ST_Angle
Name
ST_Angle — Returns the angle between 3 points, or between 2 vectors (4 points or 2 lines).
Synopsis
float
ST_Angle
(
geometry
point1
, geometry
point2
, geometry
point3
, geometry
point4
)
;
float
ST_Angle
(
geometry
line1
, geometry
line2
)
;
Description
For 3 points, computes the angle measured clockwise of P1P2P3. If input are 2 lines, get first and last point of the lines as 4 points. For 4 points,compute the angle measured clockwise of P1P2,P3P4. Results are always positive, between 0 and 2*Pi radians. Uses azimuth of pairs or points.
ST_Angle(P1,P2,P3) = ST_Angle(P2,P1,P2,P3)
Result is in radian and can be converted to degrees using a built-in PostgreSQL function degrees(), as shown in the example.
Availability: 2.5.0
Examples
Geometry Azimuth in degrees
WITH rand AS ( SELECT s, random() * 2 * PI() AS rad1 , random() * 2 * PI() AS rad2 FROM generate_series(1,2,2) AS s ) , points AS ( SELECT s, rad1,rad2, ST_MakePoint(cos1+s,sin1+s) as p1, ST_MakePoint(s,s) AS p2, ST_MakePoint(cos2+s,sin2+s) as p3 FROM rand ,cos(rad1) cos1, sin(rad1) sin1 ,cos(rad2) cos2, sin(rad2) sin2 ) SELECT s, ST_AsText(ST_SnapToGrid(ST_MakeLine(ARRAY[p1,p2,p3]),0.001)) AS line , degrees(ST_Angle(p1,p2,p3)) as computed_angle , round(degrees(2*PI()-rad2 -2*PI()+rad1+2*PI()))::int%360 AS reference , round(degrees(2*PI()-rad2 -2*PI()+rad1+2*PI()))::int%360 AS reference FROM points ; 1 | line | computed_angle | reference ------------------+------------------ 1 | LINESTRING(1.511 1.86,1 1,0.896 0.005) | 155.27033848688 | 155