[wpilib] Add pose estimators (#2867)

Pose and state estimators can filter latency-compensated global measurements and fuse them with state-space drivetrain model information to estimate robot position. They are drop-in replacements for the existing odometry classes.

Co-authored-by: Declan Freeman-Gleason <declanfreemangleason@gmail.com>
Co-authored-by: Prateek Machiraju <prateek.machiraju@gmail.com>
Co-authored-by: Claudius Tewari <cttewari@gmail.com>
Co-authored-by: Matt <matthew.morley.ca@gmail.com>

wpilibcExamples/src/main/cpp/examples/DifferentialDrivePoseEstimator/cpp/Drivetrain.cpp

@@ -0,0 +1,45 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2019-2020 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 "Drivetrain.h"
+
+#include <frc2/Timer.h>
+
+#include "ExampleGlobalMeasurementSensor.h"
+
+void Drivetrain::SetSpeeds(const frc::DifferentialDriveWheelSpeeds& speeds) {
+  const auto leftFeedforward = m_feedforward.Calculate(speeds.left);
+  const auto rightFeedforward = m_feedforward.Calculate(speeds.right);
+  const double leftOutput = m_leftPIDController.Calculate(
+      m_leftEncoder.GetRate(), speeds.left.to<double>());
+  const double rightOutput = m_rightPIDController.Calculate(
+      m_rightEncoder.GetRate(), speeds.right.to<double>());
+
+  m_leftGroup.SetVoltage(units::volt_t{leftOutput} + leftFeedforward);
+  m_rightGroup.SetVoltage(units::volt_t{rightOutput} + rightFeedforward);
+}
+
+void Drivetrain::Drive(units::meters_per_second_t xSpeed,
+                       units::radians_per_second_t rot) {
+  SetSpeeds(m_kinematics.ToWheelSpeeds({xSpeed, 0_mps, rot}));
+}
+
+void Drivetrain::UpdateOdometry() {
+  m_poseEstimator.Update(m_gyro.GetRotation2d(),
+                         {units::meters_per_second_t(m_leftEncoder.GetRate()),
+                          units::meters_per_second_t(m_rightEncoder.GetRate())},
+                         units::meter_t(m_leftEncoder.GetDistance()),
+                         units::meter_t(m_rightEncoder.GetDistance()));
+
+  // Also apply vision measurements. We use 0.3 seconds in the past as an
+  // example -- on a real robot, this must be calculated based either on latency
+  // or timestamps.
+  m_poseEstimator.AddVisionMeasurement(
+      ExampleGlobalMeasurementSensor::GetEstimatedGlobalPose(
+          m_poseEstimator.GetEstimatedPosition()),
+      frc2::Timer::GetFPGATimestamp() - 0.3_s);
+}

wpilibcExamples/src/main/cpp/examples/DifferentialDrivePoseEstimator/cpp/Robot.cpp

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+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2019-2020 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/SlewRateLimiter.h>
+#include <frc/TimedRobot.h>
+#include <frc/XboxController.h>
+
+#include "Drivetrain.h"
+
+class Robot : public frc::TimedRobot {
+ public:
+  void AutonomousPeriodic() override {
+    TeleopPeriodic();
+    m_drive.UpdateOdometry();
+  }
+
+  void TeleopPeriodic() override {
+    // Get the x speed. We are inverting this because Xbox controllers return
+    // negative values when we push forward.
+    const auto xSpeed = -m_speedLimiter.Calculate(
+                            m_controller.GetY(frc::GenericHID::kLeftHand)) *
+                        Drivetrain::kMaxSpeed;
+
+    // Get the rate of angular rotation. We are inverting this because we want a
+    // positive value when we pull to the left (remember, CCW is positive in
+    // mathematics). Xbox controllers return positive values when you pull to
+    // the right by default.
+    const auto rot = -m_rotLimiter.Calculate(
+                         m_controller.GetX(frc::GenericHID::kRightHand)) *
+                     Drivetrain::kMaxAngularSpeed;
+
+    m_drive.Drive(xSpeed, rot);
+  }
+
+ private:
+  frc::XboxController m_controller{0};
+
+  // Slew rate limiters to make joystick inputs more gentle; 1/3 sec from 0
+  // to 1.
+  frc::SlewRateLimiter<units::scalar> m_speedLimiter{3 / 1_s};
+  frc::SlewRateLimiter<units::scalar> m_rotLimiter{3 / 1_s};
+
+  Drivetrain m_drive;
+};
+
+#ifndef RUNNING_FRC_TESTS
+int main() { return frc::StartRobot<Robot>(); }
+#endif

wpilibcExamples/src/main/cpp/examples/DifferentialDrivePoseEstimator/include/Drivetrain.h

