import type { FnU2 } from "@thi.ng/api";
import type { ReadonlyVec } from "./api.js";
/**
 * Computes direction angle (in radians) of line segment `a` -> `b` in
 * XY plane.
 *
 * @param a -
 * @param b -
 */
export declare const headingSegmentXY: FnU2<ReadonlyVec, number>;
/**
 * Computes direction angle (in radians) of line segment `a` -> `b` in
 * XZ plane.
 *
 * @param a -
 * @param b -
 */
export declare const headingSegmentXZ: FnU2<ReadonlyVec, number>;
/**
 * Computes direction angle (in radians) of line segment `a` -> `b` in
 * ZY plane.
 *
 * @param a -
 * @param b -
 */
export declare const headingSegmentYZ: FnU2<ReadonlyVec, number>;
/**
 * Same as {@link headingSegmentXY}.
 */
export declare const headingSegment: FnU2<ReadonlyVec, number>;
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