1 files changed, 104 insertions, 24 deletions
diff --git a/android-app/app/src/main/kotlin/org/terst/nav/track/TackDetector.kt b/android-app/app/src/main/kotlin/org/terst/nav/track/TackDetector.kt
index b0d256b..763e693 100644
--- a/android-app/app/src/main/kotlin/org/terst/nav/track/TackDetector.kt
+++ b/android-app/app/src/main/kotlin/org/terst/nav/track/TackDetector.kt
@@ -1,50 +1,130 @@
 package org.terst.nav.track
 
 import kotlin.math.abs
+import kotlin.math.atan2
+import kotlin.math.cos
+import kotlin.math.sin
 
+/**
+ * Detects tacks and jibes in a recorded GPS track.
+ *
+ * A tack or jibe has three phases:
+ *   [── settled leg A (≥30 s) ──][─ guard (15 s) ─][apex][─ guard (15 s) ─][── settled leg B (≥30 s) ──]
+ *
+ * For each GPS fix as candidate apex: collect before/after settle windows (excluding the guard zone),
+ * require MIN_PTS fixes in each, compute circularMean + circularMAD, reject if MAD > STAB_MAX,
+ * accept if heading delta in [MIN_DELTA, MAX_DELTA].
+ *
+ * De-duplicate: group candidates within MIN_GAP_MS, keep max-delta per group.
+ * Refine position: within the maneuver zone, find the point with the greatest instantaneous
+ * heading rate of change as the map pin.
+ *
+ * No SOG gate: circularMAD stability check handles noise at any speed.
+ * A boat at anchor has effectively random COG (MAD ≈ 90°) and is always rejected.
+ * A real settled tack leg has MAD typically 5–15° and passes.
+ * Mode: CRUISING — conservative (prefers missing a tack over reporting a phantom).
+ * Race mode (shorter windows, wider MAD) is a future backlog item.
+ */
 object TackDetector {
-    private const val HALF_WIN       = 2
-    private const val MIN_DELTA      = 60.0
-    private const val MAX_DELTA      = 140.0
-    private const val STABILITY_MAX  = 30.0
-    private const val MIN_GAP_MS     = 45_000L    // 45 s minimum between tacks
-    private const val START_SKIP_MS  = 120_000L   // skip first 2 min (GPS cold-start noise)
+    private const val T_SETTLE      = 30_000L   // ms — stable heading window required before/after
+    private const val T_MANEUVER    = 30_000L   // ms — guard zone around apex (±15 s each side)
+    private const val STAB_MAX      = 20.0      // °  — max circularMAD in settle windows
+    private const val MIN_DELTA     = 60.0      // °  — minimum heading change to count as tack/jibe
+    private const val MAX_DELTA     = 160.0     // °  — maximum heading change (beyond = U-turn, not a tack)
+    private const val MIN_GAP_MS    = 60_000L   // ms — minimum time between accepted events
+    private const val START_SKIP_MS = 60_000L   // ms — skip first 60 s (cold-start noise)
+    private const val MIN_PTS       = 3         // minimum GPS fixes required in each settle window
+
+    private data class Candidate(
+        val index: Int,
+        val timestampMs: Long,
+        val delta: Double,
+        val cogBefore: Double,
+        val cogAfter: Double
+    )
 
     fun detectTacks(points: List<TrackPoint>): List<TackEvent> {
-        if (points.size < 2 * HALF_WIN + 1) return emptyList()
+        if (points.size < MIN_PTS) return emptyList()
+        val t0 = points.first().timestampMs
 
-        val results = mutableListOf<TackEvent>()
-        var lastTackMs: Long? = null
+        val raw = mutableListOf<Candidate>()
+
+        for (i in points.indices) {
+            val t = points[i].timestampMs
+            if (t - t0 < START_SKIP_MS) continue
+
+            val beforeEnd   = t - T_MANEUVER / 2
+            val beforeStart = beforeEnd - T_SETTLE
+            val before = points.filter { it.timestampMs in beforeStart until beforeEnd }
+            if (before.size < MIN_PTS) continue
 
-        for (i in HALF_WIN until points.size - HALF_WIN) {
-            if (points[i].timestampMs - points.first().timestampMs < START_SKIP_MS) continue
-            if (lastTackMs != null && points[i].timestampMs - lastTackMs < MIN_GAP_MS) continue
+            val afterStart = t + T_MANEUVER / 2
+            val afterEnd   = afterStart + T_SETTLE
+            val after = points.filter { it.timestampMs > afterStart && it.timestampMs <= afterEnd }
+            if (after.size < MIN_PTS) continue
 