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+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2019-2020 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 <frc/AnalogGyro.h>
+#include <frc/Encoder.h>
+#include <frc/PWMVictorSPX.h>
+#include <frc/SpeedControllerGroup.h>
+#include <frc/controller/PIDController.h>
+#include <frc/controller/SimpleMotorFeedforward.h>
+#include <frc/estimator/DifferentialDrivePoseEstimator.h>
+#include <frc/kinematics/DifferentialDriveKinematics.h>
+#include <units/angle.h>
+#include <units/angular_velocity.h>
+#include <units/length.h>
+#include <units/velocity.h>
+#include <wpi/math>
+
+/**
+ * Represents a differential drive style drivetrain.
+ */
+class Drivetrain {
+ public:
+  Drivetrain() {
+    m_gyro.Reset();
+    // Set the distance per pulse for the drive encoders. We can simply use the
+    // distance traveled for one rotation of the wheel divided by the encoder
+    // resolution.
+    m_leftEncoder.SetDistancePerPulse(
+        2 * wpi::math::pi * kWheelRadius.to<double>() / kEncoderResolution);
+    m_rightEncoder.SetDistancePerPulse(
+        2 * wpi::math::pi * kWheelRadius.to<double>() / kEncoderResolution);
+
+    m_leftEncoder.Reset();
+    m_rightEncoder.Reset();
+  }
+
+  static constexpr units::meters_per_second_t kMaxSpeed =
+      3.0_mps;  // 3 meters per second
+  static constexpr units::radians_per_second_t kMaxAngularSpeed{
+      wpi::math::pi};  // 1/2 rotation per second
+
+  void SetSpeeds(const frc::DifferentialDriveWheelSpeeds& speeds);
+  void Drive(units::meters_per_second_t xSpeed,
+             units::radians_per_second_t rot);
+  void UpdateOdometry();
+
+ private:
+  static constexpr units::meter_t kTrackWidth = 0.381_m * 2;
+  static constexpr units::meter_t kWheelRadius = 0.0508_m;
+  static constexpr int kEncoderResolution = 4096;
+
+  frc::PWMVictorSPX m_leftLeader{1};
+  frc::PWMVictorSPX m_leftFollower{2};
+  frc::PWMVictorSPX m_rightLeader{3};
+  frc::PWMVictorSPX m_rightFollower{4};
+
+  frc::SpeedControllerGroup m_leftGroup{m_leftLeader, m_leftFollower};
+  frc::SpeedControllerGroup m_rightGroup{m_rightLeader, m_rightFollower};
+
+  frc::Encoder m_leftEncoder{0, 1};
+  frc::Encoder m_rightEncoder{2, 3};
+
+  frc2::PIDController m_leftPIDController{1.0, 0.0, 0.0};
+  frc2::PIDController m_rightPIDController{1.0, 0.0, 0.0};
+
+  frc::AnalogGyro m_gyro{0};
+
+  frc::DifferentialDriveKinematics m_kinematics{kTrackWidth};
+
+  // Gains are for example purposes only - must be determined for your own
+  // robot!
+  frc::DifferentialDrivePoseEstimator m_poseEstimator{
+      frc::Rotation2d(),
+      frc::Pose2d(),
+      {0.01, 0.01, 0.01, 0.01, 0.01},
+      {0.1, 0.1, 0.1},
+      {0.1, 0.1, 0.1}};
+
+  // Gains are for example purposes only - must be determined for your own
+  // robot!
+  frc::SimpleMotorFeedforward<units::meters> m_feedforward{1_V, 3_V / 1_mps};
+};

wpilibcExamples/src/main/cpp/examples/DifferentialDrivePoseEstimator/include/ExampleGlobalMeasurementSensor.h

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+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2020 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 <frc/StateSpaceUtil.h>
+#include <frc/geometry/Pose2d.h>
+
+/**
+ * This dummy class represents a global measurement sensor, such as a computer
+ * vision solution.
+ */
+class ExampleGlobalMeasurementSensor {
+ public:
+  static frc::Pose2d GetEstimatedGlobalPose(
+      const frc::Pose2d& estimatedRobotPose) {
+    auto randVec = frc::MakeWhiteNoiseVector(0.1, 0.1, 0.1);
+    return frc::Pose2d(estimatedRobotPose.X() + units::meter_t(randVec(0)),
+                       estimatedRobotPose.Y() + units::meter_t(randVec(1)),
+                       estimatedRobotPose.Rotation() +
+                           frc::Rotation2d(units::radian_t(randVec(3))));
+  }
+};