About Measurements

Measuring (items, between items, or thicknesses) is usually part of the review process. There are a few things you need to know about measurements.

This page discusses:

See Also
Measuring Items
Customizing Measurements

General Information

Measurements, independently of their type, have a few things in common.

  • You can choose units for measuring various physical quantities in the Preferences dialog box.
  • You can create several measurements, and save them in a markup.
  • You can create the non-persistent measure without removing the existing non-persistent measures.

    To remove the existing measure while creating new measures, you can select the Remove previous non-persistent measure check box available in the app specific preferences. For more information, see Customizing App-specific Preferences.

  • Measurements are not associative. They are not recomputed if the geometry changes.
  • For measures, context menu is not available.
  • A default measurement type is provided based on the selected objects The alternative measurement types and representations are available for selection in the context toolbar during the creation of the measurement. After the measurement is created, only the representation can be changed.

    For more information on measurements that can be created for various combinations of geometries selected, see Reference Information: Multiselection for Measurements.

About Measurement Accuracy

The accuracy of a measurement depends on the accuracy of the underlying geometry (that is, the geometry upon which the measurement is based).

Understanding How Accuracy Works

3D Accuracy (Sag)

The value used to tessellate geometrical data is known 3D accuracy, or sag.

3D accuracy influences the quality of the 3D geometry, and may therefore also influence the accuracy of a measurement.

Exact Geometry vs. Approximate Geometry
Exact geometry contains canonical information (line, circle, plane, cylinder, cone, and sphere), whereas approximate geometry does not contain any canonical information.
Measurement Accuracy

The accuracy of a measurement depends on the 3D accuracy, or on the sag, of the underlying geometry.

If the result is exact, the accuracy value is 0.001mm. If the result is approximate, the accuracy value is twice the sag value.

What You Should Remember

  • A measurement is exact only when all selected geometries are exact. If at least one of the selected geometries is approximate, then the measurement is approximate.
  • Once the measurement is created, you can display the accuracy mode by selecting the measurement and clicking Display More in the context toolbar.

The Specific Case of Measurements Based on Section Curves

When you cut through objects using a section plane, section curves are displayed. When creating measurements based on section curves, you need to keep a few things in mind.

  • Section curves are considered as approximate geometries. Therefore, measurements based on section curves are approximate.
  • Measurement based on section curves are not associative. If you move the section plane, section curves are modified, but measurements are not modified accordingly.
  • You can only create measurements on section curves, not on the cut area enclosed by the section curve.