Calculate the rotation angle of a trajectory with the ST_Angle function - PolarDB

Calculates the rotation angle of a trajectory at each intermediate point and returns the results as an array of double precision values.

Syntax

double precision[] ST_Angle(trajectory traj, boolean hasdirection default false);

Parameter	Description
`traj`	The trajectory object.
`hasdirection`	Specifies whether to include rotation direction in the result. When set to `true`, counterclockwise rotations return negative values. Default value: `false`.

For a trajectory with *n* points, ST_Angle evaluates each of the *n* − 2 intermediate points and returns the rotation angle at that point.

If the trajectory moves in a straight line at an intermediate point, the rotation angle is 0.
If the trajectory does not move at an intermediate point, the rotation angle is NaN.

The following examples use the same nine-point LINESTRING. The trajectory has 7 intermediate points, so ST_Angle returns an array of 7 values.

Without direction (default)

SELECT ST_Angle(ST_MakeTrajectory('LINESTRING(0 0, 0 10, 10 10, 20 10, 30 0, 30 0, 20 10, 0 10, 0 0)'));

        st_angle
-------------------------
 {90,0,45,NaN,NaN,45,90}
(1 row)

With direction

Setting hasdirection to true returns negative values for counterclockwise rotations.

SELECT ST_Angle(ST_MakeTrajectory('LINESTRING(0 0, 0 10, 10 10, 20 10, 30 0, 30 0, 20 10, 0 10, 0 0)'), true);

         st_angle
---------------------------
 {90,0,45,NaN,NaN,-45,-90}
(1 row)