The temporal circular buffer type tcbuffer allows to represent the movement of objects together with a circular radius around them. As all temporal types, it comes in three subtypes, namely, instant, sequence, and sequence set. Examples of tcbuffer values in these subtypes are given next.

SELECT tcbuffer 'Cbuffer(Point(1 1), 0.5)@2001-01-01';
SELECT tcbuffer '{Cbuffer(Point(1 1), 0.3)@2001-01-01, Cbuffer(Point(1 1), 0.5)@2001-01-02,
  Cbuffer(Point(1 1), 0.5)@2001-01-03}';
SELECT tcbuffer '[Cbuffer(Point(1 1), 0.2)@2001-01-01, Cbuffer(Point(1 1), 0.4)@2001-01-02,
  Cbuffer(Point(1 1), 0.5)@2001-01-03]';
SELECT tcbuffer '{[Cbuffer(Point(1 1), 1)@2001-01-01, Cbuffer(Point(2 2), 1)@2001-01-02],
  [Cbuffer(Point(2 2), 2)@2001-01-04, Cbuffer(Point(2 2), 3)@2001-01-05]}';

The temporal circular buffer type accepts type modifiers (or typmod in PostgreSQL terminology) to specify the subtype and/or the spatial reference identifier (SRID). The possible values for the subtype are Instant, Sequence, and SequenceSet. The two arguments are optional and if any of them is not specified for a column, values of any subtype and/or SRID are allowed.

SELECT asEWKT(tcbuffer(Sequence,5676) 'SRID=5676;[Cbuffer(Point(1 1), 0.2)@2001-01-01, 
  Cbuffer(Point(1 1), 0.5)@2001-01-03]');
-- SRID=5676;[Cbuffer(POINT(1 1),0.2)@2001-01-01, Cbuffer(POINT(1 1),0.5)@2001-01-03]
SELECT tcbuffer(Sequence) 'Cbuffer(Point(1 1), 0.2)@2001-01-01';
-- ERROR: Temporal type (Instant) does not match column type (Sequence)
SELECT tcbuffer(5676) 'Cbuffer(Point(1 1), 0.2)@2001-01-01';
-- ERROR:  Temporal circular buffer SRID (0) does not match column SRID (5676)

Temporal circular buffer values of sequence or sequence set subtype are converted into a normal form so that equivalent values have identical representations. For this, consecutive instant values are merged when possible. Three consecutive instant values can be merged into two if the linear functions defining the evolution of values are the same. Examples of transformation into a normal form are as follows.

SELECT asText(tcbuffer '[Cbuffer(Point(1 1), 0.2)@2001-01-01,
  Cbuffer(Point(2 2), 0.4)@2001-01-02, Cbuffer(Point(3 3), 0.6)@2001-01-03)');
-- [Cbuffer(Point(1 1),0.2)@2001-01-01, Cbuffer(Point(3 3),0.6)@2001-01-03)
SELECT asText(tcbuffer '{[Cbuffer(Point(1 1), 0.2)@2001-01-01, 
  Cbuffer(Point(2 2), 0.3)@2001-01-02, Cbuffer(Point(2 2), 0.5)@2001-01-03), 
  [Cbuffer(Point(2 2), 0.5)@2001-01-03, Cbuffer(Point(2 2), 0.7)@2001-01-04)}');
/* {[Cbuffer(Point(1 1),0.2)@2001-01-01, Cbuffer(Point(2 2),0.3)@2001-01-02, 
   Cbuffer(Point(2 2),0.7)@2001-01-04)} */