BIM Resources @ Georgia Tech

Parametric Shape

REVIT creates shapes in either solid form or void form. Solid forms or void forms are created with extrusion, blend (similar to loft with 2 control surfaces), revolve and sweep. REVIT supports two types of Boolean operations, which are join and subtract. Join and Subtract operations keep the originating objects internally (Similar to Ghost in Form Z) and user can un-join or un-subtract later.

As parametric 3D shapes are limited in 4 generation methods and 2 boolean operations, it is difficult to create parametric 3D free form objects in REVIT.
Image below is one of the examples of free form objects in REVIT. REVIT can handle variable height of wall in straight area easily, but cannot handle variable height in curved part of wall.

Parametric object

A Family (parametric object) in REVIT is a collection of objects, which have a common set of parameters, identical use and similar graphical representation. REVIT building provides predefined families, such as, doors, structural members, windows, furniture, and electrical fixtures. For example, a Door object includes geometric parameters and non geometric parameters. Geometric parameters, such as, height, thickness, and width adjust the shape of populated object. Non geometric parameters include fire rating, cost, model, manufacturer and etc.

Control line and objects

Placing object in a REVIT often involves assigning geometric relationships (geometric constraints) between objects. As object constraints can be assigned with the grid line, changes in grid line dynamically are updated to the related object such as wall or column. Constraints between floor and wall update changes of floor height to update wall height, when constraints on wall height and floor height are assigned.

Objects and objects

Location of object is constrained with other objects. When a wall is moved, connected ends of other walls also moves or stretches. Objects belong to other objects can have constraints with the wall. Windows to wall or door to wall relationship provides location of windows in relation with distance from end of wall. Change in wall length, from the side of the related wall, dynamically update location of the wall or door.

Validity of change

The geometric relationship can provides dynamic design validity checking, so that lowering wall height below the door size or putting large door into the wall fire up alert to users and reduce design errors.

Drawings

Drawings are dynamically generated from the model. Updates and revision of the model are reflected.