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In FreeCAD the word "Datum" is normally used to refer to auxiliary geometry in the PartDesign Workbench. These geometrical elements will not form part of the final Shape of the Body, but can be used as references and supports for sketches and other types of features.

The following correspond to elements derived from the Part::Datum class, itself derived from Part Feature:

The following are derived directly from Part Feature:


  1. Switch to the PartDesign Workbench.
  2. Press PartDesign Body.svg PartDesign Body.
  3. Select the Origin of the Body, and make it visible by pressing the Space bar in your keyboard.
  4. Press PartDesign Plane.svg PartDesign Plane to open the plane task panel.
  5. In the 3D view, click on one of the standard planes, for example, the XY plane. Then press OK to close the task panel.
  6. Now in the tree view, select the newly created DatumPlane, and then press PartDesign NewSketch.svg PartDesign NewSketch.
  7. Create a closed wire, and then use PartDesign Pad.svg PartDesign Pad to extrude the sketch, and create an initial solid.

Now you can move and rotate the DatumPlane as you wish, by changing its properties in the property editor, and the Sketch and Pad will follow its new Placement.

You can add other types of datums to be used with other sketches and features.


Since they appeared in v0.17, datum objects were intended to be used inside PartDesign Bodies. However, since they are useful "reference" objects with different attachment methods, it has been proposed that they should be available outside of the PartDesign Workbench. In this way, they will be usable in all workbenches as supporting geometry, particularly in the context of creating assemblies.