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/lib/src/feature/recording/bloc/recording_bloc.dart

@@ -110,7 +110,7 @@ class RecordingBloc(
   final Stream<void> _ticks =
       ticks ?? Stream<void>.periodic(const Duration(seconds: 1));
 
-  static final _sample = RegExp('^[phs] ');
+  static final _sample = RegExp('^[phsb] ');
 
   /// The lines the recorder wrote so far.
   final _lines = StringBuffer();

apps/train/halkyon_train_flutter/lib/src/feature/recording/data/recorded_workout.dart

@@ -228,6 +228,7 @@ List<SeriesChunk> seriesOf(Recording recording) {
   final rates = recording.heartRates;
   final pauses = recording.pauses;
   final rowing = recording.rowing;
+  final pressures = recording.pressures;
   return [
     ...chunksOf(
       SeriesKind.position,
@@ -275,6 +276,14 @@ List<SeriesChunk> seriesOf(Recording recording) {
         },
       ),
     },
+    ...chunksOf(
+      SeriesKind.pressure,
+      start: start,
+      times: times(pressures.map((pressure) => pressure.time)),
+      columns: {
+        'dpa': [for (final pressure in pressures) pressure.decipascals],
+      },
+    ),
     ...chunksOf(
       SeriesKind.pauses,
       start: start,

apps/train/halkyon_train_flutter/lib/src/feature/recording/data/recording_file.dart

@@ -23,6 +23,7 @@ const recordingFileMagic = 'halkyon-train-recording';
 /// p <time> <lat e7> <lon e7> <accuracy cm> <altitude cm or ->
 /// h <time> <bpm>
 /// s <time>
+/// b <time> <the air's pressure, in tenths of a pascal>
 /// pause <time> auto|manual
 /// resume <time> auto|manual
 /// strap <time> connecting|connected|lost
@@ -66,6 +67,7 @@ Recording? readRecording(String text) {
     final heartRates = <HeartRate>[];
     final steps = <DateTime>[];
     final pauses = <PauseMark>[];
+    final pressures = <Pressure>[];
     final straps = <LinkMark>[];
     final loops = <LinkMark>[];
     final rowing = <RowingSample>[];
@@ -153,6 +155,10 @@ Recording? readRecording(String text) {
           }
         case ['s', _]:
           steps.add(time);
+        case ['b', _, final decipascals]:
+          if (int.tryParse(decipascals) case final decipascals?) {
+            pressures.add(Pressure(time: time, decipascals: decipascals));
+          }
         case [final mark, _, final by]
             when (mark == 'pause' || mark == 'resume') &&
                 (by == 'auto' || by == 'manual'):
@@ -189,6 +195,7 @@ Recording? readRecording(String text) {
       heartRates: heartRates,
       steps: steps,
       pauses: pauses,
+      pressures: pressures,
       straps: straps,
       loops: loops,
       rowing: rowing,

apps/train/halkyon_train_flutter/lib/src/feature/recording/model/recording.dart

@@ -31,6 +31,16 @@ final class const HeartRate({
   List<Object?> get props => [time, bpm];
 }
 
+/// The air's pressure at [time], in tenths of a pascal, from the phone's
+/// barometer (D49): averaged over the few seconds before it.
+final class const Pressure({
+  required final DateTime time,
+  required final int decipascals,
+}) with Equatable {
+  @override
+  List<Object?> get props => [time, decipascals];
+}
+
 /// A frame of the rower's (D28): its stroke rate, and its strokes and metres
 /// since the recording's first frame; each null where the frame lacks it.
 final class const RowingSample({
@@ -138,6 +148,9 @@ final class const Recording({
   final List<DateTime> steps = const [],
   final List<PauseMark> pauses = const [],
 
+  /// The barometer's readings, where the phone has one (D49).
+  final List<Pressure> pressures = const [],
+
   /// The strap's states, where it was recorded with one (D27).
   final List<LinkMark> straps = const [],
 
@@ -174,6 +187,7 @@ final class const Recording({
     ...steps,
     for (final mark in pauses) mark.time,
     for (final sample in rowing) sample.time,
+    for (final pressure in pressures) pressure.time,
   ].reduce((a, b) => b.isAfter(a) ? b : a);
 
   @override
@@ -184,6 +198,7 @@ final class const Recording({
     heartRates,
     steps,
     pauses,
+    pressures,
     straps,
     loops,
     rowing,

apps/train/halkyon_train_flutter/lib/src/feature/workout/data/workout_analysis.dart

