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Fix Error in calculating the Doppler Factor #128

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Fix Error in calculating the Doppler Factor #128

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b232b8b
build: :arrow_up: update jest
thkruz Jan 14, 2024
7ba4c6b
fix: :bug: fix to doppler calculation error
thkruz Jan 14, 2024
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3 changes: 1 addition & 2 deletions package.json
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Original file line number Diff line number Diff line change
Expand Up @@ -40,7 +40,6 @@
"bugs": {
"url": "https://github.com/shashwatak/satellite-js/issues"
},
"dependencies": {},
"devDependencies": {
"@babel/cli": "^7.20.7",
"@babel/core": "^7.20.12",
Expand All @@ -60,7 +59,7 @@
"eslint-config-airbnb-base": "^15.0.0",
"eslint-plugin-import": "^2.26.0",
"glob": "^8.0.3",
"jest": "^29.3.1",
"jest": "^29.7.0",
"prepend-file": "^2.0.1",
"raise-version": "^0.5.0",
"rimraf": "^3.0.2",
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16 changes: 8 additions & 8 deletions src/dopplerFactor.js
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
export default function dopplerFactor(location, position, velocity) {
const mfactor = 7.292115E-5;
const earthRotation = 7.292115E-5;
const c = 299792.458; // Speed of light in km/s

const range = {
Expand All @@ -10,16 +10,16 @@ export default function dopplerFactor(location, position, velocity) {
range.w = Math.sqrt(range.x ** 2 + range.y ** 2 + range.z ** 2);

const rangeVel = {
x: velocity.x + mfactor * location.y,
y: velocity.y - mfactor * location.x,
x: velocity.x + earthRotation * location.y,
y: velocity.y - earthRotation * location.x,
z: velocity.z,
};

function sign(value) {
return value >= 0 ? 1 : -1;
}

const rangeRate = (range.x * rangeVel.x + range.y * rangeVel.y + range.z * rangeVel.z) / range.w;

return (1 + (rangeRate / c) * sign(rangeRate));
// Negative range rate means the satellite is moving towards the observer and
// its frequency is shifted higher because 1 minus a negative range rate is
// positive. If the range rate is positive, the satellite is moving away from
// the observer and its frequency is shifted lower.
return 1 - rangeRate / c;
}
3 changes: 2 additions & 1 deletion test/dopplerFactor.test.js
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Expand Up @@ -48,6 +48,7 @@ describe('Doppler factor', () => {
expect(dopFactor).toBeCloseTo(1, numDigits);
});

// Object moving away from observer
it('special case', () => {
const observerEcf = {
x: earthRadius,
Expand All @@ -65,7 +66,7 @@ describe('Doppler factor', () => {
z: 0,
};
const dopFactor = dopplerFactor(observerEcf, positionEcf, velocityEcf);
expect(dopFactor).toBeCloseTo(1.0000107847789212, numDigits);
expect(dopFactor).toBeCloseTo(0.9999892152210788, numDigits);
});

it('calculated from a negative range rate', () => {
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