The obstacle geometry and location properties as listed in PANS-AIM Appendix 6 map to AIXM 5.1(.1) elements that appear in the following diagram.

The following table provides more information on the geometry and location properties, including the corresponding names in Table A6-2 and the Data Catalogue. This is important as the two sources used to define the basic properties are not always consistent.

geometry and location property	PANS-AIM Table A6-2 Obstacle attribute	PANS AIM Data Catalogue A1-6 Obstacle data	Description (PANS-AIM Data catalogue)	Corresponding AIXM 5.1 element	Remarks
Geometry type	Geometry type	Geometry type	An indication whether the obstacle is a point, line or polygon	VerticalStructurePartGeometry.surfaceExtent VerticalStructurePartGeometry.linearExtent VerticalStructurePartGeometry.location	According to PANS-AIM, 5.3.3.2.2.1 - "Obstacle data elements are features that shall be represented in the data sets by points, lines or polygons." Description from the EUROCONTROL TOD Manual : "An indication of how the obstacle is described, in respect of whether it is a point, line or polygon (data level)." The RTCA DO-276 /ED-98 "User Requirements for Terrain and Obstacle data" indicates that: "A point is the smallest unit of geometry and has no spatial extent. Points are described by two-dimensional (2D) or three-dimensional (3D) coordinates." "A line consists of a connected sequence of points: a startpoint, an endpoint, and any number of vertices. A vertex is a connecting point in between the startpoint and endpoint. A connection between vertices, or between a vertex and a startpoint or endpoint, is a straight line." "A polygon is a surface described by a closed line (i.e., a line whose startpoint and endpoint are coincident). The closed line forms the outer edge of the surface. The inside of the polygon is defined by the left side in the order of vertices." Because the geometry can be coded separately for each VerticalStructurePart, the AIXM model also allows the coding of obstacles with mixed geometry. For example, a power line can be coded as a single VerticalStructure with multiple parts, each having a line geometry (for the cable) or a point geometry (for the supports of the cable).
Horizontal extent	Horizontal extent	Horizontal extent	Horizontal extent of the obstacle	VerticalStructure.radius	RTCA DO-276 /ED-98 defines horizontal extent as "the footprint of or the area subtended by the obstacle, e.g., area covered by mast guy wires, or weather balloon." Data capture rules explain that "a point obstacle shall have a horizontal extent using the radius attribute, when its footprint above the collection surface is significant and has a potential impact on safety (e.g. radius > ½ required horizontal accuracy)". The TOD Manual indicates that "the horizontal extent could be used to indicate the horizontal footprint of an obstacle (data level). Given that the geometry type already describes the profile of an obstacle, it is recommended that this attribute is only used for point or line obstacles, to indicate the level of geometric simplification". Note that AIXM also provides attributes for coding the overall length (VerticalStructure.length) and width (VerticalStructure.width) of the obstacle, when relevant.
Horizontal position	Horizontal position	Horizontal position	Horizontal position of obstacle	VerticalStrucurePart.location.ElevatedPoint VerticalStrucurePart.linearExtent.ElevatedCurve VerticalStrucurePart.surfaceExtent.ElevatedSurface	For line or polygon obstacles, the position is provided for each vertex that composes the curve or surface, as applicable.
Horizontal reference system	Horizontal reference system	-	[...] the mathematical reference ellipsoid which define the position of a point on the surface of the Earth	ElevatedPoint.gmlPos@srsName ElevatedCurve.gml:posList@srsname ElevatedSurface.gml:posList@srsName	The horizontal reference system is provided in the form of an srsName, which uniquely identifies a Geodetic Coordinate Reference System (CRS).
Horizontal accuracy	Horizontal accuracy	-	A degree of conformance between the estimated or measured value and the true value.	ElevatedPoint.horizontalAccuracy ElevatedCurve.horizontalAccuracy ElevatedSurface.horizontalAccuracy	For line or polygon obstacles, it is also possible to provide the horizontal accuracy of each vertex that composes the curve or surface, using a gml:pointProperty element. AIXM 5.1.1 issue The current definition of the horizontalAccuracy attribute says that it is "... expressed as a circular error at 95 percent probability". This is incorrect for obstacle data because the ICAO requirements indicate only 90 percent probability. An issue has been raised in the AIXM Change Control Board and it is expected that the definition will be corrected in the next AIXM version (5.2).
