Change the unit of the IFC file from mm to cm

[u0416033]

I have a IFC file with unit mm and I have to load it on the website with three.js . The IFC is too big so that out of the memory .I try to change the unit of the file and it is the code I try to use . Console outputs all of the attributes that unit will be affect by unit but the IFC file do not change with the code . How can I fix it?

//-------------------------------code [----------------------------------------]from(#1247)

ifc_file  = ifcopenshell.open('專案座標_東10000北5.ifc')


def calculate_unit_scale(file):
    units = file.by_type("IfcUnitAssignment")[0]
    unit_scale = 1
    for unit in units.Units:
        if not hasattr(unit, "UnitType") or unit.UnitType != "LENGTHUNIT":
            continue
        while unit.is_a("IfcConversionBasedUnit"):
            unit_scale *= unit.ConversionFactor.ValueComponent.wrappedValue
            unit = unit.ConversionFactor.UnitComponent
        if unit.is_a("IfcSIUnit"):
            unit_scale *= get_prefix_multiplier(unit.Prefix)
    return unit_scale


s = ifcopenshell.ifcopenshell_wrapper.schema_by_name("IFC4")
classes_to_modify = {}
for d in s.declarations():
    if not hasattr(d, "all_attributes") or "IfcLength" not in str(d.all_attributes()):
        continue
    attributes_to_modify = []
    for attribute in d.all_attributes():
        if "IfcLength" in str(attribute):
            attributes_to_modify.append(attribute.name())
    classes_to_modify[d.name()] = attributes_to_modify

print(classes_to_modify)



def scale_all(obj, sf):
    def serialize(obj):
        """Recursively walk object's hierarchy."""
        if isinstance(obj, (int, float)):
            return obj * sf
        elif isinstance(obj, list):
            return [serialize(item) for item in obj]
        elif isinstance(obj, tuple):
            return tuple(serialize([item for item in obj]))
        else:
            try:
                if obj.is_a('IfcLengthMeasure') is True:
                    obj.wrappedValue = obj.wrappedValue * sf
                    return obj
                elif obj.is_a('IfcReal') is True:
                    obj.wrappedValue = obj.wrappedValue * sf
                    return obj
                elif obj.is_a('IfcInteger') is True:
                    obj.wrappedValue = int(obj.wrappedValue * sf)
                    return obj
                elif obj.is_a('IfcPlaneAngleMeasure') is True:
                    obj.wrappedValue = obj.wrappedValue * sf
                    return obj
                elif obj.is_a('IfcText') is True:
                    return obj
                elif obj.is_a('IfcLogical') is True:
                    return obj
            except:
                pass

            raise ValueError(f'Unknown entity "{type(obj)}", "{obj}"')

    return serialize(obj)


for ifc_class, attributes in classes_to_modify.items():
    for element in ifc_file.by_type(ifc_class):
        for attribute in attributes:

            old_val = getattr(element, attribute)
            if old_val is None:
                continue
            setattr(element, attribute, scale_all(old_val, 10))
            new_val = getattr(element, attribute)

[Moult]

You can use IfcPatch for this: https://blenderbim.org/docs-python/ifcpatch.html

One of the recipes converts length units: https://blenderbim.org/docs-python/autoapi/ifcpatch/recipes/ConvertLengthUnit/index.html

The underlying code is here: https://github.com/IfcOpenShell/IfcOpenShell/blob/v0.7.0/src/ifcpatch/ifcpatch/recipes/ConvertLengthUnit.py

[Moult]

Thanks for persisting and helping find bugs!

[u0416033]

@Moult Hi ,sorry .I still have some problem for the ifcpatch. I find that after I use the recipe of ConvertLengthUnit , the model does not modify correctly. Like the screenshot below.

but it look like this originally

Can this problem be fixed?
my code :
`
ifc_file = ifcopenshell.open('南屯區永富段95、96地號測試檔(coRFR)-0731-mm.ifc')

output = ifcpatch.execute({
"input": ifc_file,
"file": ifc_file,
"recipe": "ConvertLengthUnit",
"arguments": ["CENTIMETERS"]
})
ifcpatch.write(output, "南屯區永富段95、96地號測試檔(coRFR)-0731-mm-modify.ifc")
`

[Moult]

Can you share your model? Send to dion@thinkmoult.com if private.

[u0416033]

@Moult Hi ! Sorry for late reply,I have send the ifc file with email.

[u0416033]

@Moult
Hello Moult. I am wondering if you have received the model file that I sent you. If so, were you able to run the function that corrects the model units? Thank you very much!