/** Keep a share between 0 and 1. Anything that is not a number is 0. */
export declare const clampFollow: (value: number) => number;
/**
 * The sidereal angle the camera uses, in degrees. `anchor` is the Earth's turn when the camera was set, `spin` is the turn now.
 *
 * @param anchor - The Earth's turn, in degrees, remembered for the space camera.
 * @param spin - The Earth's turn now, in degrees.
 * @param follow - 0 holds the stars, 1 turns with the Earth.
 * @returns The angle added to the place the camera looks at.
 */
export declare const followSpin: (anchor: number, spin: number, follow: number) => number;
/**
 * The longitude, in degrees, under the middle of the view. The same place before and after a change of `follow`.
 *
 * @param anchor - The Earth's turn remembered for the camera.
 * @param spin - The Earth's turn now.
 * @param follow - The share of that turn the camera takes.
 * @param centreLon - The home longitude.
 * @param yaw - The view's yaw, in degrees.
 * @returns Longitude under the middle, in degrees.
 */
export declare const groundLongitude: (anchor: number, spin: number, follow: number, centreLon: number, yaw: number) => number;
/**
 * Move the camera's anchor, and the yaw when the share becomes 1, so the longitude under the middle stays put.
 *
 * @param anchor - The anchor before the change.
 * @param spin - The Earth's turn now.
 * @param from - The share before the change.
 * @param to - The share after the change.
 * @param yaw - The view's yaw before the change.
 * @returns The anchor and yaw to use with `to`.
 */
export declare function retargetFollow(anchor: number, spin: number, from: number, to: number, yaw: number): {
    anchor: number;
    yaw: number;
};