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Fix altitude unit mismatch in ADSB delay calculation #33

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Fix altitude unit mismatch in ADSB delay calculation #33

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3 changes: 2 additions & 1 deletion api/lib/extrapolation.js
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Expand Up @@ -16,7 +16,8 @@ function extrapolatePosition(aircraft, targetTimestamp) {

const dx = velocityMs * Math.sin(trackRad) * dt;
const dy = velocityMs * Math.cos(trackRad) * dt;
const dz = (aircraft.geom_rate || 0) * 0.00508 * dt;
// geom_rate is ft/min; convert to ft/s to keep altitude in feet
const dz = (aircraft.geom_rate || 0) / 60 * dt;

const latRad = aircraft.lat * Math.PI / 180;
const newLat = aircraft.lat + (dy / 111320);
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8 changes: 4 additions & 4 deletions api/lib/geometry.js
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Expand Up @@ -22,10 +22,10 @@ function calculateBistaticDelay(aircraftPos, rxPos, txPos) {
let dRxAircraft = haversineDistance(rxPos, aircraftPos);
let dTxAircraft = haversineDistance(txPos, aircraftPos);
let dRxTx = haversineDistance(rxPos, txPos);
const altRx = rxPos.alt || 0;
const altTx = txPos.alt || 0;
const altAircraft = aircraftPos.alt || 0;

const altRx = rxPos.alt || 0; // meters (from config)
const altTx = txPos.alt || 0; // meters (from config)
const altAircraft = (aircraftPos.alt || 0) * 0.3048; // feet -> meters

dRxAircraft = Math.sqrt(dRxAircraft**2 + (altAircraft - altRx)**2);
dTxAircraft = Math.sqrt(dTxAircraft**2 + (altAircraft - altTx)**2);
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