Chapter two of the BIM handbook, entitled “Design Tools and
Parametric Modeling”, discusses the evolution of parametric modeling and its
influence on BIM. Parametric modeling can be traced back to the 1960’s when
research in 3D modeling for many different applications really began in
earnest. The major advancement came in 1973 when the ability to create and edit
solid 3D shapes (solid modeling) was developed. There were two approaches in
solid modeling. The first was boundary representation (B-rep) which represented
shapes as closed, oriented sets of bounded surfaces. The other approach was
known as constructive solid geometry (CSG) which represented shapes as a set of
functions that defined the primitive polyhedral. These approaches were
eventually combined, using the CSG representation for editing and the B-rep for
visualizing.
Modeling buildings using 3D solid modeling was developed
around 1980. These applications were good but computationally expensive. A huge
breakthrough was the realization that multiple shapes could share parameters. Eventually
these parameters defining the shapes could be automatically reevaluated,
rebuilding their shape. Current BIM design tools all have their roots in
object-based parametric modeling. Parameters defining one shape can be linked
by rules to the parameters of another shape, allowing for automatic updating of
a design and preservation of relations between objects. In short, parametric
modeling provides a way to create and edit geometry much more efficiently than
the earliest techniques of solid modeling.
Different companies use their knowledge of that specific
industry to define classes of objects and how they are implemented. This
applies to building design, where object families are created specific to the
building design/construction industry, i.e. families of walls, roofs, doors,
etc. Most BIM design software provide the base or essential objects, and allow
the user to go and get additional object families from external sources, i.e.
furniture, electrical equipment, etc. A good application should allow users to
define their own objects. Also, objects need to be assigned properties beyond just
geometry. For example, a room must be assigned expected occupancy, energy
introduced via lighting, etc. rather than just its shape. BIM provides the
opportunity to do this.
Some BIM applications include the capability of modeling
nested assemblies, such as stud framing within a wall. This “part of”
relationship is known as aggregation. Aggregation is important in that it
determines what kinds of rules can be defined between parts. It also allows for
better approximation of material needed, reducing waste and allowing for faster
construction.
Another thing this chapter noted, which I found especially interesting, is that contractual processes and work culture are expected to
continue to center around 2D drawings, whether they’re paper or electronic, for
the foreseeable future. I would have thought that 3D development would be taking over very soon.
Scalability is a common issue in using BIM applications.
Many times the model becomes too large or complicated to run smoothly. Models
exceeding a couple of GB’s are becoming more common. However, recent advancements have
allowed the exchange of only modified objects to combat this issue.
BIM applications are created to do more than just design.
Many of them contain interfaces to other applications for things such as energy
analysis. Following are some BIM terms defined:
- BIM tool – “task-specific application that produces a specific outcome”
- BIM platform - “an application, usually for design, that generates data for multiple uses”
- BIM environment – “the data management of one or more information pipelines that integrate the applications”
There are many BIM platforms out there, including Revit,
Bentley Systems, ArchiCAD, Digital Project, Vectorworks, and Tekla Structures.
These each come with their own advantages and disadvantages. For the sake of brevity
I won’t explain each one but if this is something you’d be interested in this
is a great source for information. I will mention that Revit is the most
popular BIM application in architectural design. It provides an easy-to-use
interface, has a very large set of product libraries, and has the largest set
of associated applications.
In summary, the development of object-based parametric
modeling has been a major catalyst in advancing the building industry from a
drawing-based technology to a computer-based one. However, it is not synonymous
with BIM design tools. BIM utilizes many other tools in designing a building.
Comments
To Ilana Ritvalsky – I think you did a great job in
summarizing the major points about this chapter. I took a lot of the same things
away from this reading but I definitely missed some things. I didn’t realize
that one of the solid modeling methods created shapes by revolutions about an
axis. The only minor critique I would have is that I think they were trying to
make a point that although parametric modeling is integral to BIM, they are not
one and the same, which I don’t think you mentioned.
To Catherine Stephens – I really liked how you summarized
all of the BIM tools’ advantages and disadvantages in one easy to read bulleted
list. I simply pointed out where this information is available but I think
constructing a summary of the major pros/cons of each will be very advantageous
and something I’ll probably save this for future reference.
To Dmitriy Voznyak – This topic of interoperability
is definitely a hot button topic as you said. I have come across this problem
in my research in regards to data passing from different “points” of HVAC
systems. Some companies label a certain point different than another company
which prevents, or at least makes it very difficult to, interpret this data
from building to building. I agree that this will continue in the foreseeable
future, with no company having a monopoly. I’m hopeful that eventually these
companies may be able to be a little more open and begin to standardize some
things while still maintaining some of their “trade secrets”.
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