ootk/src/observation/ObservationUtils.ts

Orbital Object Toolkit including Multiple Propagators, Initial Orbit Determination, and Maneuver Calculations.

/**
 * @author @thkruz Theodore Kruczek
 * @license AGPL-3.0-or-later
 * @copyright (c) 2025 Kruczek Labs LLC
 *
 * Orbital Object ToolKit is free software: you can redistribute it and/or modify it under the
 * terms of the GNU Affero General Public License as published by the Free Software
 * Foundation, either version 3 of the License, or (at your option) any later version.
 *
 * Orbital Object ToolKit is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
 * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License along with
 * Orbital Object ToolKit. If not, see <http://www.gnu.org/licenses/>.
 */

import { Radians, Kilometers, Vector3D, RadiansPerSecond, KilometersPerSecond, Matrix } from '../main.js';

export const radecToPosition = (ra: Radians, dec: Radians, r: Kilometers): Vector3D<Kilometers> => {
  const ca = Math.cos(ra);
  const sa = Math.sin(ra);
  const cd = Math.cos(dec);
  const sd = Math.sin(dec);

  return new Vector3D(r * cd * ca as Kilometers, r * cd * sa as Kilometers, r * sd as Kilometers);
};

export const radecToVelocity = (
  ra: Radians,
  dec: Radians,
  r: Kilometers,
  raDot: RadiansPerSecond,
  decDot: RadiansPerSecond,
  rDot: KilometersPerSecond,
): Vector3D<KilometersPerSecond> => {
  const ca = Math.cos(ra);
  const sa = Math.sin(ra);
  const cd = Math.cos(dec);
  const sd = Math.sin(dec);

  return new Vector3D(
    rDot * cd * ca - r * sd * ca * decDot - r * cd * sa * raDot as KilometersPerSecond,
    rDot * cd * sa - r * sd * sa * decDot + r * cd * ca * raDot as KilometersPerSecond,
    rDot * sd + r * cd * decDot as KilometersPerSecond,
  );
};

export const normalizeAngle = (a: number, b: number): number => {
  const x = a - b;

  return Math.atan2(Math.sin(x), Math.cos(x));
};

export const observationDerivative = (xh: number, xl: number, step: number, isAngle = false): number =>
  (isAngle ? normalizeAngle(xh, xl) : xh - xl) / step;

export const observationNoiseFromSigmas = (sigmas: number[]): Matrix => {
  const n = sigmas.length;
  const result = Array.from({ length: n }, () => Array(n).fill(0.0));

  for (let i = 0; i < n; i++) {
    const s = sigmas[i];

    result[i][i] = 1 / (s * s);
  }

  return new Matrix(result);
};