OpenSite/Guides/Quantities and profiles
Add quantities written in different units and change their display profile without changing their physical values.
- Stable identifier
opensite.help.quantities-and-profiles
Prerequisites
Embedded OpenSite Python. This lesson does not require a document or a development authorization policy.
Steps
Enter units explicitly
Use parse_quantity or Q rather than assuming that 450 means millimetres. The example combines 3.2 m with 450 mm.
Add compatible quantities
The units engine converts compatible lengths to canonical SI before adding them. Expected total: 3.65 m, or 3650 mm.
Change presentation
Switch to engineering_metric and format the same quantity. Store and compare its SI value before and after. Displaying millimetres must not scale the model.
Handle a rejected unit
Check the unit spelling, physical dimension and quantity kind. Pressure is not a length; absolute temperature differs from a temperature difference.
Expected result
The script prints 3650 mm. Its assertions confirm an SI total of 3.65 m and unchanged SI after selecting the display profile.
Limitations
Profiles affect presentation. They do not choose a national design standard. The script changes the current profile for this session; return to your preferred profile afterwards.
Complete example
import opensite
span = opensite.parse_quantity("3.2 m")
extension = opensite.parse_quantity("450 mm")
total = opensite.add(span, extension)
print(f"Total: {total.value_in('mm'):.0f} mm")
assert abs(total.si_value - 3.65) < 1e-12
before = total.si_value
opensite.execute("units.set_profile", {"profile": "engineering_metric"})
print("Display:", opensite.format_quantity(total, "engineering_metric"))
assert total.si_value == before
