BIM versus Documenting Complex
Geometry: A Battle That Can Be Won
Marcin Klocek – University of Hong Kong, DOT Architects Ltd.
AB4465
The class will start from describing the problems architects may still face when trying to model and
document buildings of complex geometry, despite recent great improvements in Autodesk® Revit®
modelling capabilities. Then I will discuss the strategy of modelling and collaboration between an
External Modelling Application (EMA) and Autodesk® Revit® developed for the Entrance Building of
the West Kowloon Terminus in Hong Kong. It will be presented together with a purpose built family
and programs, written in C# and the Autodesk® Revit® API environment, which helped to optimize
and model the cladding of a complex, organic surface. Among the reasons for such approach was the
need of optimizing the design for production, limitations of out-of-the-box Revit, but also lack of
industry and legal procedures for adopting BIM models as contracted parts of project documentation. I
will initiate a discussion with the audience about ways to improve the situation in both areas.
Learning Objectives
At the end of this class, you will be able to:






Describe possible problems with modelling and documenting cladding of complex surfaces
and general ideas to solve them.
Understand the mechanism of standardizing cladding panels by post-processing data from
External Modeling Application (EMA) – in this case Rhino.
Design a panel family, which can control its location in space by type parameters.
Use Autodesk® Revit® API to load such a family and batch-create a large number
(thousands) of its instances in the project.
Use Autodesk® Revit® Type Catalog mechanism to automatically create family types.
Use schedules to visualize groups of standardized cladding panels in the model.
About the Speaker:
Having studied both architecture and computer programming, Marcin is a devoted BIM enthusiast
since 1996 (long before the Autodesk® Revit® era). He now teaches BIM technology and Autodesk®
Revit® at the Faculty of Architecture of the Hong Kong University. He is also a BIM consultant for
Aedas Ltd. working on the company-wide Autodesk® Revit® standards. Having worked over recent
years on some of the most complex and challenging projects in Hong Kong and Asia, he combines
hands on architectural office practice, teaching, and academic research—a creative mixture which
explodes from time to time with cool ideas.
Email: marcin.klocek@dot-architects.com
BIM Versus Documenting Complex Geometry: A Battle That Can Be Won
Introduction
Increasingly complex forms of buildings, which are being designed in recent years demand from
architects solutions to new problems related to rationalization, cost optimization and documentation of
such structures. Finding these solutions often requires a multidisciplinary approach as they may
combine issues of design, technology, mathematics, programming and data management. BIM is the
obvious tool to be used in such cases, but even in this area collaboration between different software
platforms may be necessary to do the job.
The ideas and procedures presented here are aimed to offer a general solution, which could be
applied in any similar case. They were however developed and tested while working on one of the
most spectacular and complex projects recently designed in Hong Kong – the Entrance Building of
the West Kowloon Terminus – the main railway station for the trains from and to China, now under
construction. Therefore the sample forms and models, used here for demonstration and explanation
of the workflow come from this project. The building was designed by Andrew Bromberg of Aedas Ltd.
and all the images used in this presentation are courtesy of Aedas Ltd, unless otherwise stated.
Entrance Building of the West Kowloon Terminus in Hong Kong
The main structural elements of the roof of the WKT Entrance Building are four huge steel trusses of
a triangular section 12x6m and lengths from 150 to 200m. For the purpose of this class we will use
one of them as a sample.
Typical section of a V-truss of the WKT Entrance Building
2
BIM Versus Documenting Complex Geometry: A Battle That Can Be Won
Main structural elements of WKT Entrance Building isolated in an Autodesk® Revit® model
Target:
To model and document a complex, organic building surface clad with rectangular panels.
Problems and Solutions:
Problem 1 - Performance
Frequent updating of the geometry driven by complex parametric relationships is needed in
conceptual design stage. Some parametric constraints are too complex to be set in Autodesk®
Revit® and the size of the model is too big for the computers to handle changes in real time.
3
BIM Versus Documenting Complex Geometry: A Battle That Can Be Won
Solution
An external parametric modelling application is used at the beginning of the project. Data will
have to be transferred to Autodesk® Revit®.
Conceptual
model
Model for
documentation
in EMA
in REVIT
Problem 2 - Standardization
Cost issues with too many unique cladding panels resulting from design driven, theoretical
panelization of the geometry.
Solution
Process data (coordinates of panels) from EMA by a purpose written program, which optimizes,
standardizes and groups panels of similar sizes.
Conceptual
model
in EMA
External
optimization
program
Model for
documentation
in REVIT
Problem 3 - Coordination
Need for precise and automated coordination between complex model and documentation in
further stages of design (schematic, detailed) with geometry still changing occasionally.
Solution
Use Autodesk® Revit® in all subsequent design stages as the main tool for modelling and
documentation of the project based on the optimised data from EMA.
Conceptual
model
Model for
documentation
in EMA
in REVIT
Documentation
Problem 4 - Scheduling
Architect’s responsibility to deliver correct and properly formatted numerical data to the client and
quantity surveyors.
