In NX, what must you define as a reference point while mirroring features?

When mirroring features in Siemens NX, defining a datum plane as the reference point is crucial. A datum plane provides a precise and stable surface or plane from which the mirroring operation can be conducted. This ensures that the geometry is accurately mirrored in relation to the defined plane, maintaining the intended symmetry and alignment of the parts.

Using a datum plane is particularly beneficial because it can be established based on the geometry of the model or designated by the user, allowing for flexibility in complex designs. Furthermore, this approach minimizes ambiguity that could arise from using more arbitrary reference points, such as random edges or curves, which may not offer a consistent basis for the mirroring operation.

In contrast, while the center of mass, random edges, and center of curves can be utilized as reference points in certain scenarios, they do not provide the same level of consistency and control as a datum plane, which is specifically designed to serve as a reference in 3D space for various modeling operations, including mirroring.