ApsaraDB RDS:ST_Angle

Syntax

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

Parameters

Description

For a trajectory with n points, ST_Angle computes the rotation angle at each of the n - 2 intermediate points (excluding the first and last points).

The return value at each intermediate point follows these rules:

• 0 — the trajectory moves in a straight line at that point.

• NaN — the trajectory stays at the same position at that point (zero displacement).

When hasdirection is false (the default), all angles are returned as positive values regardless of rotation direction. When hasdirection is true, counterclockwise rotation returns a negative angle.

Examples

The following examples use the same nine-point trajectory. The trajectory has 7 intermediate points, so both queries return an array of 7 values.

Example 1: Without direction (default)

SELECT ST_Angle(
  ST_MakeTrajectory(
    'STPOINT'::leaftype,
    'LINESTRING(0 0, 0 10, 10 10, 20 10, 30 0, 30 0, 20 10, 0 10, 0 0)',
    '2000-01-01',
    '2000-01-01'::timestamp + '1 day'::interval
      * (ST_NPoints('LINESTRING(0 0, 0 10, 10 10, 20 10, 30 0, 30 0, 20 10, 0 10, 0 0)') - 1),
    '{}'
  )
);

Result:

      st_angle
-------------------------
 {90,0,45,NaN,NaN,45,90}

Example 2: With direction

SELECT ST_Angle(
  ST_MakeTrajectory(
    'STPOINT'::leaftype,
    'LINESTRING(0 0, 0 10, 10 10, 20 10, 30 0, 30 0, 20 10, 0 10, 0 0)',
    '2000-01-01',
    '2000-01-01'::timestamp + '1 day'::interval
      * (ST_NPoints('LINESTRING(0 0, 0 10, 10 10, 20 10, 30 0, 30 0, 20 10, 0 10, 0 0)') - 1),
    '{}'
  ),
  true
);

Result:

       st_angle
---------------------------
 {90,0,45,NaN,NaN,-45,-90}

The last two values change from 45, 90 to -45, -90 because the trajectory turns counterclockwise at those points.