List of documented conversion based units misses plane angle units.

[TLiebich]

the following list describes conversion based units defined within IFC.
see latest definition at IfcConversionBasedUnit.

it defined degree [0..360] as a unit
in surveying (and infrastructure) gradian (or gon) is used [0..400]

it should be added.

for both, full double precision should be used:

• 0.017453292519943295 for degrees
• 0.015707963267948967 for gradian.