postgis/doc/reference_temporal.xml

<?xml version="1.0" encoding="UTF-8"?>
<sect1 id="Temporal">
	  <title>Temporal Support</title>

		<refentry id="ST_IsValidTrajectory">

		  <refnamediv>
			<refname>ST_IsValidTrajectory</refname>
			<refpurpose>
Returns <varname>true</varname> if the geometry is a valid trajectory.
      </refpurpose>
		  </refnamediv>

		  <refsynopsisdiv>
			<funcsynopsis>
			  <funcprototype>
				<funcdef>boolean <function>ST_IsValidTrajectory</function></funcdef>
				<paramdef><type>geometry </type> <parameter>line</parameter></paramdef>
			  </funcprototype>
			</funcsynopsis>
		  </refsynopsisdiv>

		  <refsection>
			<title>Description</title>

			<para>
Tell if a geometry encodes a valid trajectory.
Valid trajectories are encoded as LINESTRING with M value growing
from each vertex to the next.
			</para>

			<para>
Valid trajectories are expected as input to some spatio-temporal queries
like <xref linkend="ST_ClosestPointOfApproach" />
			</para>
      
			<para>Availability: 2.2.0</para>
			<para>&Z_support;</para>
		  </refsection>


		  <refsection>
			<title>Examples</title>
<programlisting>
-- A valid trajectory
SELECT ST_IsValidTrajectory(ST_MakeLine(
  ST_MakePointM(0,0,1),
  ST_MakePointM(0,1,2))
);
 t

-- An invalid trajectory
SELECT ST_IsValidTrajectory(ST_MakeLine(ST_MakePointM(0,0,1), ST_MakePointM(0,1,0)));
NOTICE:  Measure of vertex 1 (0) not bigger than measure of vertex 0 (1)
 st_isvalidtrajectory
----------------------
 f
</programlisting>
		  </refsection>

		  <!-- Optionally add a "See Also" section -->
		  <refsection>
			<title>See Also</title>
			<para>
<xref linkend="ST_ClosestPointOfApproach" />
			</para>
		  </refsection>
		</refentry>

		<refentry id="ST_ClosestPointOfApproach">

		  <refnamediv>
			<refname>ST_ClosestPointOfApproach</refname>
			<refpurpose>
Returns the measure at which points interpolated along two lines are closest.
      </refpurpose>
		  </refnamediv>

		  <refsynopsisdiv>
			<funcsynopsis>
			  <funcprototype>
				<funcdef>float8 <function>ST_ClosestPointOfApproach</function></funcdef>
				<paramdef><type>geometry </type> <parameter>track1</parameter></paramdef>
				<paramdef><type>geometry </type> <parameter>track2</parameter></paramdef>
			  </funcprototype>
			</funcsynopsis>
		  </refsynopsisdiv>

		  <refsection>
			<title>Description</title>

			<para>
Returns the smallest measure at which point interpolated along the given
lines are at the smallest distance. Inputs must be valid trajectories as
checked by <xref linkend="ST_IsValidTrajectory" />. Null is returned if
the trajectories do not overlap on the M range.
			</para>
      
			<para>
See <xref linkend="ST_LocateAlong" /> for getting the actual points at
the given measure.
			</para>
			
			<para>Availability: 2.2.0</para>
			<para>&Z_support;</para>
		  </refsection>


		  <refsection>
			<title>Examples</title>
<programlisting>
-- Return the time in which two objects moving between 10:00 and 11:00
-- are closest to each other and their distance at that point
WITH inp AS ( SELECT
  ST_AddMeasure('LINESTRING Z (0 0 0, 10 0 5)'::geometry,
    extract(epoch from '2015-05-26 10:00'::timestamptz),
    extract(epoch from '2015-05-26 11:00'::timestamptz)
  ) a,
  ST_AddMeasure('LINESTRING Z (0 2 10, 12 1 2)'::geometry,
    extract(epoch from '2015-05-26 10:00'::timestamptz),
    extract(epoch from '2015-05-26 11:00'::timestamptz)
  ) b
), cpa AS (
  SELECT ST_ClosestPointOfApproach(a,b) m FROM inp
), points AS (
  SELECT ST_Force3DZ(ST_GeometryN(ST_LocateAlong(a,m),1)) pa,
         ST_Force3DZ(ST_GeometryN(ST_LocateAlong(b,m),1)) pb
  FROM inp, cpa
)
SELECT to_timestamp(m) t,
       ST_Distance(pa,pb) distance
FROM points, cpa;

               t               |     distance
-------------------------------+------------------
 2015-05-26 10:45:31.034483+02 | 1.96036833151395
</programlisting>
		  </refsection>

		  <!-- Optionally add a "See Also" section -->
		  <refsection>
			<title>See Also</title>
			<para>
<xref linkend="ST_IsValidTrajectory" />,
<xref linkend="ST_DistanceCPA" />,
<xref linkend="ST_LocateAlong" />,
<xref linkend="ST_AddMeasure" />
			</para>
		  </refsection>
		</refentry>

