Itermediate state. Do not use!

Frame.cs

@@ -105,9 +105,7 @@ public interface IFrame
         [field: FieldOffset(28)] public readonly float UnknownAt28 { get; } // (28)
         [field: FieldOffset(32)] public readonly float UnknownAt32 { get; } // (32)
         [field: FieldOffset(36)] public readonly float UnknownAt36 { get; } // (36)
-
         [field: FieldOffset(40)] public readonly uint HardwareTime { get; } // (40)
-
         [field: FieldOffset(44)] public readonly uint LengthOfEchoData { get; } // (44)
         [field: FieldOffset(48)] public readonly float WaterDepth { get; } // (48)
         [field: FieldOffset(52)] public readonly Frequency Frequency { get; } // (52)
@@ -119,15 +117,16 @@ public interface IFrame
         [field: FieldOffset(72)] public readonly float UnknownAt72 { get; } // (72)
         [field: FieldOffset(76)] public readonly float UnknownAt76 { get; } // (76)
         [field: FieldOffset(80)] public readonly float UnknownAt80 { get; } // (80)
-
         [field: FieldOffset(84)] public readonly float GNSSSpeed { get; } // (84)
         [field: FieldOffset(88)] public readonly float WaterTemperature { get; }  // (88)
-
         [field: FieldOffset(92)] public readonly int X { get; } // (92)
         [field: FieldOffset(96)] public readonly int Y { get; } // (96)
-
         [field: FieldOffset(100)] public readonly float WaterSpeed { get; } // (100)
-
+        /// <summary>
+        /// Heading of the vessel, calculation based on GNSS readings only.
+        /// (No drift was taken into account.) Unit: radians. Direction: azimuthal (↻⁻;
+        /// north is zero or 2·π, east is π/2.)
+        /// </summary>
         [field: FieldOffset(104)] public readonly float GNSSHeading { get; } // (104)
         [field: FieldOffset(108)] public readonly float GNSSAltitude { get; } // (108)
         [field: FieldOffset(112)] public readonly float MagneticHeading { get; } // (112)
@@ -260,7 +259,14 @@ private readonly string GetDebuggerDisplay() =>
         #region Unpack support
         public (double x, double y, double v, double t, double d) UnpackNavParameters()
         {
-            return (X, Y, (1825d / 3600d) * GNSSSpeed, Milliseconds / 1000d, (double.Pi / 2d) - GNSSHeading);
+            const double KnotsToMPS = 1852d / 3600d;
+            const double HalfPI = double.Pi / 2d;
+            const double MillisecondsToSeconds = 1d / 1000d;
+
+            return (X, Y,
+                    KnotsToMPS * GNSSSpeed,
+                    MillisecondsToSeconds * Milliseconds,
+                    HalfPI - GNSSHeading);
         }
         #endregion Unpack support
     }

SL3Reader.cs

@@ -7,6 +7,7 @@
 using System.Threading;
 using static System.Runtime.InteropServices.NativeMemory;
 using Microsoft.Win32.SafeHandles;
+using System.Numerics;
 
 namespace SL3Reader
 {
@@ -55,6 +56,16 @@ private List<IFrame> CreateNewFrameList(IEnumerable<IFrame> collection)
 
         #endregion Frame support
 
+        #region Augmented Coordinates
+        private List<Vector2> augmentedCoordinates;
+        public List<Vector2> AugmentedCoordinates => augmentedCoordinates ??= CreateNewCoordinateList();
+        private List<Vector2> CreateNewCoordinateList()
+        {
+            const long averageFrameSize = 2118L; // Empirically set value to avoid frequent resize of the underlying array.
+            return new((int)(Length / averageFrameSize));
+        }
+        #endregion Augmented Coordinates
+
         #region Indices
         private SortedDictionary<SurveyType, List<IFrame>> indexByType;
         private SortedDictionary<uint, List<IFrame>> indexByCampaign;
@@ -347,28 +358,29 @@ public unsafe void Export3D(string path)
 
         internal void AugmentTrajectory()
         {
-            using StreamWriter streamWriter = File.CreateText(@"F:\ox.csv");
-            streamWriter.WriteLine("X,Y");
+            const double lim = 1.2d;
+            const double C = 1.4326d; // Emirical
+
+            List<Vector2> crds = AugmentedCoordinates;
 
             int frameCount = Frames.Count; // Initialize the frames.
             if (frameCount < 1) return;
 
             (double x, double y, double v, double t, double d) =
                 Frames[0].UnpackNavParameters();
-            streamWriter.WriteLine(x.ToString() + "," + y.ToString());
+            crds.Add(new((float)x, (float)y));
+
             for (int i = 1; i < frameCount; i++)
             {
-                const double lim = 1.2d;
-                const double gyk = 1.4326d; // Emirical
                 IFrame frame = Frames[i];
                 (double nx, double ny, double nv, double nt, double nd) =
                     frame.UnpackNavParameters();
-                double sv = nv + nv, dt = nt - t;
-                double vec = gyk * .5d * sv * dt, ad = (nv * nd + v * d) / sv;
-                (double Sin, double Cos) = double.SinCos(ad);
+                double sv = v + nv, dt = nt - t;
+                double vec = C * .5d * sv * dt, ad = (nv * nd + v * d) / sv;
+                (double sin, double cos) = double.SinCos(ad);
 
-                y = double.FusedMultiplyAdd(vec, Sin, y);
-                x = double.FusedMultiplyAdd(vec, Cos, x);
+                y = double.FusedMultiplyAdd(vec, sin, y);
+                x = double.FusedMultiplyAdd(vec, cos, x);
                 t = nt;
                 v = nv;
                 d = nd;
@@ -384,7 +396,7 @@ internal void AugmentTrajectory()
                     if (double.Abs(dx) > lim)
                         x = nx + double.CopySign(lim, dx);
                 }
-                streamWriter.WriteLine(x.ToString() + "," + y.ToString());
+                crds.Add(new((float)x, (float)y));
             }
         }