ST_Azimuth
Prev  7.12. Measurement Functions  Next

Name

ST_Azimuth — Returns the north-based azimuth of a line between two points.

Synopsis

float ST_Azimuth(geometry origin, geometry target);

float ST_Azimuth(geography origin, geography target);

Description

Returns the azimuth in radians of the target point from the origin point, or NULL if the two points are coincident. The azimuth angle is a positive clockwise angle referenced from the positive Y axis (geometry) or the North meridian (geography): North = 0; Northeast = π/4; East = π/2; Southeast = 3π/4; South = π; Southwest 5π/4; West = 3π/2; Northwest = 7π/4.

For the geography type, the azimuth solution is known as the inverse geodesic problem.

The azimuth is a mathematical concept defined as the angle between a reference vector and a point, with angular units in radians. The result value in radians can be converted to degrees using the PostgreSQL function degrees().

For offsetting lines relative to their direction, use ST_OffsetCurve. For projecting a point by distance and bearing, use ST_Project.

Availability: 1.1.0

Enhanced: 2.0.0 support for geography was introduced.

Enhanced: 2.2.0 measurement on spheroid performed with GeographicLib for improved accuracy and robustness. Requires PROJ >= 4.9.0 to take advantage of the new feature.

Examples

Geometry Azimuth in degrees 

SELECT degrees(ST_Azimuth(ST_Point(25, 45),  ST_Point(75, 100))) AS degA_B,
       degrees(ST_Azimuth(ST_Point(75, 100), ST_Point(25, 45) )) AS degB_A;
      dega_b       |     degb_a
------------------+------------------
42.27368900609371 | 222.27368900609372

Compass direction labels can be computed from the azimuth.

WITH directions(deg) AS (VALUES
  (0), (45), (90), (135), (180), (225), (270), (315)
),
bearings AS (
  SELECT deg,
         degrees(ST_Azimuth(ST_Point(0, 0),
                            ST_MakePoint(sin(radians(deg)),
                                         cos(radians(deg))))) AS azimuth
  FROM directions
)
SELECT deg,
       round(azimuth::numeric, 1) AS azimuth,
       (ARRAY['N', 'NE', 'E', 'SE', 'S', 'SW', 'W', 'NW', 'N'])
         [floor((azimuth + 22.5) / 45)::int + 1] AS direction
FROM bearings
ORDER BY deg;
 deg | azimuth | direction
-----+---------+-----------
   0 |     0.0 | N
  45 |    45.0 | NE
  90 |    90.0 | E
 135 |   135.0 | SE
 180 |   180.0 | S
 225 |   225.0 | SW
 270 |   270.0 | W
 315 |   315.0 | NW

Blue: origin Point(25,45); Green: target Point(75, 100); Yellow: Y axis or North; Red: azimuth angle.

Blue: origin Point(75, 100); Green: target Point(25, 45); Yellow: Y axis or North; Red: azimuth angle.