BIM-Based Parametric Modeling: More on Families and Parameters Building Information Modeling BIM-Based Parametric Modeling: More on Families and Parameters “If they can build airplanes paperless, I think buildings can be built paperless,” Mr. Gehry said. Alec Appelbaum, “Frank Gehry’s Software Keeps Buildings on Budget,” The New York Times, February 11, 2009, sec. Business, http://www.nytimes.com/2009/02/11/business/11gehry.html?_r=1. Slides are made based on Autodesk BIM Curriculum, Greenwold, S., and D. Driver. (2007), Building Information Modeling with Revit Architecture: Lecture Notes, Autodesk, Inc., with additional content created by Wei Yan, Texas A&M University. Image courtesy of: Ryder Architecture Limited

Equation X2 + y2 = a2

can be parametrized by using a free parameter t, and setting Parametric Equation X2 + y2 = a2 can be parametrized by using a free parameter t, and setting x = a * cos(t) y = a * sin(t) Pythagorean theorem In mathematics, parametric equation is a method of defining a relation using parameters. http://en.wikipedia.org/wiki/Parametric_equation

Parametric Equation x = a * cos(t) y = a * sin(t) z = b * t Helix or spiral What is this visually?

Parametric Equation x = a * cos(t) y = a * sin(t) z = b * t Helix or spiral

3D Parametric Design The Marina Bayfront Pedestrian Bridge in Singapore Bentley generative design software, GenerativeComponents (GC). (http://www.aecmag.com/index.php?option=com_content&task=view&id=228&Itemid=37) http://autodesk-revit.blogspot.com/2009/09/williams-parametric-bridge-recipe.html

3D Parametric Design NBBJ: Parametric Strategies in the Design of Hangzhou Stadium (Part 1), by Nathan Miller http://nmillerarch.blogspot.com/search/label/Hangzhou Grasshopper was used

Parametric modeling applications Revit Bentley GenerativeComponents Graphisoft ArchiCad Digital Project Vectorworks Rhino with Grasshopper3D

Parametric modeling applications Sample: Mass length and width controlled by parameter t (simple and complex with conditions)

Objects - Behavior Object category determines: how is the object added, modified, displayed—as well as how it relates to other objects. Objects of the same category share some common behavior, e.g. a curtain wall and a brick wall both are added in a similar manner. They both can establish room boundaries. Some behavior is also influenced by family settings. A component family can anchor to a wall, ceiling, or floor.

Objects - Properties and Parameters Object properties are presented by the parameters held either by instance or type. We modify an object by changing the parameters, e.g. length, material, etc.

Property (Data) Types (not family types) The values of the parameters have types that indicate what kind of values they can contain. Parameter values include numbers, positions in space, strings of characters, and even other objects. For example, a wall’s “unconnected height” is a distance parameter, whereas its “base constraint” refers to a level object. So the “base constraint” parameter is really a parameter of type “level.” So two types of object parameters exist.

Property Types - Primitive Versus Complex Primitive types of parametric values: numbers, lengths, and raw locations. These types cannot be instantiated directly into a model. There is no way to place down a “2” into the second floor of a house. You can type them in or read them off a model by means of dimensions. Complex-typed parameters take values of full objects. These parameters usually reference a specific object in a model, such as a “level”. Therefore the objects of reference must exist before you set the parameter. And then once you have attached a complex property to a model object, that relationship remains invariant unless you change it. Strong typed

Default Values Some of the parameters of an object are specified by the action you take to add it to the model. For example, a wall has its start and end points specified this way. Other parameters are given default values in the object’s family or type, and software developers should make these defaults reasonable. A wall takes the height of the level as its default height. That way it extends from floor to floor by default.

Instance Versus Type Parameters (not parameter’s data type) Every object has a type and is an instance of that type. Type parameters provide the leverage to change many individual instances at once. For example, the door width as a type parameter will affect all doors of that type. This is indeed the default characteristic of most of the doors provided with the software. Otherwise each door object would maintain its own copy of that parameter and could be changed separately.

Instance Versus Type Parameters (cont.) Some parameters, however, make sense only as instance parameters. E.g. the sill height of a window allow flexibility: you could place this type of window at different heights. Type parameters define all that is common between individual instances of the type, and instance parameters define all that can vary from instance to instance (such as placement).

Explicit parameter change The height of a wall as an example parameter appears in a list of properties for the wall. This is its unconnected height. You can type a new value into this field and the wall changes height. This is an explicit parameter change.

Implicit parameter change A good example of this kind of purely implicit parameter is a sketch parameter. A floor is defined by several parameters that determine its composition, thickness, and level. But it also needs to conform to a shape by sketch. A sketch is not a floor. A floor has a sketch parameter, which defines its outline. There is no convenient way to describe a sketch in a property list, so it never appears in them. But it is a parameter, just like wall height.