baldav/frontend/js/baro.js

// Barometric altitude from the DIY BLE sensor "BaroBalDav" (ESP32-C3 + BMP280).
// PASSIVE module: it only defines window.BARO. Nothing runs until BARO.start() is called, so with
// no barometer connected the app behaves exactly as before. Activation (start on a "baro" connect,
// plus the getGpsAlt hook) is wired in main.js only when a baro device is in use.
//
// How it works: the Kotlin BLE service writes the latest {pressure_pa, temp_c, ts} to a file; the
// Rust command `ble_get_baro` returns it. We turn pressure into altitude with the hypsometric
// formula using the sensor's own temperature, and anchor the absolute value to the GPS altitude at
// ride start. The sensor is excellent for relative change (~1 m); weather drift of the absolute
// baseline is handled by the GPS anchor (optionally re-anchored slowly).
let BARO = {};
(function () {
  let R = 287.05;     // specific gas constant for dry air, J/(kg*K)
  let G = 9.80665;    // standard gravity, m/s^2

  let state = {
    anchorPa: null,     // reference pressure at the anchor point
    anchorAltM: null,   // absolute altitude (m) at the anchor point, from GPS
    lastPa: null,       // most recent pressure, Pa
    lastTempC: null,    // most recent chip temperature, C (for the hypsometric term)
    lastTs: 0,          // unix seconds of the last reading
    lastAltM: null,     // computed absolute altitude at the last reading
    polling: false,
    timer: null,
  };
  BARO.state = state;

  // Height of a level at pressure `pa` above a level at pressure `refPa`, at air temperature tC.
  // Hypsometric formula: dh = (R*T/g) * ln(refPa/pa). Measured temperature is used instead of a
  // 15 C constant, so a hot or cold day does not bias the climb. Returns metres (positive = higher).
  function deltaH(refPa, pa, tC) {
    let T = (tC == null ? 15 : tC) + 273.15;
    return (R * T / G) * Math.log(refPa / pa);
  }
  BARO.deltaH = deltaH;

  // Pin the barometric altitude to a known absolute altitude (from GPS) at a given pressure.
  // Call once at ride start; may be re-called later to slowly correct weather drift.
  BARO.anchor = function (gpsAltM, pa) {
    if (pa == null) pa = state.lastPa;
    if (gpsAltM == null || pa == null) return false;
    state.anchorAltM = gpsAltM;
    state.anchorPa = pa;
    state.lastAltM = BARO.altitude();
    return true;
  };

  // Absolute altitude now = anchor altitude + barometric rise since the anchor. null until anchored.
  BARO.altitude = function () {
    if (state.anchorPa == null || state.lastPa == null) return null;
    return state.anchorAltM + deltaH(state.anchorPa, state.lastPa, state.lastTempC);
  };

  // Fresh reading within 15 s?
  BARO.isLive = function () {
    return state.lastTs > 0 && (Date.now() / 1000 - state.lastTs) < 15;
  };

  // Override this to provide the current GPS altitude (m) for auto-anchoring; return null if no fix.
  // Default: the altitude of the last recorded GPS point, if a recording is active.
  BARO.getGpsAlt = function () {
    try {
      let pts = window.GPS && GPS.recording && GPS.recording.points;
      if (pts && pts.length) {
        let p = pts[pts.length - 1];
        let a = p.altitude_srtm_m != null ? p.altitude_srtm_m : p.altitude;
        return a != null ? a : null;
      }
    } catch (e) {}
    return null;
  };

  async function tick() {
    let r = null;
    try { r = await window.__TAURI__.core.invoke("ble_get_baro"); } catch (e) {}
    if (r && r.pressure_pa > 0) {
      state.lastPa = r.pressure_pa;
      if (r.temp_c != null) state.lastTempC = r.temp_c;
      state.lastTs = r.timestamp || Math.floor(Date.now() / 1000);
      // auto-anchor on the first good reading, once GPS has an altitude to anchor to
      if (state.anchorPa == null) {
        let g = null;
        try { g = BARO.getGpsAlt(); } catch (e) {}
        if (g != null) BARO.anchor(g, state.lastPa);
      }
      state.lastAltM = BARO.altitude();
    }
  }
  BARO.tick = tick;

  // Begin polling the sensor (~1 Hz). No-op if already running. Call this only when a baro device
  // is connected, so the app does nothing extra when no barometer is in use.
  BARO.start = function () {
    if (state.polling) return;
    state.polling = true;
    let loop = async function () {
      if (!state.polling) return;
      await tick();
      if (state.polling) state.timer = setTimeout(loop, 1000); // 1 s poll interval (a real delay)
    };
    loop();
  };

  BARO.stop = function () {
    state.polling = false;
    if (state.timer) { clearTimeout(state.timer); state.timer = null; }
  };

  // Clear the anchor and readings (e.g. between rides) so the next ride re-anchors fresh.
  BARO.reset = function () {
    state.anchorPa = null; state.anchorAltM = null;
    state.lastPa = null; state.lastTempC = null; state.lastTs = 0; state.lastAltM = null;
  };

  window.BARO = BARO;
})();