Empty Geometries

Empty Geometries
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An empty geometry is the empty set of points: it is nowhere. As in PostGIS, an operation gives it the answer the empty set gives, and neither an error nor a notice is raised, except where the geometry must be the position of a value.

-- It meets nothing
SELECT eIntersects(geometry 'Point empty',
  tgeompoint '[Point(1 1)@2001-01-01, Point(2 2)@2001-01-02, Point(1 1)@2001-01-03]');
-- f
SELECT tDisjoint(geometry 'Point empty',
  tgeompoint '[Point(1 1)@2001-01-01, Point(2 2)@2001-01-02, Point(1 1)@2001-01-03]');
-- [t@2001-01-01, t@2001-01-03]
-- Nothing can be measured to it
SELECT geometry 'Point empty' <->
  tgeompoint '[Point(2 2)@2001-01-01, Point(1 1)@2001-01-02, Point(2 2)@2001-01-03]';
-- NULL
-- It removes nothing and keeps nothing
SELECT asText(minusGeometry(tgeompoint '[Point(1 1)@2001-01-01, Point(2 2)@2001-01-02,
  Point(1 1)@2001-01-03]', geometry 'Linestring empty'));
-- [POINT(1 1)@2001-01-01, POINT(2 2)@2001-01-02, POINT(1 1)@2001-01-03]
SELECT asText(atGeometry(tgeompoint '[Point(1 1)@2001-01-01, Point(2 2)@2001-01-02,
  Point(1 1)@2001-01-03]', geometry 'Linestring empty'));
-- NULL
-- It cannot be the position of a value
SELECT tgeompoint(geometry 'Point empty', timestamptz '2001-01-01');
-- ERROR:  Only non-empty geometries accepted

It meets nothing. A relationship asking for a common point, such as intersects, contains, covers, touches, the distance within, and the equality, is false, while disjoint and the inequality are true. A temporal relationship or comparison takes this answer over the whole time of the temporal value, and the ever and always forms answer the same.
Nothing can be measured to it. The distances (|=|, <->, nearestApproachInstant, shortestLine) and bearing are NULL. It has no bounding box, so that stbox, expandSpace, stboxes, splitNStboxes, and splitEachNStboxes are NULL.
It removes nothing and keeps nothing. The restrictions atGeometry and atValue are NULL, since no instant is left, and minusGeometry and minusValue return the temporal value unchanged.
It cannot be the position of a value. Building a temporal value or a set from it, or giving it as the origin of rotate and scale, raises an error.

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