IfcSIUnit.Dimensions is a schema-derived attribute that isn't computed for
Bonsai's SQLite-linked "large model" file representation, returning None
there instead of an IfcDimensionalExponents entity. #9278 added an
unconditional unit.Dimensions.LengthExponent access to every IfcSIUnit
processed by calculate_unit_scale(), so it crashed project loading for
any linked file, even ones with no unit prefixes at all -- not just the
prefixed-area/volume case the fix targeted.
Fixed by reading dimensions from the existing si_dimensions table (keyed
by the unit's stored Name, not the unresolvable derived attribute) instead
of unit.Dimensions.
See the PR discussion for a standalone reproduction script.
An SI prefix attaches to the base unit symbol and the prefixed symbol is
raised to the power as a whole: DECI CUBIC_METRE is dm3 = a litre = 1e-3 m3,
not 0.1 m3. The scale factor previously applied the prefix multiplier
linearly for all IfcSIUnits, inflating volumes x100 and areas x10 for such
declarations (produced e.g. by MagiCAD for Revit MEP exports).
Following the reviewer note in #9278, the exponent is taken from the
derived attribute IfcSIUnit.Dimensions rather than from substring matching
on the unit name: the multiplier is raised to LengthExponent only when the
unit's dimensions are a pure power of length, so prefixed derived units
(KILO PASCAL, MEGA NEWTON) and non-length units (KILO GRAM) correctly keep
the linear multiplier. This matches the exponent handling already present
in convert() and named_dimensions in the same module.
Adds regression tests for prefixed AREAUNIT/VOLUMEUNIT and for the
linear-prefix behaviour of PRESSUREUNIT/MASSUNIT.
IfcGeometricRepresentationContext.Precision is typed as a plain IfcReal
but is interpreted in the project length unit, so the IfcLengthMeasure
traversal in convert_file_length_units never touched it. A model
converted from mm to m kept a Precision of e.g. 0.01 (fine in mm, huge
in m), which breaks downstream geometry interpretation such as
IfcConvert boolean cleanup.
Subcontexts derive Precision from their parent, so only root contexts
are scaled.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Centralises the millimetre-to-metre conversion shortcut that
add_door_representation and add_window_representation each defined
locally. Subsequent commits in this PR switch both call sites to
import this from util.unit, removing the duplicate definitions.
Generated with the assistance of an AI coding tool.
Richard Brice