@@ -64,8 +64,8 @@ final class const WorkoutAnalysis({
   /// Per kilometre on foot, per 5 km cycling, per 500 m on the rower.
   required final List<Split> splits,
 
-  /// The climbs above [climbThresholdMetres], added up; null without
-  /// altitudes.
+  /// The climbs above [climbThresholdMetres] (above [barometerClimbMetres]
+  /// by the barometer, D49), added up; null without altitudes.
   required final int? elevationGainMetres,
 
   /// The pace (seconds a kilometre takes) on foot, the speed (km/h)
@@ -110,7 +110,7 @@ int splitMetresOf(Activity activity) => switch (activity) {
 
 /// [content] and its [series] read for its page.
 WorkoutAnalysis analyse(WorkoutContent content, List<SeriesChunk> series) {
-  final recording = recordingOf(content, series);
+  final recording = withBarometer(recordingOf(content, series));
   final points = _moving(recording);
   final rowed = recording.rowing.isNotEmpty;
   // How far it had gone over its moving time: by the track, or the rower.
@@ -157,7 +157,10 @@ WorkoutAnalysis analyse(WorkoutContent content, List<SeriesChunk> series) {
       strokeRates: strokeRates,
       watts: watts,
     ),
-    elevationGainMetres: _gain(points),
+    elevationGainMetres: _gain(
+      points,
+      recording.pressures.isEmpty ? climbThresholdMetres : barometerClimbMetres,
+    ),
     chart: _chart(
       progress,
       per: switch (content.activity) {
@@ -420,6 +423,7 @@ Recording recordingOf(WorkoutContent content, List<SeriesChunk> series) {
   final pauses = <PauseMark>[];
   final heartRates = <HeartRate>[];
   final rowing = <RowingSample>[];
+  final pressures = <Pressure>[];
   for (final chunk in series) {
     final times = chunk.absoluteTimes;
     final columns = chunk.columns;
@@ -474,6 +478,12 @@ Recording recordingOf(WorkoutContent content, List<SeriesChunk> series) {
             ),
           );
         }
+      case SeriesKind.pressure:
+        for (var i = 0; i < times.length; i++) {
+          if (columns['dpa']?[i] case final decipascals?) {
+            pressures.add(Pressure(time: times[i], decipascals: decipascals));
+          }
+        }
       case SeriesKind.cadence:
       // A recording holds its steps, which a cadence can't give back; the
       // music reads it from the series (`cadenceModelOf`).
@@ -483,6 +493,7 @@ Recording recordingOf(WorkoutContent content, List<SeriesChunk> series) {
   fixes.sort((a, b) => a.time.compareTo(b.time));
   pauses.sort((a, b) => a.time.compareTo(b.time));
   heartRates.sort((a, b) => a.time.compareTo(b.time));
+  pressures.sort((a, b) => a.time.compareTo(b.time));
   return Recording(
     activity: content.activity,
     startedAt: content.startedAt,
@@ -490,10 +501,96 @@ Recording recordingOf(WorkoutContent content, List<SeriesChunk> series) {
     pauses: pauses,
     heartRates: heartRates,
     rowing: rowing,
+    pressures: pressures,
     endedAt: content.endedAt,
   );
 }
 
