Atan2 (two-argument arctangent)

Syntax

Atan2(<y>, <x>)

π Atan2(dy, dx) → bearing_rad (Moves)

Description

Atan2 returns the angle, in radians, of the point (x, y) measured from the positive x axis. Unlike Atn(y / x) it knows the quadrant, since it sees the signs of both coordinates, and it has an answer where x is zero. It is the function for turning a displacement into a heading.

Technical Description

Atan2(y: NUMBER, x: NUMBER) → NUMBER. Returns atan2(y, x) in radians, in (−π, π] (Math.atan2). Note the order: y first, as in SQL's ATAN2(y, x). Atan2(0, 0) is 0. A NULL in either argument returns NULL. PURE, DETERMINISTIC. Floating-point result.

Examples

Heading of each move, in degrees:

π id, Degrees(Atan2(dy, dx)) → heading_deg (Moves)

PROJECT id, Degrees(Atan2(dy, dx)) -> heading_deg (Moves)

Limitations

Returns radians. NUMBER only; NULL in either → NULL out. The argument order is (y, x); swapping them reflects the angle about the diagonal.

Alternatives

Atn(y / x) when x is known to be positive.

See Also

atn, asin, acos, degrees