-            val spreadBefore = abs(angleDiff(points[i - 2].cogDeg, points[i - 1].cogDeg))
-            val spreadAfter  = abs(angleDiff(points[i + 1].cogDeg, points[i + 2].cogDeg))
-            if (spreadBefore > STABILITY_MAX || spreadAfter > STABILITY_MAX) continue
+            val cogBefore    = circularMean(before.map { it.cogDeg })
+            val spreadBefore = circularMAD(before.map { it.cogDeg }, cogBefore)
+            if (spreadBefore > STAB_MAX) continue
+
+            val cogAfter    = circularMean(after.map { it.cogDeg })
+            val spreadAfter = circularMAD(after.map { it.cogDeg }, cogAfter)
+            if (spreadAfter > STAB_MAX) continue
 
-            val cogBefore = circularMean(points[i - 2].cogDeg, points[i - 1].cogDeg)
-            val cogAfter  = circularMean(points[i + 1].cogDeg, points[i + 2].cogDeg)
             val delta = abs(angleDiff(cogBefore, cogAfter))
+            if (delta < MIN_DELTA || delta > MAX_DELTA) continue
+
+            raw += Candidate(i, t, delta, cogBefore, cogAfter)
+        }
+        if (raw.isEmpty()) return emptyList()
 
-            if (delta in MIN_DELTA..MAX_DELTA) {
-                results += TackEvent(i, points[i].lat, points[i].lon, cogBefore, cogAfter)
-                lastTackMs = points[i].timestampMs
+        // De-duplicate: if consecutive raw candidates are within MIN_GAP_MS of each other, they
+        // belong to the same maneuver. Keep the max-delta candidate per group.
+        // Compare against the PREVIOUS candidate (adjacent comparison) so a long stream of
+        // close candidates from one maneuver stays in a single group regardless of total span.
+        val results = mutableListOf<TackEvent>()
+        var best: Candidate? = null
+        var prevMs = Long.MIN_VALUE / 2
+
+        for (c in raw) {
+            if (best != null && c.timestampMs - prevMs >= MIN_GAP_MS) {
+                results += buildTackEvent(points, best!!)
+                best = c
+            } else {
+                if (best == null || c.delta > best!!.delta) best = c
             }
+            prevMs = c.timestampMs
         }
+        best?.let { results += buildTackEvent(points, it) }
         return results
     }
 
+    private fun buildTackEvent(points: List<TrackPoint>, c: Candidate): TackEvent {
+        // Refine map pin: find max instantaneous heading rate within maneuver zone
+        val maneuvRange = (c.timestampMs - T_MANEUVER / 2)..(c.timestampMs + T_MANEUVER / 2)
+        var bestIdx = c.index
+        var bestRate = 0.0
+        for (i in 1 until points.size) {
+            if (points[i].timestampMs !in maneuvRange) continue
+            val rate = abs(angleDiff(points[i - 1].cogDeg, points[i].cogDeg))
+            if (rate > bestRate) { bestRate = rate; bestIdx = i }
+        }
+        return TackEvent(bestIdx, points[bestIdx].lat, points[bestIdx].lon, c.cogBefore, c.cogAfter)
+    }
+
     internal fun angleDiff(from: Double, to: Double): Double {
         var diff = to - from
-        while (diff > 180)  diff -= 360
+        while (diff >  180) diff -= 360
         while (diff < -180) diff += 360
         return diff
     }
 
-    private fun circularMean(a: Double, b: Double): Double {
-        val half = angleDiff(a, b) / 2.0
-        return ((a + half) % 360.0 + 360.0) % 360.0
+    private fun circularMean(angles: List<Double>): Double {
+        val sinSum = angles.sumOf { sin(Math.toRadians(it)) }
+        val cosSum = angles.sumOf { cos(Math.toRadians(it)) }
+        return ((Math.toDegrees(atan2(sinSum, cosSum)) % 360.0) + 360.0) % 360.0
     }
+
+    private fun circularMAD(angles: List<Double>, mean: Double): Double =
+        angles.map { abs(angleDiff(it, mean)) }.average()
 }