Glossary

Compound

Compound is a shape, that is a collection of shapes called "children". Compounds are like groups in vector drawing programs like Inkscape.

In FreeCAD, a compound is a group of BRep shapes (that is, OpenCascade geometry). Compound is an OpenCascade object itself.

FreeCAD also has Groups, but these merely collect features in model tree into a folder. Objects grouped by a group in FreeCAD, are not treated as one big object; a compound, in contrast, is treated as one object.

Groups can accept any type of FreeCAD objects: geometry, spreadsheets, labels,... whatever you see as an object in a model tree.

Compounds can only contain OCC geometry (including compounds - compounds can be nested), that is, anything that is called "shape". Compound children are not generally displayed in model tree (except the case of an explicitly made compound, Part MakeCompound feature).

Compounds can contain:

• Part primitives, e.g. a Cube. And all geometry that results from Part workbench.
• Sketches
• PartDesign features
• Many of Draft objects: points, lines, beziers, etc
• ...

Compounds can not contain:

• Meshes (unless they were converted to shapes)
• Draft Dimensions and labels (but can contain ShapeStrings)
• spreadsheets
• ...

Compounds are often output by other tools than Part MakeCompound, such as:

• when a solid is Part Cut by some other solid into two or more pieces, the pieces are contained in a compound.
• when a sketch has more than one connected set of non-construction elements, these sets (wires) are compounded.

Lattice workbench uses compounds extensively, as collections of shapes. Populate tools output compounds; ParaSeries pack the results into a compound; Lattice Downgrade packs its output into a compound.

Compounds are not generally shown by FreeCAD as such: there is no way to tell apart a solid cube and a compound of its faces made by Lattice Downgrade by just looking at it. To investigate compounding structure of a shape, there is a special tool, Lattice Inspect.