/**
 * @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 { J2000, Vector3D } from '../main.js';
import { Force } from './Force.js';
/**
 * designed to model the Earth's gravitational field, which is not uniformly distributed due to variations in mass
 * distribution within the Earth and the Earth's shape (it's not a perfect sphere). To accurately model this complex
 * field, the gravity model is expanded into a series of spherical harmonics, characterized by their degree and order.
 *
 * This `degree` parameter is related to the spatial resolution of the gravity model. A higher degree corresponds to a
 * finer resolution, capable of representing smaller-scale variations in the gravity field. The degree essentially
 * denotes how many times the gravitational potential function varies over the surface of the Earth.
 *
 * For each degree, there can be multiple orders ranging from 0 up to the degree. The `order` accounts for the
 * longitudinal variation in the gravity field. Each order within a degree captures different characteristics of the
 * gravity anomalies.
 *
 * `Degree 0` corresponds to the overall, mean gravitational force of the Earth (considered as a point mass).
 *
 * `Degree 1` terms are related to the Earth's center of mass but are usually not used because the center of mass is
 * defined as the origin of the coordinate system.
 *
 * `Degree 2` and higher capture the deviations from this spherical symmetry, such as the flattening at the poles and
 * bulging at the equator (degree 2), and other anomalies at finer scales as the degree increases.
 */
export declare class EarthGravity implements Force {
    degree: number;
    order: number;
    _asphericalFlag: boolean;
    /**
     * Creates a new instance of the EarthGravity class.
     * @param degree The degree of the Earth's gravity field. Must be between 0 and 36.
     * @param order The order of the Earth's gravity field. Must be between 0 and 36.
     */
    constructor(degree: number, order: number);
    _spherical(state: J2000): Vector3D;
    _aspherical(state: J2000): Vector3D;
    acceleration(state: J2000): Vector3D;
}