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Add dimensional-analysis fallback to get_project_unit() for IfcDerivedUnit

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This commit is contained in:
Richard Brice
2026-08-10 14:18:43 -07:00
parent 2b7abcf2e6
commit d11c4411ea
2 changed files with 49 additions and 1 deletions
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src/ifcopenshell-python/ifcopenshell/util/unit.py
+18 -1
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@@ -466,7 +466,16 @@ def cache_units(ifc_file: ifcopenshell.file) -> None:
"""
ifc_file.units = {}
if assignment := get_unit_assignment(ifc_file):
ifc_file.units = {u.UnitType: u for u in assignment.Units if getattr(u, "UnitType", None)}
all_units = assignment.Units or []
units = {u.UnitType: u for u in all_units if getattr(u, "UnitType", None)}
# As in get_project_unit(): a literal match always wins; an IfcDerivedUnit with no
# literal UnitType match is matched dimensionally instead, only to fill a gap.
for unit in all_units:
if unit.is_a("IfcDerivedUnit"):
dimension = identify_unit_dimensions(unit)
if dimension and dimension not in units:
units[dimension] = unit
ifc_file.units = units
def clear_unit_cache(ifc_file: ifcopenshell.file) -> None:
@@ -482,6 +491,10 @@ def get_project_unit(
) -> Union[ifcopenshell.entity_instance, None]:
"""Get the default project unit of a particular unit type
IfcDerivedUnit is matched first by a literal `UnitType` match, then, as a fallback, by
dimensional analysis (:func:`identify_unit_dimensions`), mirroring
:func:`get_candidate_units`.
:param ifc_file: The IFC file.
:param unit_type: The type of unit, taken from the list of IFC unit types,
such as "LENGTHUNIT".
@@ -493,9 +506,13 @@ def get_project_unit(
if units := ifc_file.units:
return units.get(unit_type, None)
if unit_assignment := get_unit_assignment(ifc_file):
dimensional_match = None
for unit in unit_assignment.Units or []:
if getattr(unit, "UnitType", None) == unit_type:
return unit
if dimensional_match is None and unit.is_a("IfcDerivedUnit") and identify_unit_dimensions(unit) == unit_type:
dimensional_match = unit
return dimensional_match
def get_candidate_units(ifc_file: ifcopenshell.file, unit_type: str) -> list[ifcopenshell.entity_instance]: