Object-oriented CAD and Parametric 3D Modeling

The term “object-oriented” derives from a computer programming technique in which blocks of code are assembled like Lego pieces into larger components. Java and C++ are examples of object-oriented programming languages. Object-oriented CAD is a new idea for modeling physical objects such as building components. Elements of a building are represented as objects, containing the physical geometry as well as many other kinds of attributes.

Over its first 20 years, CAD was used to automate hand drafting, the creation of 2D drawings such as plans, sections and elevations. Such drawings consisted of lines and shapes without any intelligence about what the lines and shapes represented. A CAD program can draw a window with a fine degree of geometric precision, but it does not know about the window’s energy efficiency or what it costs or how long it takes to install. The idea behind object-oriented CAD is that rich information about building components could be modeled in a form accessible by a wide variety of software applications and used throughout a building’s life cycle without conversion or translation into other formats. Properties including shape, behavior, performance data, and transport requirements, along with embedded links to relevant code requirements and test results, could all be included in an electronic “object.” When an architect adds a door, it will describe not only the physical attributes of the door needed for design by the CAD program, but also the cost, maintenance, supply and installation properties of the door for use in project costing and scheduling, and later for facilities management.

parametric modeling with Revit

Objects combine to form a complete model of a building, with much richer information than the three-dimensional computer models used for design study and presentation. Such geometric models include shapes, lines and points, and three-dimensional components such as blocks, cones and spheres, but do not carry intelligence about other properties of these objects. Other kinds of computer models include parametric, procedural, and generative models.

Parametric models permit the relationship between elements to be seen. When a variable is changed, its effect is seen on related elements. Originally developed for the aerospace and automotive industries for designing complex curved forms, parametric modeling works like a numerical spreadsheet. By storing the relationships between the various elements of the design and treating these relationships like mathematical equations, it allows any element of the model to be changed and automatically regenerates the model in much the same way that a spreadsheet automatically recalculates any numerical changes. As such, it becomes a 'living' model - one that is constantly responsive to change - offering a degree of flexibility and coordination never previously available. The same technology also allows curved surfaces to be rationalized into flat panels, demystifying the structure and building components of highly complex geometric forms, allowing them to be built economically and efficiently. Plans, sections, elevations, finish and door schedules are all generated as views of the model and automatically updated with every change.

natural phenomena such as trees, plants, and mountains can be defined by procedural models. courtesy Technical University of Vienna.

Procedural models add the ability to, for example, prevent incompatible elements from being placed adjacent to each other, or that doors are not swinging in an illegal direction. Generative models create geometries that fulfill requirements entered by the user, such as: “generate the optimal layout of theater seats for this auditorium” or “create a single-run stair between Floors 1 and 2.” Generative models follow rules set by the designer, such as “seat rows shall be 22 inches apart” or “risers shall not exceed 7 inches.”

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