The temporal circular buffer type tcbuffer allows to represent the movement of objects together with a circular radius around them. It corresponds to the temporal point type tgeompoint restricted to two-dimensional coordinates. As all the other temporal types it comes in trhee 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). The possible values for the type modifier are Instant, Sequence, and SequenceSet. If no type modifier is specified for a column, values of any subtype are allowed.

SELECT tcbuffer(Sequence) '[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(Sequence) 'Cbuffer(Point(1 1), 0.2)@2001-01-01';
-- ERROR: Temporal type (Instant) does not match column type (Sequence)

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)} */