fix: 🐛 fix calculation of doppler factor

.vscode/tasks.json

@@ -13,6 +13,18 @@
         "color": "terminal.ansiBlue"
       }
     },
+    {
+      "label": "Clean Dist Folder",
+      "command": "npm run clean",
+      "type": "shell",
+      "args": [],
+      "isBackground": true,
+      "problemMatcher": [],
+      "icon": {
+        "id": "trash",
+        "color": "terminal.ansiYellow"
+      }
+    },
     {
       "label": "Test with Jest",
       "command": "npm test",

package.json

@@ -5,7 +5,8 @@
   "module": "dist/main.js",
   "description": "Orbital Object Toolkit. A modern typed replacement for satellite.js including SGP4 propagation, TLE parsing, Sun and Moon calculations, and more.",
   "scripts": {
-    "build": "node ./scripts/cleanup.mjs && npx tsc -p tsconfig.build.json -m esnext",
+    "build": "npm run clean && npx tsc -p tsconfig.build.json -m esnext",
+    "clean": "node ./scripts/cleanup.mjs",
     "lint": "npx eslint src",
     "lint:fix": "npx eslint src --fix",
     "test": "jest",
@@ -50,4 +51,4 @@
     "typescript": "^4.9.5"
   },
   "homepage": "https://github.com/thkruz/ootk-core"
-}
+}

src/utils/constants.ts

@@ -47,6 +47,11 @@ export const ttasec2rad = (asec2rad / 10000.0) as Radians;
  */
 export const masec2rad = (asec2rad / 1000.0) as Radians;
 
+/**
+ * The angular velocity of the Earth in radians per second.
+ */
+export const angularVelocityOfEarth = 7.292115e-5;
+
 /**
  * Astronomical unit in kilometers.
  */

src/utils/functions.ts

@@ -2,7 +2,8 @@
 /* eslint-disable func-style */
 import { AngularDiameterMethod } from '../enums/AngularDiameterMethod';
 import { AngularDistanceMethod } from '../enums/AngularDistanceMethod';
-import { DifferentiableFunction, EciVec3, Radians, SpaceObjectType } from '../types/types';
+import { DifferentiableFunction, EcfVec3, Kilometers, Radians, SpaceObjectType } from '../types/types';
+import { angularVelocityOfEarth, cKmPerSec } from './constants';
 
 /**
  * Calculates the factorial of a given number.
@@ -630,33 +631,24 @@ export const spaceObjType2Str = (spaceObjType: SpaceObjectType): string =>
  * @param velocity - The velocity vector of the source.
  * @returns The calculated Doppler factor.
  */
-export const dopplerFactor = (location: EciVec3, position: EciVec3, velocity: EciVec3): number => {
-  const mfactor = 7.292115e-5;
-  const c = 299792.458; // Speed of light in km/s
-
-  const range = <EciVec3>{
+export const dopplerFactor = (
+  location: EcfVec3<Kilometers>,
+  position: EcfVec3<Kilometers>,
+  velocity: EcfVec3<Kilometers>,
+): number => {
+  const range = <EcfVec3>{
     x: position.x - location.x,
     y: position.y - location.y,
     z: position.z - location.z,
   };
   const distance = Math.sqrt(range.x ** 2 + range.y ** 2 + range.z ** 2);
-
-  const rangeVel = <EciVec3>{
-    x: velocity.x + mfactor * location.y,
-    y: velocity.y - mfactor * location.x,
+  const rangeVel = <EcfVec3>{
+    x: velocity.x + angularVelocityOfEarth * location.y,
+    y: velocity.y - angularVelocityOfEarth * location.x,
     z: velocity.z,
   };
-
   const rangeRate = (range.x * rangeVel.x + range.y * rangeVel.y + range.z * rangeVel.z) / distance;
-  let dopplerFactor = 0;
-
-  if (rangeRate < 0) {
-    dopplerFactor = 1 + (rangeRate / c) * sign(rangeRate);
-  }
-
-  if (rangeRate >= 0) {
-    dopplerFactor = 1 - (rangeRate / c) * sign(rangeRate);
-  }
+  const dopplerFactor = 1 - rangeRate / cKmPerSec;
 
   return dopplerFactor;
 };

test/utils/__snapshots__/utils.test.ts.snap

@@ -0,0 +1,5 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`Doppler factor calculates earth rotation the same as before #1 1`] = `1.000001479636888`;
+
+exports[`Doppler factor calculates earth rotation the same as before #2 1`] = `1`;

test/utils/utils.test.ts

@@ -1,96 +1,116 @@
-import { EciVec3, Kilometers, linearDistance, Vec3 } from '../../src/main';
+import { EcfVec3, Kilometers, linearDistance, RADIUS_OF_EARTH, Vec3 } from '../../src/main';
 import { dopplerFactor, getDayOfYear } from '../../src/utils/functions';
 
