BIM Resources @ Georgia Tech

The following is a temporary documentation will be revised soon. (Citation from Graphisoft Manual)

At a more detailed level is the question of what are the capabilities of a BIM tool to define new kinds of parametric objects. Most BIM systems have limited parametric modeling capabilities, and these are evolving over time.

1. Can a BIM tool support definition of new parametric objects?
   a. using a Sketch tool, VBA or scripting language, or programming language?

2. Relations within a object:
   a. support for defining geometric relations between points, edges, surfaces
   b. associating parameters with parameters of surfaces or lines
   c. can parameters be non-shape properties? Material strength, surface area, etc.

3. Parameters in one object that refer to another object (like the wall ends ending at another specified wall)?
   a. Object association.
     i. For example, in revit, when the height of wall is changed, the position of a top slop associated that wall are also changed. Thus, it can be one criterion for parametric capability.
   b. Object hierarchy.
     i. For example, When a wall is deleted, windows belongs to the wall also should be deleted. It is also important criteria in parametric capability.

4. Others.
   a. Type of constraints.
     i. Some cad system supports pre-defined constraints only. For instance, parallel, perpendicular, attach and so forth. However, some cad application such as digital project supports some script-language, which include mathematical formula; sin, cos.., equality and inequality sign, in the interface level, not API level.

Parametric capability in ArchiCAD

1. Embedded parametric object

A. These parametric objects are named as "GDL objects" or "Library Parts".

B. These include:
   i. Architectural objects: Wall, Window, Door, Corner Window, Skylight, Lamp and Stair.
   ii. Non-architectural objects: Markers, Labels, Zone and Stamps.

C. GDL objects are made of
   i. 2D symbol
   ii. 3D description
   iii. Additional 2D description
   iv. User interface script.

D. Embedded parametric object is saved as external file or library.
   i. It can be reused for any other project.
   ii. The default setting parameter should be adjusted to fit particular situation by manually.
   iii. Parameter can be a dimension of a certain part of an embedded object, and part or type itself.

2. New parametric object (user-defined parametric object)

A. Without GDL1 :
i. Make 2D shape :
1. By using 2D tools (which has line, arc, fill and hotspots.) can be used to draw electrical symbol, furniture, or personal symbols without scripting.

Q1. How this 2D shape is represented by using parameters?

2. By using existing 2D object.

In this case, the pre-defined parameters are used as parameters of the new shape.

ii. Make 3D shape :
1. Create new parametric object by using embedded objects(slab, wall, column) A. Embedded object can be used to create a parametric model, regardless of their original intended purpose. For example a dining table can be modeled by using columns and slabs. Legs of the table could be tall and thin columns, and the tabletop could be a slab

B. In this case, the parameters used for embedded objects are applied for new objects.

C. However, when a user-defined object is inserted to a project, the parameter of the object should be defined manually. For example, In order to insert a user-defined window, which is made by using slab object, to a hole of window in a wall, the width and height of the window should be inputted manually.

Q: In the case the user-defined window is made by using a window object, the parameters should be inputted manually or not?

B. Without GDL 2.
i. More complex object can be generated through the combination of primitive shape such as cones, cylinder, sphere, curved tubes and vaults.
Q1. How primitive shape is behaved in parametrically. How parametric behavior is defined for the combination of primitive shape?

C. Making Objects with GDL. i. Feature of GDL
   - Because GDL has many 2D and 3D commands, you can make interesting objects that cannot be made with the Tools palette - they can be Complex and Curvy.
   - Because you can define diameters, spacing, thickness, materials and pens, your objects can allow variations -- they can be Parametric.
   - Because you specify elements in a GDL model by precise dimensions, angles or parameters, the objects will be exactly what you want them to be -- they can be Accurate.
   - Because you can write IF statements, you can build rules of behavior into your objects, such as manufacturers' requirements, checks on incorrect parameters, self-sizing components etc. - they can be Smart..    - Because you can write routines that loop around and repeat actions many times, you can economically build large or repetitive structures that would be futile to build with the Tools palette - your objects can be Tools.    - Because you can rotate, slide and resize components in the model, your objects can change their shape - you can make Mechanisms ii. CSG based modeling + Additional solid modeling.    1. If using GDL, look at it in terms of blocks, spheres, cylinders and cones. As your GDL skills grow, you can add prisms, sweeps, plane and meshed surfaces and tubes. iii. GDL dialog box    1. Parameters button.

It shows the list of parameters and parameter titles.

2. Master Script
A. The comment script which is read by the other scripts. It is used reduce the duplication of same script. When the value such as the width of chair seat, it becomes available to all the other scripts. It save user from repeatedly typing the same information into each script. B. 2D symbol.
3. 2D script
4. 2D full view
5. 3D script
6. 3D view
7. Property script.
8. Parameter script
9. comment
10. preview picture
11. user interface script

3. Relations within a object
4. Parameters in one object that refer to another object

A. There is no way for making a relation between parameters in different objects.
B. parameters, used to define one object, can be transferred to the same type of object in order to reduce the setting process while inserting a object.