New IfcPatch recipe to convert units of an IFC file. See #1247.

src/ifcpatch/ifcpatch/recipes/ConvertLengthUnit.py

@@ -0,0 +1,40 @@
+import ifcopenshell
+import ifcopenshell.api
+import ifcopenshell.util.pset
+import ifcopenshell.util.element
+
+
+class Patcher:
+    def __init__(self, src, file, logger, args=None):
+        self.src = src
+        self.file = file
+        self.logger = logger
+        self.args = args
+
+    def patch(self):
+        unit = {"is_metric": "METERS" in self.args[0], "raw": self.args[0]}
+        self.file_patched = ifcopenshell.api.run("project.create_file", version=self.file.schema)
+        project = ifcopenshell.api.run("root.create_entity", self.file_patched, ifc_class="IfcProject")
+        unit_assignment = ifcopenshell.api.run("unit.assign_unit", self.file_patched, **{"length": unit})
+
+        # Is there a better way?
+        for element in self.file.by_type("IfcGeometricRepresentationContext", include_subtypes=False):
+            element.Precision = 1E-8
+
+        # If we don't add openings first, they don't get converted
+        for element in self.file.by_type("IfcOpeningElement"):
+            self.file_patched.add(element)
+
+        for element in self.file:
+            self.file_patched.add(element)
+
+        new_length = [u for u in unit_assignment.Units if u.UnitType == "LENGTHUNIT"][0]
+        old_length = [
+            u for u in self.file_patched.by_type("IfcProject")[1].UnitsInContext.Units if u.UnitType == "LENGTHUNIT"
+        ][0]
+
+        for inverse in self.file_patched.get_inverse(old_length):
+            ifcopenshell.util.element.replace_attribute(inverse, old_length, new_length)
+
+        self.file_patched.remove(old_length)
+        self.file_patched.remove(project)