Commands : MechanicalBrowserOpen , DMUPDATE, DMFIX3D, DMCOINCIDENT3D, DMCONCENTRIC3D, DMPARALLEL3D, DMPERPENDICULAR3D, DMTANGENT3D, DMDISTANCE3D, DMRADIUS3D, DMANGLE3D
Variational Direct Modeling
BricsCAD offers powerful tools for parametric direct solid and surface modeling by using geometric constraints solving (aka variational direct modeling). Solid and surface models can be modified by defining constraints between their elements (edges and faces), as soon as a constraint is added BricsCAD automatically modifies the model and these constraints are updated with subsequent modifications to the model. The key advantage of variational direct modeling is that all constraints are taken into account simultaneously and the model behavior does not depend on the constraints creation order. It allows you to parameterize any feature of the 3D model without worrying about the model creation history.
Dimensional constraints control the dimensions of the model. When such a constraint is introduced or the value of its parameter is changed BricsCAD automatically updates the solid and surface geometry. For example, the dimensions of a box can be controlled by the parameters of three distance constraints applied to the opposite faces.
Constraints can be created using the 3D Constraints toolbar, the Parametric/3D Constraints menu or the Constraints command group in the Quad.
BricsCAD provides the following 3D constraints:

Geometrical constraints: Fix (), Coincident (), Concentric (), Parallel (), Perpendicular (), Tangent (), and Rigid Set ().

Dimensional 3D constraints: Distance () , Radius (), Angle (), Cone Angle ().
Mechanical Browser
The Mechanical Browser () navigates through all the constraints in the model edits dimensional constraints. If you select a constraint in the Mechanical Browser, you can check and edit its properties.
3D Constraints types
The following entities are supported for constraints creation:

Faces of 3D solids and surfaces of planar, cylindrical, spherical, toroidal and conical geometry.

Linear and circular edges of 3D solids and surfaces.

Lines, rayes, xlines, circles and arcs.

Arbitrary curves for Coincident constraint with a point.

Planes, axes and origin points of the world or a block coordinate system.
3D constraints have a number of properties which allow to control how BricsCAD treats them in various situations. For full description see 3D Constraints Properties page.
3D Constraints and Direct Modeling
3D Constraints are taken into account when direct modeling operations are applied. If there is a 3D constraint which fixes the placement of faces or edges this constraint will be preserved during Push/Pull, Move and Rotate operations. The dynamically presented result of the operation respects existing constraints as well. A 3D constraint can be temporary disabled or erased permanently using Mechanical Browser Constraints section.
If some faces or edges disappear in a direct modeling or in a Boolean solid editing operation 3D constraints applied to such entities are removed. However, if there is an exact correspondence between the initial faces and the faces obtained, 3D constraints are automatically applied to new entities.
Depending on the value of the DMRECOGNIZE system variable, BricsCAD automatically recognizes geometrical relations between the surfaces of a solid and preserves them during direct modeling operations (see Design Intent Recognition).