ST_attrDeduplicate

Removes trajectory points with duplicate values in the specified attribute field and returns the deduplicated trajectory object. The first and last trajectory points are always preserved.

Syntax

trajectory ST_attrDeduplicate(trajectory traj, cstring attr_field_name);

Parameters

Parameter	Description
`traj`	The trajectory object.
`attr_field_name`	The name of the attribute field to use for deduplication.

Examples

The following example creates a trajectory with 16 points and deduplicates it by the heading attribute field. Consecutive points with the same heading value are removed, except for the first and last points.

SELECT ST_attrDeduplicate(
  ST_makeTrajectory(
    'STPOINT'::leaftype,
    'LINESTRING(-179.48077 51.72814,-179.46731 51.74634,-179.46502 51.74934,-179.46183 51.75378,-179.45943 51.75736,-179.45560 51.76273,-179.44845 51.77186,-179.43419 51.78977,-179.41259 51.81643,-179.41001 51.81941,-179.40751 51.82223,-179.40497 51.82505,-179.40242 51.82796,-179.39981 51.83095,-179.39734 51.83398,-179.39499 51.83709)'::geometry,
    ARRAY[
      '2017-01-15 09:06:39'::timestamp,
      '2017-01-15 09:13:39',
      '2017-01-15 09:14:48',
      '2017-01-15 09:16:28',
      '2017-01-15 09:17:48',
      '2017-01-15 09:19:48',
      '2017-01-15 09:23:19',
      '2017-01-15 09:30:28',
      '2017-01-15 09:34:40',
      '2017-01-15 09:36:59',
      '2017-01-15 09:38:09',
      '2017-01-15 09:39:18',
      '2017-01-15 09:40:40',
      '2017-01-15 09:47:38',
      '2017-01-15 09:48:49',
      '2017-01-15 21:18:30'
    ],
    '{"leafcount": 16, "attributes": {"heading": {"type": "float", "length": 4, "nullable": false, "value": [23.0,23.0,23.0,23.0,21.0,21.0,72.0,72.0,72.0,72.0,73.0,74.0,73.0,73.0,73.0,73.0]}}}'
  ),
  'heading'
) AS traj;

The output reduces the trajectory from 16 points to 6, keeping only points where the heading value changes and preserving the last point:

{"trajectory":{"version":1,"type":"STPOINT","leafcount":6,"start_time":"2017-01-15 09:17:48","end_time":"2017-01-15 21:18:30","spatial":"LINESTRING(-179.45943 51.75736,-179.44845 51.77186,-179.40751 51.82223,-179.40497 51.82505,-179.39499 51.83709)","timeline":["2017-01-15 09:17:48","2017-01-15 09:23:19","2017-01-15 09:38:09","2017-01-15 09:39:18","2017-01-15 21:18:30"],"attributes":{"leafcount":6,"heading":{"type":"float","length":4,"nullable":false,"value":[23.0,21.0,72.0,73.0,74.0,73.0]}}}}
(1 row)