Horizontal resolution	Horizontal resolution	-	A number of units or digits to which a measured or calculated value is expressed and used.	ElevatedPoint.annotation ElevatedCurve.annotation ElevatedSurface.annotation	In AIXM 5.1, the resolution is implicit, by the number of significant digits. AIXM 5.1.1 issue There is no dedicated attribute in AIXM 5.1.1. A Note may be used to encoding an explicit resolution value, if different from the number of digits actually used. An issue has been raised in the AIXM Change Control Board and it is possible that explicit "numerical resolution" properties are added in the next AIXM version (5.2).
Horizontal confidence level	Horizontal confidence level	-	The probability that the true value of a parameter is within a certain interval around the estimate of its value.	MD_Metadata Note: This is defined for the data set	According to the latest TOD Manual, the horizontal confidence level is considered metadata at the level of the data set.
Elevation	Elevation	Elevation	Elevation of the highest point of the obstacle.	VerticalStrucurePart.location.ElevatedPoint.elevation VerticalStrucurePart.linearExtent.ElevatedCurve.elevation VerticalStrucurePart.surfaceExtent.ElevatedSurface.elevation	The elevation is considered at the top of the obstacle.
Height	Height	Height	Height of the obstacle above ground	VerticalStrucurePart.verticalExtent	In AIXM, for obstacle parts that sit on the ground, the vertical extent is equal to the height above ground. For obstacle parts that are not physically seated on the ground (such as a bridge or cable), the meaning of and the requirements for "height" will be further discussed in the coding guidelines. RTCA DO-276 /ED-98 defines height as "the maximum vertical distance of an obstacle, measured from its base (ground level) to the top." The TOD Manual explains that "whilst the elevation of an obstacle typically comprises its height above MSL, its height above ground level should also be measured (data level). It should, however, be noted that the key information is the elevation of the obstacle and that the height above ground for an obstacle may vary depending on the position at which it is measured and an uneven ground profile." AIXM 5.1.1 issue An issue has been raised in the AIXM Change Control Board and it is possible that a "height" property for VerticalStructurePart is added in the next AIXM version (5.2).
Vertical reference system	Vertical reference system	-	A specific datum from which the vertical distance of a level, point or an object considered as a point is measured.	ElevatedPoint.verticalDatum ElevatedCurve.verticalDatum ElevatedSurface.verticalDatum
Vertical accuracy	Vertical accuracy	-	A degree of conformance between the estimated or measured value and the true value.	ElevatedPoint.verticalAccuracy ElevatedCurve.verticalAccuracy ElevatedSurface.verticalAccuracy
Vertical resolution	Vertical resolution	-	A number of units or digits to which a measured or calculated value is expressed and used.	ElevatedPoint.annotation ElevatedCurve.annotation ElevatedSurface.annotation	In AIXM 5.1, the resolution is implicit, by the number of significant digits. AIXM 5.1.1 issue There is no dedicated attribute in AIXM 5.1.1. A Note may be used to encoding an explicit resolution value, if different from the number of digits actually used. An issue has been raised in the AIXM Change Control Board and it is possible that explicit "numerical resolution" properties are added in the next AIXM version (5.2).
Vertical confidence level	Vertical confidence level	-	The probability that the true value of a parameter is within a certain interval around the estimate of its value.	MD_Metadata Note: This is defined for the data set	According to the latest TOD Manual, the vertical confidence level is considered metadata at the level of the data set.
Unit of measurement used	Unit of measurement used	-	none	VerticalStructure.radius.@uom VerticalStructure.length.@uom VerticalStructure.width.@uom ElevatedPoint.horizontalAccuracy.@uom ElevatedCurve.horizontalAccuracy.@uom ElevatedSurface.horizontalAccuracy.@uom ElevatedPoint.elevation.@uom ElevatedCurve.elevation.@uom ElevatedSurface.elevation.@uom VerticalStrucurePart.verticalExtent.@uom	In AIXM, each dimension value has its own unit of measurement (defined as part of the corresponding data type).
Operations	Operations	Operations	Feature operations of mobile obstacles	VerticalStructurePart.mobile	According to PANS-AIM 5.3.3.2.2.2 Note. - "By definition, obstacles can be fixed (permanent or temporary) or mobile. Specific attributes associated with mobile (feature operations) and temporary types of obstacles are annotated in Appendix 6, Table A6-2, as optional attributes. If these types of obstacles are to be provided in the data set, appropriate attributes describing such obstacles are also required." AIXM also provides the possibility to provide a schedule for each VerticalStructurePart. For a mobile obstacle or an obstacle with moving parts, this allows to code the times at which that part effectively exists at the location and with the associated properties (such as horizontal and vertical extent, etc.)

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