A Mirror Body must use what as the mirror reference?

In Siemens NX, when creating a Mirror Body feature, the mirror reference must be a Datum Plane. This is because Datum Planes are specifically designed to serve as references for symmetric operations, making them ideal for mirroring geometry. They provide a flat, defined surface that can be easily understood and used for aligning and reflecting the geometry across a specified centerline.

Using a Datum Plane ensures that the mirrored body maintains symmetry and properly reflects the original geometry across a predefined reference. This is particularly important in design applications where accuracy and alignment are crucial. In contrast, while planar faces, linear edges, and datum axes can be used in various modeling tasks, they do not provide the same level of control and precision when it comes to defining a symmetric operation like mirroring.