/**
 * The elevation, in degrees, above which a satellite counts as seen from the ground: the footprint is the circle from which it stands at least this high.
 *
 * @example
 * ```ts
 * import { BEAM_ELEVATION } from "@johnmorrisdotca/chikyu-earth/space";
 *
 * console.log(BEAM_ELEVATION);
 * ```
 */
export declare const BEAM_ELEVATION = 25;
/**
 * The angle at the Earth's centre between the point below a satellite and the edge of its footprint, in radians: the ground circle from which the satellite is above `elevation`.
 * It is `acos(R cos(e) / (R + h)) - e` for the Earth's radius R, the height h and the elevation e. A satellite on or under the ground, or an elevation of 90 degrees or more, has none.
 *
 * @param heightKm - The satellite's height above the ground, in kilometres.
 * @param elevation - The least elevation, in degrees. 25 when left out.
 * @returns The angle, in radians, from 0 up to a quarter of a turn.
 * @example
 * ```ts
 * import { footprintAngle } from "@johnmorrisdotca/chikyu-earth/space";
 *
 * console.log((footprintAngle(420) * 180) / Math.PI);
 * ```
 */
export declare function footprintAngle(heightKm: number, elevation?: number): number;
/**
 * The radius of a satellite's footprint along the ground, in kilometres: the Earth's radius times {@link footprintAngle}.
 *
 * @param heightKm - The satellite's height above the ground, in kilometres.
 * @param elevation - The least elevation, in degrees. 25 when left out.
 * @returns The radius in kilometres.
 * @example
 * ```ts
 * import { footprintKm } from "@johnmorrisdotca/chikyu-earth/space";
 *
 * console.log(Math.round(footprintKm(550)));
 * ```
 */
export declare const footprintKm: (heightKm: number, elevation?: number) => number;
/**
 * The spot cells inside a footprint: where each one's middle is, and how large they are, in the footprint's own units (the footprint's radius is 1).
 *
 * @example
 * ```ts no-run
 * import type { BeamCells } from "@johnmorrisdotca/chikyu-earth/space";
 *
 * const none: BeamCells = { lattice: [], pitch: 0, radius: 0 };
 * console.log(none.lattice.length);
 * ```
 */
export interface BeamCells {
    /** Each cell's middle on the lattice, in units of the distance between neighbours (the hexagonal pack: one at the middle, then rings of six, twelve, eighteen). */
    lattice: number[][];
    /** The distance between neighbouring cells as a share of the footprint's radius. */
    pitch: number;
    /** A cell's radius as a share of the footprint's radius. */
    radius: number;
}
/**
 * The spot cells of a footprint: `count` circles in a hexagonal pack (the middle one, then the nearest to it), drawn to fit inside the footprint, or at most `cellKm` in radius when that is smaller.
 * It is an illustration of a satellite that serves the ground in cells; it is not the pattern of any operator's beam plan.
 *
 * @param count - How many cells (0 for none; the most is 91, six rings).
 * @param radiusKm - The footprint's radius along the ground, in kilometres.
 * @param cellKm - A cell's radius in kilometres, when the page wants it smaller than the fit; 0 for the fit.
 * @returns The cells.
 * @example
 * ```ts
 * import { beamCells } from "@johnmorrisdotca/chikyu-earth/space";
 *
 * console.log(beamCells(19, 2200, 0).lattice.length);
 * ```
 */
export declare function beamCells(count: number, radiusKm: number, cellKm?: number): BeamCells;
/**
 * The attributes the beam reads: `beam`, `beam-elevation`, `beam-cells`, `beam-cell-size`, `beam-color` and `beam-strength`.
 *
 * @example
 * ```ts
 * import { BEAM_ATTRIBUTES } from "@johnmorrisdotca/chikyu-earth/space";
 *
 * console.log(BEAM_ATTRIBUTES.join(" "));
 * ```
 */
export declare const BEAM_ATTRIBUTES: readonly ["beam", "beam-elevation", "beam-cells", "beam-cell-size", "beam-color", "beam-strength"];
/**
 * What the attributes say: whether the beam is on, and its options.
 *
 * @example
 * ```ts no-run
 * import type { BeamOptions } from "@johnmorrisdotca/chikyu-earth/space";
 *
 * const options: BeamOptions = { on: true, elevation: 25, cells: 19, cellSize: 0, colour: "#8fd1ff", strength: 0.6 };
 * console.log(options.cells);
 * ```
 */
export interface BeamOptions {
    on: boolean;
    elevation: number;
    cells: number;
    cellSize: number;
    colour: string;
    strength: number;
}
/**
 * The beam's colour when the page names none: a pale blue that reads on the day side and the night side.
 *
 * @example
 * ```ts
 * import { BEAM_COLOUR } from "@johnmorrisdotca/chikyu-earth/space";
 *
 * console.log(BEAM_COLOUR);
 * ```
 */
export declare const BEAM_COLOUR = "#8fd1ff";
/**
 * What the beam's attributes say. `beam` is off when it is missing, `off` or `false`; a bare attribute, `selected` or `on` switches it on for the chosen satellite. The strength is from 0 to 1 (0.6 when left out),
 * the elevation from 0 to 80 degrees (25), the cells from 0 to 91 (none) and the cell size in kilometres (0 for the fit).
 *
 * @param get - Reads an attribute by name, `null` when it is missing.
 * @returns The options.
 * @example
 * ```ts
 * import { readBeam } from "@johnmorrisdotca/chikyu-earth/space";
 *
 * const read = readBeam((name) => ({ beam: "selected", "beam-cells": "19" })[name] ?? null);
 * console.log(read.on, read.cells);
 * ```
 */
export declare function readBeam(get: (name: string) => string | null): BeamOptions;