[wpimath] Remove Rotation2d value field

It's not part of SO(2).

wpimath/src/main/java/edu/wpi/first/math/geometry/Rotation2d.java

@@ -23,10 +23,6 @@
 
 /**
  * A rotation in a 2D coordinate frame represented by a point on the unit circle (cosine and sine).
- *
- * <p>The angle is continuous, that is if a Rotation2d is constructed with 361 degrees, it will
- * return 361 degrees. This allows algorithms that wouldn't want to see a discontinuity in the
- * rotations as it sweeps past from 360 to 0 on the second time around.
  */
 @JsonIgnoreProperties(ignoreUnknown = true)
 @JsonAutoDetect(getterVisibility = JsonAutoDetect.Visibility.NONE)
@@ -81,13 +77,11 @@ public class Rotation2d
    */
   public static final Rotation2d k180deg = kPi;
 
-  private final double m_value;
   private final double m_cos;
   private final double m_sin;
 
   /** Constructs a Rotation2d with a default angle of 0 degrees. */
   public Rotation2d() {
-    m_value = 0.0;
     m_cos = 1.0;
     m_sin = 0.0;
   }
@@ -99,7 +93,6 @@ public Rotation2d() {
    */
   @JsonCreator
   public Rotation2d(@JsonProperty(required = true, value = "radians") double value) {
-    m_value = value;
     m_cos = Math.cos(value);
     m_sin = Math.sin(value);
   }
@@ -121,7 +114,6 @@ public Rotation2d(double x, double y) {
       MathSharedStore.reportError(
           "x and y components of Rotation2d are zero\n", Thread.currentThread().getStackTrace());
     }
-    m_value = Math.atan2(m_sin, m_cos);
   }
 
   /**
@@ -196,7 +188,7 @@ public Rotation2d minus(Rotation2d other) {
    * @return The inverse of the current rotation.
    */
   public Rotation2d unaryMinus() {
-    return new Rotation2d(-m_value);
+    return new Rotation2d(m_cos, -m_sin);
   }
 
   /**
@@ -206,7 +198,7 @@ public Rotation2d unaryMinus() {
    * @return The new scaled Rotation2d.
    */
   public Rotation2d times(double scalar) {
-    return new Rotation2d(m_value * scalar);
+    return new Rotation2d(getRadians() * scalar);
   }
 
   /**
@@ -248,25 +240,22 @@ public Angle getMeasure() {
   }
 
   /**
-   * Returns the radian value of the Rotation2d.
+   * Returns the radian value of the Rotation2d constrained within [-π, π].
    *
-   * @return The radian value of the Rotation2d.
-   * @see edu.wpi.first.math.MathUtil#angleModulus(double) to constrain the angle within (-π, π]
+   * @return The radian value of the Rotation2d constrained within [-π, π].
    */
   @JsonProperty
   public double getRadians() {
-    return m_value;
+    return Math.atan2(m_sin, m_cos);
   }
 
   /**
-   * Returns the degree value of the Rotation2d.
+   * Returns the degree value of the Rotation2d constrained within [-180, 180].
    *
-   * @return The degree value of the Rotation2d.
-   * @see edu.wpi.first.math.MathUtil#inputModulus(double, double, double) to constrain the angle
-   *     within (-180, 180]
+   * @return The degree value of the Rotation2d constrained within [-180, 180].
    */
   public double getDegrees() {
-    return Math.toDegrees(m_value);
+    return Math.toDegrees(getRadians());
   }
 
   /**
@@ -275,7 +264,7 @@ public double getDegrees() {
    * @return The number of rotations of the Rotation2d.
    */
   public double getRotations() {
-    return Units.radiansToRotations(m_value);
+    return Units.radiansToRotations(getRadians());
   }
 
   /**
@@ -307,7 +296,7 @@ public double getTan() {
 
   @Override
   public String toString() {
-    return String.format("Rotation2d(Rads: %.2f, Deg: %.2f)", m_value, Math.toDegrees(m_value));
+    return String.format("Rotation2d(Rads: %.2f, Deg: %.2f)", getRadians(), getDegrees());
   }
 
   /**
@@ -324,7 +313,7 @@ public boolean equals(Object obj) {
 
   @Override
   public int hashCode() {
-    return Objects.hash(m_value);
+    return Objects.hash(getRadians());
   }
 
   @Override

wpimath/src/main/native/include/frc/geometry/Rotation2d.h

@@ -19,11 +19,6 @@ namespace frc {
 /**
  * A rotation in a 2D coordinate frame represented by a point on the unit circle
  * (cosine and sine).
- *
- * The angle is continuous, that is if a Rotation2d is constructed with 361
- * degrees, it will return 361 degrees. This allows algorithms that wouldn't
- * want to see a discontinuity in the rotations as it sweeps past from 360 to 0
- * on the second time around.
  */
 class WPILIB_DLLEXPORT Rotation2d {
  public:
@@ -38,8 +33,7 @@ class WPILIB_DLLEXPORT Rotation2d {
    * @param value The value of the angle.
    */
   constexpr Rotation2d(units::angle_unit auto value)  // NOLINT
-      : m_value{value},
-        m_cos{gcem::cos(value.template convert<units::radian>().value())},
+      : m_cos{gcem::cos(value.template convert<units::radian>().value())},
         m_sin{gcem::sin(value.template convert<units::radian>().value())} {}
 
   /**
@@ -63,7 +57,6 @@ class WPILIB_DLLEXPORT Rotation2d {
             wpi::GetStackTrace(1));
       }
     }
-    m_value = units::radian_t{gcem::atan2(m_sin, m_cos)};
   }
 
