Suppress map label flicker from GPS jitter

GPS settling produces many tiny position updates that each triggered a
1-second animateCamera(), forcing continuous symbol-collision
recalculation and label fade cycles.

Fix: skip animation entirely (moveCamera) when the new position is
< 3 m from the last one; use a shorter easeCamera(400 ms) for real
movement so the animation window is smaller.

https://claude.ai/code/session_01HXPjBsogsJVRwCiekDGkJX

1 files changed, 20 insertions, 1 deletions

diff --git a/android-app/app/src/main/kotlin/org/terst/nav/ui/MapHandler.kt b/android-app/app/src/main/kotlin/org/terst/nav/ui/MapHandler.kt
index ca146b1..a7d746f 100644
--- a/android-app/app/src/main/kotlin/org/terst/nav/ui/MapHandler.kt
+++ b/android-app/app/src/main/kotlin/org/terst/nav/ui/MapHandler.kt
@@ -26,6 +26,7 @@ import org.terst.nav.data.model.WindArrow
 import org.terst.nav.track.TrackPoint
 import kotlin.math.cos
 import kotlin.math.sin
+import kotlin.math.sqrt
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.asStateFlow
@@ -225,14 +226,32 @@ class MapHandler(private val maplibreMap: MapLibreMap) {
      * Centers the map on the specified location.
      */
     fun centerOnLocation(lat: Double, lon: Double, zoom: Double = 14.0) {
+        val prevLat = lastLat
+        val prevLon = lastLon
         lastLat = lat
         lastLon = lon
         if (!_isFollowing.value) return
+
         val position = CameraPosition.Builder()
             .target(LatLng(lat, lon))
             .zoom(zoom)
             .build()
-        maplibreMap.animateCamera(CameraUpdateFactory.newCameraPosition(position), 1000)
+
+        // Skip animation for tiny GPS jitter (< 3 m) to avoid repeated symbol
+        // collision recalculations that cause labels to flash on/off.
+        val deltaMeters = approximateMeters(prevLat, prevLon, lat, lon)
+        if (deltaMeters < 3.0) {
+            maplibreMap.moveCamera(CameraUpdateFactory.newCameraPosition(position))
+        } else {
+            maplibreMap.easeCamera(CameraUpdateFactory.newCameraPosition(position), 400)
+        }
+    }
+
+    /** Fast flat-earth distance approximation (accurate to ~0.1% within a few km). */
+    private fun approximateMeters(lat1: Double, lon1: Double, lat2: Double, lon2: Double): Double {
+        val dLat = (lat2 - lat1) * 111_320.0
+        val dLon = (lon2 - lon1) * 111_320.0 * cos(Math.toRadians((lat1 + lat2) / 2.0))
+        return sqrt(dLat * dLat + dLon * dLon)
     }
 
     /**