2 files changed, 59 insertions, 0 deletions
diff --git a/test-runner/src/main/kotlin/org/terst/nav/track/TackDetector.kt b/test-runner/src/main/kotlin/org/terst/nav/track/TackDetector.kt
new file mode 100644
index 0000000..b392f67
--- /dev/null
+++ b/test-runner/src/main/kotlin/org/terst/nav/track/TackDetector.kt
@@ -0,0 +1,50 @@
+package org.terst.nav.track
+
+import kotlin.math.abs
+
+object TackDetector {
+    private const val HALF_WIN = 2   // look 2 points before and after
+    private const val MIN_DELTA = 60.0
+    private const val MAX_DELTA = 140.0
+    private const val SKIP_AFTER = 5       // suppress re-detection for this many indices
+    private const val STABILITY_MAX = 30.0  // max internal spread of a before/after pair
+
+    fun detectTacks(points: List<TrackPoint>): List<TackEvent> {
+        if (points.size < 2 * HALF_WIN + 1) return emptyList()
+
+        val results = mutableListOf<TackEvent>()
+        var nextCandidate = 0
+
+        for (i in HALF_WIN until points.size - HALF_WIN) {
+            if (i < nextCandidate) continue
+
+            // Require both "before" and "after" pairs to be internally stable;
+            // if one spans the transition itself, that window is noise.
+            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(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 in MIN_DELTA..MAX_DELTA) {
+                results += TackEvent(i, points[i].lat, points[i].lon, cogBefore, cogAfter)
+                nextCandidate = i + SKIP_AFTER
+            }
+        }
+        return results
+    }
+
+    internal fun angleDiff(from: Double, to: Double): Double {
+        var diff = to - from
+        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
+    }
+}
diff --git a/test-runner/src/main/kotlin/org/terst/nav/track/TackEvent.kt b/test-runner/src/main/kotlin/org/terst/nav/track/TackEvent.kt
new file mode 100644
index 0000000..7c0bf85
--- /dev/null
+++ b/test-runner/src/main/kotlin/org/terst/nav/track/TackEvent.kt
@@ -0,0 +1,9 @@
+package org.terst.nav.track
+
+data class TackEvent(
+    val index: Int,
+    val lat: Double,
+    val lon: Double,
+    val cogBefore: Double,
+    val cogAfter: Double
+)