   /**
@@ -102,7 +95,7 @@ class WPILIB_DLLEXPORT Rotation2d {
    *
    * @return The inverse of the current rotation.
    */
-  constexpr Rotation2d operator-() const { return Rotation2d{-m_value}; }
+  constexpr Rotation2d operator-() const { return Rotation2d{m_cos, -m_sin}; }
 
   /**
    * Multiplies the current rotation by a scalar.
@@ -112,7 +105,7 @@ class WPILIB_DLLEXPORT Rotation2d {
    * @return The new scaled Rotation2d.
    */
   constexpr Rotation2d operator*(double scalar) const {
-    return Rotation2d{m_value * scalar};
+    return Rotation2d{Radians() * scalar};
   }
 
   /**
@@ -155,20 +148,20 @@ class WPILIB_DLLEXPORT Rotation2d {
   }
 
   /**
-   * Returns the radian value of the rotation.
+   * Returns the radian value of the rotation constrained within [-π, π].
    *
-   * @return The radian value of the rotation.
-   * @see AngleModulus to constrain the angle within (-π, π]
+   * @return The radian value of the rotation constrained within [-π, π].
    */
-  constexpr units::radian_t Radians() const { return m_value; }
+  constexpr units::radian_t Radians() const {
+    return units::radian_t{gcem::atan2(m_sin, m_cos)};
+  }
 
   /**
-   * Returns the degree value of the rotation.
+   * Returns the degree value of the rotation constrained within [-180, 180].
    *
-   * @return The degree value of the rotation.
-   * @see InputModulus to constrain the angle within (-180, 180]
+   * @return The degree value of the rotation constrained within [-180, 180].
    */
-  constexpr units::degree_t Degrees() const { return m_value; }
+  constexpr units::degree_t Degrees() const { return Radians(); }
 
   /**
    * Returns the cosine of the rotation.
@@ -192,7 +185,6 @@ class WPILIB_DLLEXPORT Rotation2d {
   constexpr double Tan() const { return Sin() / Cos(); }
 
  private:
-  units::radian_t m_value = 0_rad;
   double m_cos = 1;
   double m_sin = 0;
 };

wpimath/src/test/java/edu/wpi/first/math/geometry/Rotation2dTest.java

@@ -79,7 +79,7 @@ void testMultiply() {
     var rot = Rotation2d.fromDegrees(10.0);
 
     assertEquals(30.0, rot.times(3.0).getDegrees(), kEpsilon);
-    assertEquals(410.0, rot.times(41.0).getDegrees(), kEpsilon);
+    assertEquals(50.0, rot.times(41.0).getDegrees(), kEpsilon);
   }
 
   @Test

wpimath/src/test/java/edu/wpi/first/math/kinematics/SwerveDriveKinematicsTest.java

@@ -138,7 +138,7 @@ void testResetWheelAngle() {
         () -> assertEquals(0.0, moduleStates[0].angle.getDegrees(), kEpsilon),
         () -> assertEquals(90.0, moduleStates[1].angle.getDegrees(), kEpsilon),
         () -> assertEquals(180.0, moduleStates[2].angle.getDegrees(), kEpsilon),
-        () -> assertEquals(270.0, moduleStates[3].angle.getDegrees(), kEpsilon));
+        () -> assertEquals(-90.0, moduleStates[3].angle.getDegrees(), kEpsilon));
   }
 
   @Test

wpimath/src/test/native/cpp/geometry/Rotation2dTest.cpp

@@ -59,7 +59,7 @@ TEST(Rotation2dTest, Multiply) {
   const auto rot = Rotation2d{10_deg};
 
   EXPECT_DOUBLE_EQ(30.0, (rot * 3.0).Degrees().value());
-  EXPECT_DOUBLE_EQ(410.0, (rot * 41.0).Degrees().value());
+  EXPECT_DOUBLE_EQ(50.0, (rot * 41.0).Degrees().value());
 }
 
 TEST(Rotation2dTest, Equality) {
@@ -90,9 +90,9 @@ TEST(Rotation2dTest, Constexpr) {
   constexpr auto subtracted = cartesianCtor - degreeCtor;
 
   static_assert(defaultCtor.Radians() == 0_rad);
-  static_assert(degreeCtor.Degrees() == 270_deg);
-  static_assert(negated.Radians() == -5_rad);
-  static_assert(multiplied.Radians() == 10_rad);
+  static_assert(degreeCtor.Degrees() == -90_deg);
+  static_assert(negated.Radians() == -5_rad + 1_tr);
+  static_assert(multiplied.Radians() == 10_rad - 2_tr);
   static_assert(subtracted == rotation45);
   static_assert(radianCtor != degreeCtor);
 }

wpimath/src/test/native/cpp/kinematics/SwerveDriveKinematicsTest.cpp

@@ -143,7 +143,7 @@ TEST_F(SwerveDriveKinematicsTest, ResetWheelAngle) {
   EXPECT_NEAR(flMod.angle.Degrees().value(), 0.0, kEpsilon);
   EXPECT_NEAR(frMod.angle.Degrees().value(), 90.0, kEpsilon);
   EXPECT_NEAR(blMod.angle.Degrees().value(), 180.0, kEpsilon);
-  EXPECT_NEAR(brMod.angle.Degrees().value(), 270.0, kEpsilon);
+  EXPECT_NEAR(brMod.angle.Degrees().value(), -90.0, kEpsilon);
 }
 
 TEST_F(SwerveDriveKinematicsTest, TurnInPlaceForwardKinematics) {