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For all geometries (Surface, ElevatedPoint, etc.) a CRS shall be specified. The CRS is either defined directly on the geometry element using the srsName attribute or is derived from the larger context the geometry is part of.
In the latter case, the CRS defined applies to all geometrical elements in the AIXM file, except for those AIXM geometrical elements that have their own srsName defined.
Unless overruled by the presence of a local srsName for convenience in constructing feature and feature collection instances, the value of the srsName attribute on the gml:Envelope shall be inherited by all directly expressed geometries in all properties of the feature or members of the collection. As indicated in the Figure below, the gml:Envelope is a child element of the gml:boundedBy property of the feature. If a geometry uses the same coordinate reference system as given on the gml:boundedBy property of its parent feature that geometry does not require a srsName attribute,
Inheritance of the coordinate reference system continues to any depth of nesting. However, if overruled by a local srsName declaration, then the new coordinate reference system is inheritedby inherited by all its children in turn.
Notwithstanding this rule, all the geometries used in a feature or feature collection may carry srsName attributes. This is in order to indicate a local reference system, even if they are the same as the parent. A geometry without a srsName derives its CRS from its closest ancestor that has a srsName. Due to the way that AIXM is modelled, this can only be one of the following:
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