Documents, assemblies and PMI

A Model holds geometry. An ogeom::doc::Document holds the product information around it: parts, the assembly tree, names, colours and annotations. The exchange formats read and write documents, because that is what a STEP file contains.

let mut document = ogeom::doc::Document::over(model);
let bolt = document.add_part("bolt", bolt_shape);

Assemblies

Products form a tree:

• A part is a leaf.
• An assembly places other products as Instances.

Instances share geometry. Two bolts in an assembly point to one shape node under different location chains, so a thousand fasteners are not a thousand copies.

• roots() returns the top-level products.
• occurrences_of(root) flattens the tree into placed Occurrences. Each has a path string and its placed shape.

Attributes and PMI

Colours and named attributes attach to products and to individual faces.

PMI (the dimensions, geometric tolerances and datums of a manufacturing drawing) is stored in two forms:

• Semantic: a dimension knows which faces it measures, through the same stable references used everywhere else.
• Presentation: Callout polylines, the drawn form.

Both forms, and the distinction between them, survive STEP.

Views and notes

• A View is a named camera plus the callouts it shows. Annotated models use views to organise PMI into readable sheets.
• A Note is authored text, optionally attached to a product.

Both survive the native format and STEP.

Undo

The document records every structural change as a step. Undo and redo walk those steps. undo_depth() returns how many steps are available in each direction.