When you sketch a section in Sketcher, the orientation reference determines the orientation of the sketch in the 2D environment. The orientation reference is used to define the horizontal and vertical constraints in the Sketcher environment.

When you select a sketching plane, the datum plane that is normal to the sketching plane is automatically selected as the default orientation reference. If such a datum plane does not exist, then the default orientation reference is based on an existing plane or the model default coordinate system.

If you select a sketching plane and the orientation reference is not selected automatically, then the sketching plane is oriented by projecting the X-axis of the default coordinate system onto the sketching plane. If the X-axis is normal to the sketching plane, then the Y-axis is projected onto the sketching plane. The projection of the axis on the sketching plane is in the horizontal direction and points to the right.

After you accept this automatically created orientation reference and proceed with sketch creation, you are prompted to select the dimensioning references irrespective of the value of the sketcher_auto_create_refs configuration option.

If you are not satisfied with the automatically created orientation reference, you can change it by selecting a valid orientation reference.