1. C/C++
2. Fundamentals

Getting the Units of the Active Document

by Dale Fugier

This brief guide demonstrates how to determine the unit system of the active document.

Overview

There are two unit systems associated with a document, model and page units. The ON_UnitSystem class makes it easy to work with custom units. The Rhino document class contains two functions:

1. const ON_UnitSystem& ModelUnits() const; and…
2. const ON_UnitSystem& PageUnits() const;

How To

The unit system of the active document is stored on an ON_3dmUnitsAndTolerances class that is located on the CRhinoDoc object.

If you inside of a CRhinoCommand-derived object’s RunCommand() member, you can get the current units system as follows:

const CRhinoDocProperties& doc_props = context.m_doc.Properties();
const ON_3dmUnitsAndTolerances& units = doc_props.ModelUnitsAndTolerances();
ON::unit_system units_system = units.m_unit_system;

As a shortcut, you can do the following:

ON::unit_system units_system = context.m_doc.UnitSystem();

If you outside of a CRhinoCommand-derived object’s RunCommand() member, you can get the current units system as follows:

CRhinoDoc* doc = RhinoApp().ActiveDoc();
if( doc )
{
  ON::unit_system units_system = doc->UnitSystem();
}