		<refentry id="ST_DistanceCPA">

		  <refnamediv>
			<refname>ST_DistanceCPA</refname>
			<refpurpose>
Returns the distance between closest points of approach in two trajectories.
      </refpurpose>
		  </refnamediv>

		  <refsynopsisdiv>
			<funcsynopsis>
			  <funcprototype>
				<funcdef>float8 <function>ST_DistanceCPA</function></funcdef>
				<paramdef><type>geometry </type> <parameter>track1</parameter></paramdef>
				<paramdef><type>geometry </type> <parameter>track2</parameter></paramdef>
			  </funcprototype>
			</funcsynopsis>
		  </refsynopsisdiv>

		  <refsection>
			<title>Description</title>

			<para>
Returns the minimum distance two moving objects have ever been each-other.
Inputs must be valid trajectories as checked by
<xref linkend="ST_IsValidTrajectory" />.
Null is returned if the trajectories do not overlap on the M range.
			</para>
      
			<para>Availability: 2.2.0</para>
			<para>&Z_support;</para>
		  </refsection>


		  <refsection>
			<title>Examples</title>
<programlisting>
-- Return the minimum distance of two objects moving between 10:00 and 11:00
WITH inp AS ( SELECT
  ST_AddMeasure('LINESTRING Z (0 0 0, 10 0 5)'::geometry,
    extract(epoch from '2015-05-26 10:00'::timestamptz),
    extract(epoch from '2015-05-26 11:00'::timestamptz)
  ) a,
  ST_AddMeasure('LINESTRING Z (0 2 10, 12 1 2)'::geometry,
    extract(epoch from '2015-05-26 10:00'::timestamptz),
    extract(epoch from '2015-05-26 11:00'::timestamptz)
  ) b
)
SELECT ST_DistanceCPA(a,b) distance FROM inp;

     distance
------------------
 1.96036833151395
</programlisting>
		  </refsection>

		  <!-- Optionally add a "See Also" section -->
		  <refsection>
			<title>See Also</title>
			<para>
<xref linkend="ST_IsValidTrajectory" />,
<xref linkend="ST_ClosestPointOfApproach" />,
<xref linkend="ST_AddMeasure" />,
<xref linkend="geometry_distance_cpa" />
			</para>
		  </refsection>
		</refentry>

		<refentry id="ST_CPAWithin">

		  <refnamediv>
			<refname>ST_CPAWithin</refname>
			<refpurpose>
Returns true if the trajectories' closest points of approach
are within the specified distance.
      </refpurpose>
		  </refnamediv>

		  <refsynopsisdiv>
			<funcsynopsis>
			  <funcprototype>
				<funcdef>float8 <function>ST_CPAWithin</function></funcdef>
				<paramdef><type>geometry </type> <parameter>track1</parameter></paramdef>
				<paramdef><type>geometry </type> <parameter>track2</parameter></paramdef>
				<paramdef><type>float8 </type> <parameter>maxdist</parameter></paramdef>
			  </funcprototype>
			</funcsynopsis>
		  </refsynopsisdiv>

		  <refsection>
			<title>Description</title>

			<para>
Checks whether two moving objects have ever been within the
specified max distance.
      </para>
			<para>
Inputs must be valid trajectories as checked by
<xref linkend="ST_IsValidTrajectory" />.
False is returned if the trajectories do not overlap on the M range.
			</para>
      
			<para>Availability: 2.2.0</para>
			<para>&Z_support;</para>
		  </refsection>


		  <refsection>
			<title>Examples</title>
<programlisting>
WITH inp AS ( SELECT
  ST_AddMeasure('LINESTRING Z (0 0 0, 10 0 5)'::geometry,
    extract(epoch from '2015-05-26 10:00'::timestamptz),
    extract(epoch from '2015-05-26 11:00'::timestamptz)
  ) a,
  ST_AddMeasure('LINESTRING Z (0 2 10, 12 1 2)'::geometry,
    extract(epoch from '2015-05-26 10:00'::timestamptz),
    extract(epoch from '2015-05-26 11:00'::timestamptz)
  ) b
)
SELECT ST_CPAWithin(a,b,2), ST_DistanceCPA(a,b) distance FROM inp;

 st_cpawithin |     distance
--------------+------------------
 t            | 1.96521473776207
</programlisting>
		  </refsection>

		  <!-- Optionally add a "See Also" section -->
		  <refsection>
			<title>See Also</title>
			<para>
<xref linkend="ST_IsValidTrajectory" />,
<xref linkend="ST_ClosestPointOfApproach" />,
<xref linkend="ST_DistanceCPA" />,
<xref linkend="geometry_distance_cpa" />
			</para>
		  </refsection>
		</refentry>

  </sect1>