PMI vs. drawing

PMI (product manufacturing information) embeds dimensions, tolerances and other requirements directly within a 3D CAD model, associated with the specific geometric elements they apply to. A drawing communicates the same kind of requirements, but as a separate 2D (or annotated 3D) document, requiring a person or software to match each annotation back to the corresponding geometry manually.

Why PMI is more directly usable by manufacturing software than a drawing

Software that reasons about a part's requirements, such as feature recognition or manufacturability checks, can use PMI directly since it's already linked to specific geometry, while a drawing-only part requires that same linkage to be reconstructed, either manually or through image/text interpretation.

Where each actually lives

This is precisely the point of comparison; a drawing represents requirements as text and symbols on a page, while PMI represents the same requirements as embedded, geometry-linked data within the 3D model.

Common mistakes

Assuming a 3D model with PMI and a 2D drawing of the same part will always agree perfectly; if one is updated without the other, they can drift out of sync, which is part of the motivation behind model-based definition.

Is PMI a replacement for the drawing?

In a model-based definition approach, yes, PMI in the 3D model can serve as the authoritative source, though many organizations still maintain both.

Can PMI and a drawing disagree?

Yes, if one is updated without the other; this is one of the risks model-based definition and clear revision practices aim to address.

Why is PMI valuable for automation?

Because it's already linked to specific geometric elements, software doesn't need to reconstruct that link the way it would from an unstructured drawing.