The simple type gml:TimePositionUnion is a union of XML Schema simple types which instantiate the subtypes for temporal position described in ISO 19108.<br/> An ordinal era may be referenced via URI.  A decimal value may be used to indicate the distance from the scale origin .  time is used for a position that recurs daily (see ISO 19108:2002 5.4.4.2).<br/> Finally, calendar and clock forms that support the representation of time in systems based on years, months, days, hours, minutes and seconds, in a notation following ISO 8601, are assembled by gml:CalDate<br/>