add conversion based unit symbols

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

@@ -296,6 +296,44 @@ unit_symbols = {
     "square foot": "ft2",
     "square yard": "yd2",
     "square mile": "mi2",
+    # conversion based units
+    "thou": "th",
+    "inch": "in",
+    "foot": "ft",
+    "yard": "yd",
+    "mile": "mi",
+    "square thou": "th2",
+    "square inch": "in2",
+    "square foot": "ft2",
+    "square yard": "yd2",
+    "acre": "ac",
+    "square mile": "mi2",
+    "cubic thou": "th3",
+    "cubic inch": "in3",
+    "cubic foot": "ft3",
+    "cubic yard": "yd3",
+    "cubic mile": "mi3",
+    "litre": "L",
+    "fluid ounce UK": "fl oz",
+    "fluid ounce US": "fl oz",
+    "pint UK": "pt",
+    "pint US": "pt",
+    "gallon UK": "gal",
+    "gallon US": "gal",
+    "degree": "°",
+    "ounce": "oz",
+    "pound": "lb",
+    "ton UK": "ton",
+    "ton US": "ton",
+    "lbf": "lbf",
+    "kip": "kip",
+    "psi": "psi",
+    "ksi": "ksi",
+    "minute": "min",
+    "hour": "hr",
+    "day": "day",
+    "btu": "btu",
+    "fahrenheit": "°F",
 }