feat(train): elevation from the barometer, its pressure kept raw (ADR 0030, D49)

11c: where a recording has GPS and the phone a barometer, the service
averages its readings over 5 s into the file's `b` lines and the
workout's new `pressure` series (tenths of a pascal). The page, Health
Connect's totals and the exported files take the fixes' altitudes from
it: the standard atmosphere's height at the pressure, levelled by the
median of GPS's altitudes less those; climbs count above 1 m. Workouts
recorded before keep GPS's altitudes; an older app skips the series.

Not tried on a phone yet.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

apps/train/halkyon_train_flutter/android/app/src/main/kotlin/app/halkyon/train/PressureAverage.kt

@@ -0,0 +1,26 @@
+package app.halkyon.train
+
+import kotlin.math.roundToLong
+
+/**
+ * The barometer's readings (hPa, several a second) averaged over [windowMs] (ADR 0030, D49):
+ * each window's mean, in tenths of a pascal, as the reading that closes it comes.
+ */
+class PressureAverage(private val windowMs: Long = 5_000) {
+  private var from: Long? = null
+  private var sum = 0.0
+  private var count = 0
+
+  /** Takes the reading [hPa] at [at]; the window's mean where it closed. */
+  fun add(at: Long, hPa: Float): Long? {
+    val start = from ?: at.also { from = it }
+    sum += hPa
+    count++
+    if (at - start < windowMs) return null
+    val mean = (sum / count * 1_000).roundToLong()
+    from = null
+    sum = 0.0
+    count = 0
+    return mean
+  }
+}

apps/train/halkyon_train_flutter/android/app/src/main/kotlin/app/halkyon/train/RecorderService.kt

@@ -39,7 +39,7 @@ import org.json.JSONObject
 // The recording's side of the system (ADR 0030, D13, D16, D18, D19): a
 // foreground service, started from the open app, that takes GPS fixes from
 // Android's LocationManager (no Play services) and steps from the step
-// detector, reads the heart-rate strap and the rower where the person chose
+// detector and the air's pressure from the barometer (D49), reads the heart-rate strap and the rower where the person chose
 // them (D26 to D28), and the Loop's heart rate where no strap gives one (D41),
 // pauses by itself, and appends each sample as a line to the
 // recording file, flushed every few seconds, so a recording survives the app
@@ -174,6 +174,9 @@ class RecorderService : Service(), LocationListener, SensorEventListener {
   private var usualCadence = 165
   private var lastMusicAt = 0L
 
+  /** The barometer's readings, averaged every 5 s (D49). */
+  private val pressure = PressureAverage()
+
   /** What tells each distance passed (D49), and its words. */
   private var announcer: Announcer? = null
   private var announceWords: AnnounceWords? = null
@@ -272,6 +275,15 @@ class RecorderService : Service(), LocationListener, SensorEventListener {
       getSystemService(LocationManager::class.java)
         .requestLocationUpdates(LocationManager.GPS_PROVIDER, 1_000L, 0f, this, Looper.getMainLooper())
     }
+    // The air's pressure where the phone has a barometer: the elevation
+    // GPS gives poorly (D49).
+    if (located) {
+      getSystemService(SensorManager::class.java).let { sensors ->
+        sensors.getDefaultSensor(Sensor.TYPE_PRESSURE)?.let {
+          sensors.registerListener(this, it, SensorManager.SENSOR_DELAY_NORMAL)
+        }
+      }
+    }
     if (stepping) {
       getSystemService(SensorManager::class.java).let { sensors ->
         sensors.getDefaultSensor(Sensor.TYPE_STEP_DETECTOR)?.let {
@@ -595,6 +607,11 @@ class RecorderService : Service(), LocationListener, SensorEventListener {
   }
 
   override fun onSensorChanged(event: SensorEvent) {
+    if (event.sensor.type == Sensor.TYPE_PRESSURE) {
+      val at = wallTime(event.timestamp)
+      pressure.add(at, event.values[0])?.let { decipascals -> write("b $at $decipascals") }
+      return
+    }
     if (event.sensor.type != Sensor.TYPE_STEP_DETECTOR) return
     val at = wallTime(event.timestamp)
     write("s $at")

apps/train/halkyon_train_flutter/android/app/src/test/kotlin/app/halkyon/train/PressureAverageTest.kt

@@ -0,0 +1,18 @@
+package app.halkyon.train
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNull
+import org.junit.Test
+
+/** The barometer's readings averaged every 5 s (ADR 0030, D49). */
+class PressureAverageTest {
+  @Test
+  fun `a window's readings come out as their mean in tenths of a pascal, once it closes`() {
+    val average = PressureAverage()
+    assertNull(average.add(0, 1000.0f))
+    assertNull(average.add(2_000, 1000.2f))
+    assertEquals(1_000_100L, average.add(5_000, 1000.1f))
+    assertNull(average.add(5_200, 990.0f))
+    assertEquals(990_000L, average.add(10_200, 990.0f))
+  }
+}