[wpimath] ChassisSpeeds: document that values aren't relative to the …

…robot (NFC) (wpilibsuite#5551)

wpimath/src/main/java/edu/wpi/first/math/kinematics/ChassisSpeeds.java

@@ -8,20 +8,19 @@
 import edu.wpi.first.math.geometry.Rotation2d;
 
 /**
- * Represents the speed of a robot chassis. Although this struct contains similar members compared
- * to a Twist2d, they do NOT represent the same thing. Whereas a Twist2d represents a change in pose
- * w.r.t to the robot frame of reference, this ChassisSpeeds struct represents a velocity w.r.t to
- * the robot frame of reference.
+ * Represents the speed of a robot chassis. Although this class contains similar members compared to
+ * a Twist2d, they do NOT represent the same thing. Whereas a Twist2d represents a change in pose
+ * w.r.t to the robot frame of reference, a ChassisSpeeds object represents a robot's velocity.
  *
  * <p>A strictly non-holonomic drivetrain, such as a differential drive, should never have a dy
  * component because it can never move sideways. Holonomic drivetrains such as swerve and mecanum
  * will often have all three components.
  */
 public class ChassisSpeeds {
-  /** Represents forward velocity w.r.t the robot frame of reference. (Fwd is +) */
+  /** Velocity along the x-axis. (Fwd is +) */
   public double vxMetersPerSecond;
 
-  /** Represents sideways velocity w.r.t the robot frame of reference. (Left is +) */
+  /** Velocity along the y-axis. (Left is +) */
   public double vyMetersPerSecond;
 
   /** Represents the angular velocity of the robot frame. (CCW is +) */

wpimath/src/main/native/include/frc/kinematics/ChassisSpeeds.h

@@ -16,21 +16,20 @@ namespace frc {
  * Represents the speed of a robot chassis. Although this struct contains
  * similar members compared to a Twist2d, they do NOT represent the same thing.
  * Whereas a Twist2d represents a change in pose w.r.t to the robot frame of
- * reference, this ChassisSpeeds struct represents a velocity w.r.t to the robot
- * frame of reference.
+ * reference, a ChassisSpeeds struct represents a robot's velocity.
  *
  * A strictly non-holonomic drivetrain, such as a differential drive, should
  * never have a dy component because it can never move sideways. Holonomic
  * drivetrains such as swerve and mecanum will often have all three components.
  */
 struct WPILIB_DLLEXPORT ChassisSpeeds {
   /**
-   * Represents forward velocity w.r.t the robot frame of reference. (Fwd is +)
+   * Velocity along the x-axis. (Fwd is +)
    */
   units::meters_per_second_t vx = 0_mps;
 
   /**
-   * Represents strafe velocity w.r.t the robot frame of reference. (Left is +)
+   * Velocity along the y-axis. (Left is +)
    */
   units::meters_per_second_t vy = 0_mps;