Make QuaternionToTwist.RotationAxis configuration property (#12)

* Make QuaternionToTwist.RotationAxis configuration property

- Mark its category as such
- Rename some of the internal variables in QuaternionToTwist to reflect
  their true meaning

* Forgot to rename one variable in QuaternionToTwist

Author: jonnew

OpenEphys.Commutator/Defintions.cs

@@ -0,0 +1,8 @@
+namespace OpenEphys.Commutator
+{
+    static class Definitions
+    {
+        internal const string ConfigurationCategory = "Configuration";
+        internal const string AcquisitionCategory = "Acquisition";
+    }
+}

OpenEphys.Commutator/QuaternionToTwist.cs

@@ -23,6 +23,7 @@ public class QuaternionToTwist : Combinator<Quaternion, double>
         /// in the direction that the tether exits the headstage. Note that negating this vector will result in
         /// negating the direction of twisting.
         /// </remarks>
+        [Category(Definitions.ConfigurationCategory)]
         [TypeConverter(typeof(NumericRecordConverter))]
         [Description("The direction vector specifying the axis around which to calculate the twist.")]
         public Vector3 RotationAxis { get; set; } = Vector3.UnitZ;
@@ -35,30 +36,31 @@ public class QuaternionToTwist : Combinator<Quaternion, double>
         /// <returns>The sequence of twist values, in units of turns.</returns>
         public override IObservable<double> Process(IObservable<Quaternion> source)
         {
+            var rotationAxis = RotationAxis;
+
             return Observable.Defer(() =>
             {
-                double? previousTwist = default;
+                double? previousAngleAboutAxis = default;
                 return source.Select(rotation =>
                 {
                     // project rotation axis onto the direction axis
-                    var direction = RotationAxis;
-                    var rotationAxis = new Vector3(rotation.X, rotation.Y, rotation.Z);
-                    var dotProduct = Vector3.Dot(rotationAxis, direction);
-                    var projection = dotProduct / Vector3.Dot(direction, direction) * direction;
-                    var twist = new Quaternion(projection, rotation.W);
-                    twist = Quaternion.Normalize(twist);
+                    var vectorPart = new Vector3(rotation.X, rotation.Y, rotation.Z);
+                    var dotProduct = Vector3.Dot(vectorPart, rotationAxis);
+                    var projection = dotProduct / Vector3.Dot(rotationAxis, rotationAxis) * rotationAxis;
+                    var rotationAboutAxis = new Quaternion(projection, rotation.W);
+                    rotationAboutAxis = Quaternion.Normalize(rotationAboutAxis);
                     if (dotProduct < 0) // account for angle-axis flipping
                     {
-                        twist = -twist;
+                        rotationAboutAxis = -rotationAboutAxis;
                     }
 
                     // normalize twist feedback in units of turns
-                    var twistAngle = 2 * Math.Acos(twist.W);
-                    var feedback = previousTwist.HasValue
-                        ? (twistAngle - previousTwist.GetValueOrDefault() + 3 * Math.PI) % (2 * Math.PI) - Math.PI
+                    var angleAboutAxis = 2 * Math.Acos(rotationAboutAxis.W);
+                    var twist = previousAngleAboutAxis.HasValue
+                        ? (angleAboutAxis - previousAngleAboutAxis.GetValueOrDefault() + 3 * Math.PI) % (2 * Math.PI) - Math.PI
                         : 0;
-                    previousTwist = twistAngle;
-                    return -feedback / (2 * Math.PI);
+                    previousAngleAboutAxis = angleAboutAxis;
+                    return -twist / (2 * Math.PI);
                 });
             });
         }

OpenEphys.Commutator/SerialCommutator.cs

@@ -14,16 +14,14 @@ namespace OpenEphys.Commutator
     [Description("Controls an Open Ephys commutator using a serial port.")]
     public class SerialCommutator : Combinator<double, string>
     {
-        const string ConfigurationCategory = "Configuration";
-        const string AcquisitionCategory = "Acquisition";
 
         readonly BehaviorSubject<bool> enabled = new(true);
         readonly BehaviorSubject<bool> led = new(true);
 
         /// <summary>
         /// Gets or sets the name of the serial port.
         /// </summary>
-        [Category(ConfigurationCategory)]
+        [Category(Definitions.ConfigurationCategory)]
         [TypeConverter(typeof(PortNameConverter))]
         [Description("The name of the serial port.")]
         public string PortName { get; set; }
@@ -35,7 +33,7 @@ public class SerialCommutator : Combinator<double, string>
         /// If true, the commutator will activate the motor and respond to turn commands. If false,
         /// the motor driver will be deactivated and motion commands will be ignored.
         /// </remarks>
-        [Category(AcquisitionCategory)]
+        [Category(Definitions.AcquisitionCategory)]
         [Description("If true, the commutator will be enabled. If false, it will disable the motor and ignore motion commands.")]
         public bool Enable
         {
@@ -50,7 +48,7 @@ public bool Enable
         /// If true, the commutator indication LED turn on. If false, the indication LED will turn
         /// off.
         /// </remarks>
-        [Category(AcquisitionCategory)]
+        [Category(Definitions.AcquisitionCategory)]
         [Description("If true, the commutator indication LED turn on. If false, the indication LED will turn off.")]
         public bool EnableLed
         {