IETF RFC 7035 PDF

This document defines an extension to the Presence Information Data Format Location Object (PIDF-LO) (RFC 4119) for the expression of location information that is defined relative to a reference point. The reference point may be expressed as a geodetic or civic location, and the relative offset may be one of several shapes. An alternative binary representation is described.

Optionally, a reference to a secondary document (such as a map image) can be included, along with the relationship of the map coordinate system to the reference/offset coordinate system, to allow display of the map with the reference point and the relative offset.