Some relations are mandatory and those relations are either added automatically by the program or they are a minimum choice in the Shapes Relation dialog. The mandatory relations that are added automatically are the Base relation for the first shape in a shapes-based project, and the Points Base relation for the first shape in a Points-based project. Then every subsequent shape must have at least one of: a Ground relation (the shape lies on the ground plane), a Coplanar relation (making one face of a shape lie in same plane as another shape’s face), or a Points Base relation to tie the shape to 3D points. These mandatory relations define the basic position of the shape in space. The remaining relations refine the shapes position, orientation or size.
In some circumstances relations can be used to define all the free parameters of a shape so that it will become 3D even without being marked (see also Solving Shapes).
Except for the starting mandatory relations, most relations are added using the Shape Relation Dialog.