API reference / @zaes/tactical-graphics / AltitudeDatum

Enumeration: AltitudeDatum

Defined in: tacticalgraphics/core/type.ts:1549

What an altitude is measured from.

FM 1-02.2's field X carries a number plus the thing it is relative to — the plates print 1500FT AGL and 20000FT AGL, and the field description's own examples are 1500MSL and FL150. The datum belongs to the value, not to the host: two zones on one map can honestly be one AGL and one MSL, so a global setting could never say so. That is why this is a graphic property while AltitudeUnit is configuration.

• MSL — above mean sea level. A true height from a real datum.
• AGL — above ground level. Also a true height, and a different one: 1500 AGL over a 3000 ft ridge is 4500 MSL, which is why the two cannot be folded together.
• FL — a flight level: hundreds of feet of pressure altitude against the standard 1013.25 hPa setting. Deliberately not a height above anything — above the transition altitude every aircraft uses the same reference, so flight levels separate aircraft from each other rather than placing them. It renders as FL150, with no unit and the number meaning 15,000 ft, which is why it takes its own branch in formatAltitude rather than a suffix.

Enumeration Members

Enumeration Member	Value	Defined in
aboveGroundLevel	"AGL"	tacticalgraphics/core/type.ts:1551
flightLevel	"FL"	tacticalgraphics/core/type.ts:1552
meanSeaLevel	"MSL"	tacticalgraphics/core/type.ts:1550