Changing Display Precision

This brief guide demonstrates how to change the unit's display precision of the current document using C/C++.


Rhino has a document display precision - the “display precision” option found in the Units page in the Options dialog. Imagine you want to modify this using C/C++ from your plugin.


A document’s display precision, the number of decimal places used for the distance display, is maintained on an ON_3dmUnitsAndTolerances object, which in turn is stored on a CRhinoDocProperties object which is a member of the current CRhinoDoc object. To modify this variable, you will need to:

  1. Make a copy of the document’s ON_3dmUnitsAndTolerances object.
  2. Modify the object’s m_distance_display_precision member variable.
  3. Replace the current ON_3dmUnitsAndTolerances with the newly modified one.


The following sample code demonstrates how to change the unit’s display precision of the current document using the Rhino C/C++ SDK…

CRhinoCommand::result CCommandTest::RunCommand( const CRhinoCommandContext& context )
  // Make a copy of the current model units and tolerances
  ON_3dmUnitsAndTolerances units = context.m_doc.Properties().ModelUnitsAndTolerances();

  // Prompt the user to enter a new display precision value
  CRhinoGetInteger gi;
  gi.SetCommandPrompt( L"New display precision" );
  gi.SetDefaultInteger( units.m_distance_display_precision );
  gi.SetLowerLimit( 0 );
  gi.SetUpperLimit( 6 );
  if( gi.CommandResult() == CRhinoCommand::success )
    // The the user's input
    int distance_display_precision = gi.Number();
    if( distance_display_precision != units.m_distance_display_precision )
      units.m_distance_display_precision = distance_display_precision;
      // Replace the current setting with our updated value
      context.m_doc.Properties().SetModelUnitsAndTolerances( units, false );

  return CRhinoCommand::success;