+  units::second_t fullSpeedTime = fullSpeedDist / m_constraints.maxVelocity;
+
+  return accelTime + fullSpeedTime + deccelTime;
+}

wpilibc/src/main/native/include/frc/trajectory/TrapezoidProfile.h

@@ -0,0 +1,134 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2019 FIRST. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include <units/units.h>
+
+namespace frc {
+
+/**
+ * A trapezoid-shaped velocity profile.
+ *
+ * While this class can be used for a profiled movement from start to finish,
+ * the intended usage is to filter a reference's dynamics based on trapezoidal
+ * velocity constraints. To compute the reference obeying this constraint, do
+ * the following.
+ *
+ * Initialization:
+ * @code{.cpp}
+ * TrapezoidalMotionProfile::Constraints constraints{kMaxV, kMaxA};
+ * double previousProfiledReference = initialReference;
+ * @endcode
+ *
+ * Run on update:
+ * @code{.cpp}
+ * TrapezoidalMotionProfile profile{constraints, unprofiledReference,
+ *                                  previousProfiledReference};
+ * previousProfiledReference = profile.Calculate(timeSincePreviousUpdate);
+ * @endcode
+ *
+ * where `unprofiledReference` is free to change between calls. Note that when
+ * the unprofiled reference is within the constraints, `Calculate()` returns the
+ * unprofiled reference unchanged.
+ *
+ * Otherwise, a timer can be started to provide monotonic values for
+ * `Calculate()` and to determine when the profile has completed via
+ * `IsFinished()`.
+ */
+class TrapezoidProfile {
+ public:
+  class Constraints {
+   public:
+    units::meters_per_second_t maxVelocity = 0_mps;
+    units::meters_per_second_squared_t maxAcceleration = 0_mps_sq;
+  };
+
+  class State {
+   public:
+    units::meter_t position = 0_m;
+    units::meters_per_second_t velocity = 0_mps;
+    bool operator==(const State& rhs) const {
+      return position == rhs.position && velocity == rhs.velocity;
+    }
+    bool operator!=(const State& rhs) const { return !(*this == rhs); }
+  };
+
+  /**
+   * Construct a TrapezoidProfile.
+   *
+   * @param constraints The constraints on the profile, like maximum velocity.
+   * @param goal        The desired state when the profile is complete.
+   * @param initial     The initial state (usually the current state).
+   */
+  TrapezoidProfile(Constraints constraints, State goal,
+                   State initial = State{0_m, 0_mps});
+
+  /**
+   * Calculate the correct position and velocity for the profile at a time t
+   * where the beginning of the profile was at time t = 0.
+   *
+   * @param t The time since the beginning of the profile.
+   */
+  State Calculate(units::second_t t) const;
+
+  /**
+   * Returns the time left until a target distance in the profile is reached.
+   *
+   * @param target The target distance.
+   */
+  units::second_t TimeLeftUntil(units::meter_t target) const;
+
+  /**
+   * Returns the total time the profile takes to reach the goal.
+   */
+  units::second_t TotalTime() const { return m_endDeccel; }
+
+  /**
+   * Returns true if the profile has reached the goal.
+   *
+   * The profile has reached the goal if the time since the profile started
+   * has exceeded the profile's total time.
+   *
+   * @param t The time since the beginning of the profile.
+   */
+  bool IsFinished(units::second_t t) const { return t >= TotalTime(); }
+
+ private:
+  /**
+   * Returns true if the profile inverted.
+   *
+   * The profile is inverted if goal position is less than the initial position.
+   *
+   * @param initial The initial state (usually the current state).
+   * @param goal    The desired state when the profile is complete.
+   */
+  static bool ShouldFlipAcceleration(const State& initial, const State& goal) {
+    return initial.position > goal.position;
+  }
+
+  // Flip the sign of the velocity and position if the profile is inverted
+  State Direct(const State& in) const {
+    State result = in;
+    result.position *= m_direction;
+    result.velocity *= m_direction;
+    return result;
+  }
+
+  // The direction of the profile, either 1 for forwards or -1 for inverted
+  int m_direction;
+
+  Constraints m_constraints;
+  State m_initial;
+  State m_goal;
+
+  units::second_t m_endAccel;
+  units::second_t m_endFullSpeed;
+  units::second_t m_endDeccel;
+};
+
+}  // namespace frc