ST_Angle — Returns the angle between two vectors defined by 3 or 4 points, or 2 lines.
float ST_Angle(geometry point1, geometry point2, geometry point3, geometry point4);
float ST_Angle(geometry line1, geometry line2);
Computes the clockwise angle between two vectors.
Variant 1: computes the angle enclosed by the points P1-P2-P3. If a 4th point provided computes the angle points P1-P2 and P3-P4
Variant 2: computes the angle between two vectors S1-E1 and S2-E2, defined by the start and end points of the input lines
The result is a positive angle between 0 and 2π radians.
The radian result can be converted to degrees using the PostgreSQL function degrees().
Note that ST_Angle(P1,P2,P3) = ST_Angle(P2,P1,P2,P3).
Availability: 2.5.0
Angle between three points
SELECT degrees( ST_Angle('POINT(0 0)', 'POINT(10 10)', 'POINT(20 0)') );
degrees
---------
270
Angle between vectors defined by four points
SELECT degrees( ST_Angle('POINT (10 10)', 'POINT (0 0)', 'POINT(90 90)', 'POINT (100 80)') );
degrees
-------------------
269.9999999999999
Angle between vectors defined by the start and end points of lines
SELECT degrees( ST_Angle('LINESTRING(0 0, 0.3 0.7, 1 1)', 'LINESTRING(0 0, 0.2 0.5, 1 0)') );
degrees
--------------
45