Numerical values
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Vertical limits are typically encoded in AIXM as a pair of two attributes:
- a "...Limit" attribute, which includes the value and its unit of measurement (as an "uom" attribute) with the list of values: UomDistanceVerticalType;
- a "...LimitReference" attribute, which indicates what reference system is used for the vertical limit value. It uses the following list of values: CodeVerticalReferenceType;
The following consistency rules between the uom value and the reference value shall be observed when encoding the data:
| Reference | Reference Meaning | Possible uom values |
|---|---|---|
| SFC | Height (above surface) | FT, M |
| MSL | Elevation (above mean sea level) | FT, M |
| W84 | Ellipsoidal height (above the WGS 84 Ellipsoid) - currently not used for aeronautical operations | FT, M |
| STD | Pressure difference expressed as an equivalent vertical distance | FT, SM |
| OTHER: MY_VALUE | Exact meaning depends on what "MY_VALUE" says | FT, M |
Coded values (GND, UNL, etc.)
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As the unit of measurement attribute is mandatory in AIXM for all “...Limit” attributes, the following values are recommended when encoding the data:
| Coded Value | uom (mandatory) |
|---|---|
| GND | FT |
| UNL | FT |
| FLOOR | OTHER |
| CEILING | OTHER |
The "...Reference" attribute shall be left empty in this situation. However, even if another uom is used or even if the "...Reference" attribute gets a value, they should be ignored by a recipient application because they do not have any meaning in combination with these coded values.
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