Solution
a. To designate the Autodesk® Revit® model a part of formal contractual documentation, so that
all the necessary data can be extracted by the consultants dynamically as needed using
Autodesk® Revit® tags and schedules.
b. To create and format schedules of cladding panels in Autodesk® Revit® and include them in
the deliverables as static documents.
4
BIM Versus Documenting Complex Geometry: A Battle That Can Be Won
Implementation
1. Strategy for transferring data between EMA and Autodesk® Revit®
When modelling needs to be done in two applications simultaneously, a perfect coordination
strategy has to be developed to ensure that both models remain identical.
1.1. Synchronizing the zero point of the coordinate system in EMA and Autodesk® Revit®
1.1.1. A site boundary is set up in Autodesk® Revit® using coordinates supplied by the client
in an Excel (.csv) file.
1.1.2. A reference CAD file with grid system set out over the site boundaries is imported into
Autodesk® Revit® and aligned with the site boundary created in the previous step.
1.1.3. An intersection of two grid lines is selected as a zero point of a local coordinate
system, which will be used for exporting data from EMA. A Project Base Point is
moved to this intersection in Autodesk® Revit®.
1.1.4. The same point (relatively to the site boundary) is set in EMA as a zero point of a
coordinate system.
1.1.5. An Autodesk® Revit® file prepared according to the above steps is saved as a
template file Location.rte to be used for testing and final project file.
1.1.6. This procedure ensures that every object created in Autodesk® Revit® with
coordinates from EMA will be located in both models at exactly the same place in
space in relation to the site boundary and grid.
1.2. Building Autodesk® Revit® panel family controlled by the data from EMA
1.2.1. Panel family uses coordinates from EMA as its parameters.
1.2.2. Parameters control the location of family instance in space.
1.2.3. Values of family parameters are set by Autodesk® Revit® Type Catalog mechanism.
1.3. Using API to automate creation of Autodesk® Revit® objects with data from EMA
1.3.1. Streams of numbers from EMA (coordinates of four corners of panels) are formatted in
Excel as .txt files readable for Autodesk® Revit® Type Catalog mechanism.
1.3.2. A purpose written API script loads the panel family with types defined in the .txt file
(using Type Catalog mechanism) and batch-creates every panel at the correct location
in space.
2. Optimization of panels to maximize standardization
Divisions of the architectural form with theoretical lines for the purpose of cladding are modelled in
EMA. Due to the varying curvature of the surface being divided the resulting panels are all slightly
different from each other. Production of many thousand (around 30000 in this case) unique
aluminium panels roughly 1500x2000 mm in size would be very costly and troublesome, so some
optimization strategy has to be introduced.
2.1. Principles of optimization strategy
2.1.1. Panels, which are similar, are grouped together and replaced by an identical panel of
the size, which is an average of all the sizes of panels in a group.
2.1.2. As a result of the panel replacement, edges of the neighbouring panels are no more
parallel i.e. gaps between panels do not have a constant width. This is visually
acceptable as long as the change of width will not be noticed by an average observer.
It is achieved by constraining the width of gap to a predefined range (20-40mm).
2.1.3. Panels are considered “similar” when their theoretical sizes (calculated from EMA
coordinates) differ only so much that the resulting gap between panels stays within the
predefined range described above.
5
BIM Versus Documenting Complex Geometry: A Battle That Can Be Won
2.2. Implementation of optimization strategy
2.2.1. The data from EMA is processed by an external program PanelOptimizer() before
being used in Autodesk® Revit®.
2.2.2. Based on coordinates from EMA the program finds similar panels, groups them and
calculates the average dimensions of panel for each group.
2.2.3. The calculated data (average panel dimensions and group number) are written to
output file as additional parameters for every panel.
2.2.4. The format of output file is readable by the Autodesk® Revit® Type Catalog
mechanism.
.txt file with
theoretical panel
coordites from
EMA
input
.txt file with
optimised panel
sizes for Revit
optimizing program in C#
output
#C#
3. Building a mass family for cladding panels
To be able to create objects in Autodesk® Revit® based on coordinates from external application
one needs a family, whose location in space can be controlled by its parameters. In this case a
family modelling aluminium panels is a warped quadrilateral with thickness (extruded).
3.1. Controlling the location of four primary driving points of a panel by family parameters.
3.1.1. The family has to be based on conceptual mass family template, because Point
Element objects, which will control four corners of the panel, are only available in
Conceptual Mass Family Environment.
3.1.2. Each of four corner points is hosted by Level 1, and constrained by dimensions to two
default Reference Planes: Center (Left/Right) and Center (Front/Back).
3.1.3. As a result three family parameters (coordinates) can control the location of Point
Element in relation to the default insertion point of the family (intersection of three
default Reference Planes):
 x - Distance from Center (Left/Right) plane.
 y - Distance from Center (Front/Back) plane.
 z - Offset from Level 1 (host).
3.1.4. All four driving points of the panel are therefore controlled by 12 parameters
(coordinates).