-const numDigits = 8;
-
-const earthRadius = 6378.137;
 const sincos45deg = Math.sqrt(2) / 2;
 
 describe('Doppler factor', () => {
-  it('without observer movement', () => {
+  it('works without observer movement and object moving away', () => {
     // North Pole
-    const observerEci = {
+    const observerEcf = {
       x: 0,
       y: 0,
-      z: earthRadius,
-    } as EciVec3;
-    const positionEci = {
+      z: RADIUS_OF_EARTH,
+    } as EcfVec3;
+    const positionEcf = {
       x: 0,
       y: 0,
-      z: earthRadius + 500,
-    } as EciVec3;
-    // Escape velocity
-    const velocityEci = {
-      x: 7.91,
+      z: RADIUS_OF_EARTH + 500,
+    } as EcfVec3;
+    const velocityEcf = {
+      x: 0,
       y: 0,
-      z: 0,
-    } as EciVec3;
-    const dopFactor = dopplerFactor(observerEci, positionEci, velocityEci);
+      z: 1,
+    } as EcfVec3;
+    const dopFactor = dopplerFactor(observerEcf, positionEcf, velocityEcf);
 
-    expect(dopFactor).toBeCloseTo(1, numDigits);
+    expect(dopFactor).toBeLessThan(1);
   });
 
-  it('movement of observer is not affected', () => {
-    const observerEci = {
-      x: earthRadius,
+  it('works without observer movement and object moving towards', () => {
+    // North Pole
+    const observerEcf = {
+      x: 0,
       y: 0,
-      z: 0,
-    } as EciVec3;
-    const positionEci = {
-      x: earthRadius + 500,
+      z: RADIUS_OF_EARTH,
+    } as EcfVec3;
+    const positionEcf = {
+      x: 0,
       y: 0,
-      z: 0,
-    } as EciVec3;
-    const velocityEci = {
+      z: RADIUS_OF_EARTH + 500,
+    } as EcfVec3;
+    const velocityEcf = {
       x: 0,
-      y: 7.91,
-      z: 0,
-    } as EciVec3;
-    const dopFactor = dopplerFactor(observerEci, positionEci, velocityEci);
+      y: 0,
+      z: -1,
+    } as EcfVec3;
+    const dopFactor = dopplerFactor(observerEcf, positionEcf, velocityEcf);
 
-    expect(dopFactor).toBeCloseTo(1, numDigits);
+    expect(dopFactor).toBeGreaterThan(1);
   });
 
-  it('special case', () => {
-    const observerEci = {
-      x: earthRadius,
+  it('calculates earth rotation the same as before #1', () => {
+    const observerEcf = {
+      x: RADIUS_OF_EARTH,
       y: 0,
       z: 0,
-    } as EciVec3;
-    const positionEci = {
-      x: (earthRadius + 500) * sincos45deg, // z*sin(45)
-      y: (earthRadius + 500) * sincos45deg, // z*cos(45)
+    } as EcfVec3;
+    const positionEcf = {
+      x: (RADIUS_OF_EARTH + 500) * sincos45deg, // z*sin(45)
+      y: (RADIUS_OF_EARTH + 500) * sincos45deg, // z*cos(45)
       z: 0,
-    } as EciVec3;
-    const velocityEci = {
-      x: 7.91 * sincos45deg,
-      y: 7.91 * sincos45deg,
+    } as EcfVec3;
+    const velocityEcf = {
+      x: 0,
+      y: 0,
       z: 0,
-    } as EciVec3;
-    const dopFactor = dopplerFactor(observerEci, positionEci, velocityEci);
+    } as EcfVec3;
+    const dopFactor = dopplerFactor(observerEcf, positionEcf, velocityEcf);
 
-    expect(dopFactor).toBeCloseTo(0.9999892152210788, numDigits);
+    expect(dopFactor).toMatchSnapshot();
   });
 
-  test('if negative range rate works', () => {
-    const observerEci = {
-      x: earthRadius,
+  it('works without observer movement and a stationary object', () => {
+    // North Pole
+    const observerEcf = {
+      x: 0,
+      y: 0,
+      z: RADIUS_OF_EARTH,
+    } as EcfVec3;
+    const positionEcf = {
+      x: 0,
+      y: 0,
+      z: RADIUS_OF_EARTH + 500,
+    } as EcfVec3;
+    const velocityEcf = {
+      x: 0,
       y: 0,
       z: 0,
-    } as EciVec3;
-    const positionEci = {
-      x: (earthRadius + 500) * sincos45deg, // z*sin(45)
-      y: (earthRadius + 500) * sincos45deg, // z*cos(45)
+    } as EcfVec3;
+    const dopFactor = dopplerFactor(observerEcf, positionEcf, velocityEcf);
+
+    expect(dopFactor).toEqual(1);
+  });
+
+  it('calculates earth rotation the same as before #2', () => {
+    // North Pole
+    const observerEcf = {
+      x: RADIUS_OF_EARTH,
+      y: 0,
       z: 0,
-    } as EciVec3;
-    const velocityEci = {
-      x: -7.91 * sincos45deg,
-      y: -7.91 * sincos45deg,
+    } as EcfVec3;
+    const positionEcf = {
+      x: RADIUS_OF_EARTH + 500,
+      y: 0,
       z: 0,
-    } as EciVec3;
-    const dopFactor = dopplerFactor(observerEci, positionEci, velocityEci);
+    } as EcfVec3;
+    const velocityEcf = {
+      x: 0,
+      y: 0,
+      z: 1,
+    } as EcfVec3;
+    const dopFactor = dopplerFactor(observerEcf, positionEcf, velocityEcf);
 
-    expect(dopFactor).toBeCloseTo(1.000013747277977, numDigits);
+    expect(dopFactor).toMatchSnapshot();
   });
 });