Fix #1795. New support for conversion based units with offsets, like fahrenheit.

src/ifcopenshell-python/ifcopenshell/api/unit/add_conversion_based_unit.py

@@ -5,33 +5,29 @@ import ifcopenshell.util.unit
 class Usecase:
     def __init__(self, file, **settings):
         self.file = file
-        self.settings = {"unit_type": "LENGTHUNIT", "name": "METRE", "prefix": None, "conversion_offset": None}
+        self.settings = {"name": "foot", "conversion_offset": None}
         for key, value in settings.items():
             self.settings[key] = value
 
     def execute(self):
-        if self.settings["unit_type"] == "LENGTHUNIT":
-            dimensional_exponents = self.file.createIfcDimensionalExponents(1, 0, 0, 0, 0, 0, 0)
-            si_unit = self.file.createIfcSIUnit(UnitType=self.settings["unit_type"], Name="METRE")
-        elif self.settings["unit_type"] == "AREAUNIT":
-            dimensional_exponents = self.file.createIfcDimensionalExponents(2, 0, 0, 0, 0, 0, 0)
-            si_unit = self.file.createIfcSIUnit(UnitType=self.settings["unit_type"], Name="SQUARE_METRE")
-        elif self.settings["unit_type"] == "VOLUMEUNIT":
-            dimensional_exponents = self.file.createIfcDimensionalExponents(3, 0, 0, 0, 0, 0, 0)
-            si_unit = self.file.createIfcSIUnit(UnitType=self.settings["unit_type"], Name="CUBIC_METRE")
+        unit_type = ifcopenshell.util.unit.imperial_types.get(self.settings["name"], "USERDEFINED")
+        dimensions = ifcopenshell.util.unit.named_dimensions[unit_type]
+        exponents = self.file.createIfcDimensionalExponents(*dimensions)
+        si_name = ifcopenshell.util.unit.si_type_names[unit_type]
+        si_unit = self.file.createIfcSIUnit(UnitType=unit_type, Name=si_name)
 
         conversion_real = ifcopenshell.util.unit.si_conversions.get(self.settings["name"], 1)
         value_component = self.file.create_entity("IfcReal", **{"wrappedValue": conversion_real})
         conversion_factor = self.file.createIfcMeasureWithUnit(value_component, si_unit)
 
-        if self.settings["conversion_offset"]:
-            return self.file.createIfcConversionBasedUnit(
-                dimensional_exponents,
-                self.settings["unit_type"],
-                self.settings["name"],
-                conversion_factor,
-                self.settings["conversion_offset"],
+        conversion_offset = self.settings["conversion_offset"]
+        if not conversion_offset:
+            conversion_offset = ifcopenshell.util.unit.si_offsets.get(self.settings["name"], 0)
+
+        if conversion_offset:
+            return self.file.createIfcConversionBasedUnitWithOffset(
+                exponents, unit_type, self.settings["name"], conversion_factor, conversion_offset,
             )
         return self.file.createIfcConversionBasedUnit(
-            dimensional_exponents, self.settings["unit_type"], self.settings["name"], conversion_factor
+            exponents, unit_type, self.settings["name"], conversion_factor
         )

src/ifcopenshell-python/ifcopenshell/util/unit.py

@@ -192,9 +192,14 @@ si_conversions = {
     "hour": 3600,
     "day": 86400,
     "btu": 1055.056,
+    "fahrenheit": 1.8,
 }
 
 
+si_offsets = {
+    "fahrenheit": -459.67,
+}
+
 
 imperial_types = {
     "thou": "LENGTHUNIT",
@@ -233,6 +238,7 @@ imperial_types = {
     "hour": "TIMEUNIT",
     "day": "TIMEUNIT",
     "btu": "ENERGYUNIT",
+    "fahrenheit": "THERMODYNAMICTEMPERATUREUNIT",
 }
 
 

src/ifcopenshell-python/test/api/unit/test_add_conversion_based_unit.py

@@ -0,0 +1,43 @@
+import test.bootstrap
+import ifcopenshell.api
+
+
+class TestAddConversionBasedUnit(test.bootstrap.IFC4):
+    def test_run(self):
+        unit = ifcopenshell.api.run("unit.add_conversion_based_unit", self.file, name="foot")
+        assert unit.is_a("IfcConversionBasedUnit")
+        assert unit.Dimensions.LengthExponent == 1
+        assert unit.Dimensions.MassExponent == 0
+        assert unit.Dimensions.TimeExponent == 0
+        assert unit.Dimensions.ElectricCurrentExponent == 0
+        assert unit.Dimensions.ThermodynamicTemperatureExponent == 0
+        assert unit.Dimensions.AmountOfSubstanceExponent == 0
+        assert unit.Dimensions.LuminousIntensityExponent == 0
+        assert unit.UnitType == "LENGTHUNIT"
+        assert unit.Name == "foot"
+        assert unit.ConversionFactor.ValueComponent.wrappedValue == 0.3048
+        si_unit = unit.ConversionFactor.UnitComponent
+        assert si_unit.is_a("IfcSIUnit")
+        assert si_unit.UnitType == "LENGTHUNIT"
+        assert si_unit.Prefix is None
+        assert si_unit.Name == "METRE"
+
+    def test_adding_a_unit_with_offset(self):
+        unit = ifcopenshell.api.run("unit.add_conversion_based_unit", self.file, name="fahrenheit")
+        assert unit.is_a("IfcConversionBasedUnitWithOffset")
+        assert unit.Dimensions.LengthExponent == 0
+        assert unit.Dimensions.MassExponent == 0
+        assert unit.Dimensions.TimeExponent == 0
+        assert unit.Dimensions.ElectricCurrentExponent == 0
+        assert unit.Dimensions.ThermodynamicTemperatureExponent == 1
+        assert unit.Dimensions.AmountOfSubstanceExponent == 0
+        assert unit.Dimensions.LuminousIntensityExponent == 0
+        assert unit.UnitType == "THERMODYNAMICTEMPERATUREUNIT"
+        assert unit.Name == "fahrenheit"
+        assert unit.ConversionFactor.ValueComponent.wrappedValue == 1.8
+        si_unit = unit.ConversionFactor.UnitComponent
+        assert si_unit.is_a("IfcSIUnit")
+        assert si_unit.UnitType == "THERMODYNAMICTEMPERATUREUNIT"
+        assert si_unit.Prefix is None
+        assert si_unit.Name == "KELVIN"
+        assert unit.ConversionOffset == -459.67