3.1.5. Those four points further drive four Reference Lines, which follow the centre lines of
gaps between neighbouring panels.
6
BIM Versus Documenting Complex Geometry: A Battle That Can Be Won
Panel family in conceptual modelling environment
3.2. Controlling gaps between panels.
The above procedure allows controlling four points, which sit at the intersections of centre
lines of gaps between neighbouring panels (called Base Geometry Lines – BGLs). To
account for gaps the location of proper corners of panels has to be driven by further
parameters, which will control the size of those gaps.
3.2.1. Each of four panel driving points - P1 is a centre of a sphere S1, which hosts by
intersection point P2 along Reference Line L1. The radius of this sphere controls the
location of point P2 along this Reference Line L1.
3.2.2. Point P2 is a centre of sphere S2, which controls the location of point P3 along
Reference Line L2. As a result distance P1P2 (radius of sphere S1) controls gap G1,
distance P2P3 (radius of sphere S2) controls gap G2.
Elements parametrically dependent on the panel’s driving point P1
7
BIM Versus Documenting Complex Geometry: A Battle That Can Be Won
4. Creating panels in Autodesk® Revit® based on optimised data
After the panel sizes from EMA are optimised and properly formatted as .txt files, the panels are
created in Autodesk® Revit® using an API macro, a purpose built panel family and Type Catalog
mechanism.
4.1. How the API macro works?
4.1.1. An Autodesk® Revit® project file is created from a template Location.rte to ensure the
compatibility of coordinates with external data.
4.1.2. An API macro PanelMaker from the module PanelFactory is executed as Autodesk®
Revit® Application Macro in the project file using Macro Manager.
4.1.3. The macro begins loading the family Alu_Panel.rfa from a specific location on a hard
drive.
4.1.4. A file Alu_Panel.txt containing data of panels to be created in Revit is in the same
location as Alu_Panel.rfa, so it is automatically used by Revit as a catalog of types for
this family. Every cladding panel is therefore a different type of the Alu_Panel family.
4.1.5. After the family is loaded and all the types are created, the macro generates in the
project one instance of every type of the family – an aluminium cladding panel, which
is immediately correctly positioned in space, its location being controlled by type
parameters.
Conceptual diagram showing the process involving PanelMaker() macro
4.2. Standardization vs. modeling
4.2.1. Family parameter Group, which is passed to panels via .txt file by Type Catalog
mechanism while loading an Alu_Panel.rfa family allows to identify panels, which
should be identical (belong to the same group).
4.2.2. The panels belonging to the same group are NOT actually modeled according to their
standardized dimensions, but to “theoretical” ones (as in EMA, before optimization).
This means that gaps between panels in the model are still of constant width. The
information about standardized size of panel - lengths of four sides and one diagonal,
which is enough to produce it, is recorded only in the panel’s parameters. By making
the panel family and the whole procedure even more complex the “final”
(standardized) shapes of panels and uneven gaps could be modeled, but it would be
time consuming and, above all, unnecessary for the task given.
8
BIM Versus Documenting Complex Geometry: A Battle That Can Be Won
5. Scheduling panels for various purposes
After successful optimization and modelling the panelized surface in Autodesk® Revit®, the
wealth of the data obtained has to be organized and presented in a proper form for the client,
quantity surveyors and manufacturers. It is obviously done with Autodesk® Revit® schedules.
5.1. Schedule of individual panels
This schedule shows individual panels (may have many thousands rows) and allows for
showing panel properties like:
 Individual panel name
Every panel in the model was given a name according to a precise naming system based
on the hierarchy of structural elements and their location in space. Decoding a name like
P2S14P013 allows finding this particular panel in the real building. In the model it is even
easier – it just gets highlighted.
 Coordinates of four driving points
 Finish group name
Apart from sizing groups panels were also assigned a finish group, which defined a set of
finishing properties (colour, texture, etc.)
Schedule of cladding panels in Autodesk® Revit®
5.2. Schedule of sizing groups
This schedule groups panels by the value of Group property and shows:
 Sizing group name
Includes two letter material code of the panel and three digit sequential number of a
group.
 The number of panels in each group.
This is the way to measure the effectiveness of our standardization strategy. The average
number of panels in all groups indicates by how many times the number of unique
cladding panels for the whole building was reduced. In case of the WKT project, for which
this strategy was used, this factor was about 20.
 Group Area
Information about the quantity of material (not including losses) needed for producing
panels of given type (size and shape).
 Dimensions of standardized panel
Four edges and one diagonal, which uniquely define the geometry of a quadrilateral panel
for manufacturer.
9
BIM Versus Documenting Complex Geometry: A Battle That Can Be Won
As every row of this schedule describes all the panels belonging to a given group,
highlighting this row in a schedule highlights all the relevant panels in the model. This is the
way to visually identify identical panels in the model.
Schedule of panel groups in Autodesk® Revit®
Panels of a sizing group A8 highlighted in an Autodesk® Revit® model
10