+/// The climb, in metres, the barometer's elevation must make before it
+/// counts (D49): its noise is a fraction of a metre.
+const barometerClimbMetres = 1;
+
+/// [recording] with its fixes' altitudes from the barometer (D49), where it
+/// kept the air's pressure: each fix's height by the standard atmosphere at
+/// the pressure then (between two readings, as it went; a minute from the
+/// nearest at most), moved by the median of the GPS altitudes less those,
+/// so that its changes are the barometer's and its level GPS's on the
+/// whole; as it is without readings.
+Recording withBarometer(Recording recording) {
+  final pressures = recording.pressures;
+  if (pressures.isEmpty || recording.fixes.isEmpty) {
+    return recording;
+  }
+  double height(double decipascals) =>
+      44330 * (1 - pow(decipascals / 1013250, 1 / 5.255).toDouble());
+  var next = 0;
+  double? pressureAt(DateTime time) {
+    while (next < pressures.length && pressures[next].time.isBefore(time)) {
+      next++;
+    }
+    final after = next < pressures.length ? pressures[next] : null;
+    final before = next > 0 ? pressures[next - 1] : null;
+    if (before != null && after != null) {
+      final span = after.time.difference(before.time).inMilliseconds;
+      final share = span == 0
+          ? 0
+          : time.difference(before.time).inMilliseconds / span;
+      return before.decipascals +
+          (after.decipascals - before.decipascals) * share.toDouble();
+    }
+    final nearest = before ?? after!;
+    return time.difference(nearest.time).abs() <= const Duration(minutes: 1)
+        ? nearest.decipascals.toDouble()
+        : null;
+  }
+
+  final heights = [
+    for (final fix in recording.fixes)
+      switch (pressureAt(fix.time)) {
+        final decipascals? => height(decipascals),
+        null => null,
+      },
+  ];
+  final offsets = [
+    for (final (i, fix) in recording.fixes.indexed)
+      if ((fix.altitudeCm, heights[i]) case (final cm?, final height?)
+          when fix.accuracyCm <= maxAccuracyCm)
+        cm / 100 - height,
+  ]..sort();
+  final offset = offsets.isEmpty ? 0.0 : offsets[offsets.length ~/ 2];
+  return Recording(
+    activity: recording.activity,
+    startedAt: recording.startedAt,
+    fixes: [
+      for (final (i, fix) in recording.fixes.indexed)
+        Fix(
+          time: fix.time,
+          latE7: fix.latE7,
+          lonE7: fix.lonE7,
+          accuracyCm: fix.accuracyCm,
+          altitudeCm: switch (heights[i]) {
+            final height? => ((height + offset) * 100).round(),
+            null => fix.altitudeCm,
+          },
+        ),
+    ],
+    heartRates: recording.heartRates,
+    steps: recording.steps,
+    pauses: recording.pauses,
+    pressures: pressures,
+    straps: recording.straps,
+    loops: recording.loops,
+    rowing: recording.rowing,
+    rowers: recording.rowers,
+    plan: recording.plan,
+    planSteps: recording.planSteps,
+    planMaxHeartRate: recording.planMaxHeartRate,
+    route: recording.route,
+    guidance: recording.guidance,
+    endedAt: recording.endedAt,
+  );
+}
+
 /// A fix that counts, with how far and how long it had moved by then, and
 /// whether a pause came before it since the fix before.
 typedef _Point = ({Fix fix, double metres, Duration moving, bool afterPause});
@@ -611,7 +708,7 @@ List<Split> _splits(
   }
 }
 
-int? _gain(List<_Point> points) {
+int? _gain(List<_Point> points, num threshold) {
   final altitudes = [
     for (final p in points)
       if (p.fix.altitudeCm case final cm?) cm / 100,
@@ -622,10 +719,10 @@ int? _gain(List<_Point> points) {
   var reference = altitudes.first;
   var gain = 0.0;
   for (final altitude in altitudes.skip(1)) {
-    if (altitude > reference + climbThresholdMetres) {
+    if (altitude > reference + threshold) {
       gain += altitude - reference;
       reference = altitude;
-    } else if (altitude < reference - climbThresholdMetres) {
+    } else if (altitude < reference - threshold) {
       reference = altitude;
     }
   }

apps/train/halkyon_train_flutter/lib/src/feature/workout/data/workout_export.dart

@@ -65,7 +65,7 @@ final class const ExportTrack({
 /// last 5 s, the cadence of the window it fell in (on foot, as strides) and
 /// the rower's stroke rate and watts.
 ExportTrack exportTrackOf(WorkoutContent content, List<SeriesChunk> series) {
-  final recording = recordingOf(content, series);
+  final recording = withBarometer(recordingOf(content, series));
   final heart = _Latest(
     [for (final rate in recording.heartRates) (rate.time, rate.bpm)],
     const Duration(seconds: 5),

apps/train/halkyon_train_flutter/lib/src/feature/workout/model/series_chunk.dart

@@ -21,6 +21,10 @@ enum SeriesKind() {
   /// The steps' cadence (D48): `spm`, the steps a minute over the 10 s
   /// before each sample, taken while moving.
   cadence,
+
+  /// The air's pressure from the barometer (D49): `dpa`, in tenths of a
+  /// pascal, every few seconds.
+  pressure,
 }
 
 /// How long a chunk runs at most: a 3-hour ride is 18 chunks of a few KB