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Dynamic
Construction Visualizer
The Need
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Discrete-Event
Simulation (DES) is a powerful objective function evaluator that is well
suited for the design of construction operations. Simulation results typically
include the cost and time of construction as well as resource utilization
rates, waiting time and length at queues, etc. The results usually point
out important parts of the operations with potential for improvements that
may result in cost or time savings. Systems such as STROBOSCOPE are currently
available that permit the modeling of construction complex construction
operations in detail. These systems can provide detailed information about
construction operations such as resource utilization, resource idleness,
operation bottlenecks, production rates, and the resulting expected cost
before commencing actual work in the field.
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Notwithstanding these facts, there has been limited use of discrete-event
simulation in planning and analyzing construction operations. Discrete-event
modeling is an inherently complex activity that is both a science and an
art. The modeling of a construction operation requires the description,
in the language of the simulation modeling system, of mental plans that
are often complex and elaborate. Differences between the mental plan and
the operation actually modeled in a first attempt are ubiquitous. Verification
is the process by which the model creator looks at what has been actually
modeled, compares it to what was intended, and updates the model to accurately
reflect the intention.
The developer of the computer simulation model, however, may have misconceptions
about how the actual operation will take place in the field. Thus, a model
may not be an accurate representation of reality despite proper verification
by its developer. Such errors cannot be discovered by verification because
the model indeed reflects what the model creator intended. The aim of Validation
therefore is to determine whether simulation models accurately represent
the real-world system under study. This is typically carried out by consulting
people who are intimately familiar with the operations of the actual system,
but who are not necessarily proficient in simulation.
Simulation models are termed as Credible when the models and their
results are accepted as being valid, and are used as an aid in making decisions.
In the case of both verification and validation, the inner workings of
a model and its output need to be communicated to others for discussion
and input, and in a way that is both comprehensive and comprehendible.
Construction simulation tools typically provide results in the form
of numerical or statistical data. However, they do not illustrate the modeled
operations graphically in 3D. This poses significant difficulty in communicating
the results and workings of simulation models, especially to persons who
are not trained in simulation but are domain experts. Decision makers often
do not have the means, the training and/or the time to verify and validate
simulation models based solely on numerical output. Potential practitioners
are therefore always skeptic about simulation analyses and have little
confidence in their results. This lack of credibility is one of the major
deterrents of the widespread use of simulation as an operations planning
tool in the construction industry.
The design and analysis of construction operations using simulation
makes sense only if the insights gleaned are used in making decisions and
increasing understanding (i.e., they are credible). The lack of credibility
in a simulation model is directly related to the inability to effectively
communicate its results and internal logic. There is clearly a need to
communicate simulated operations in a way that can conspicuously help in
verify, validate, and therefore accredit simulation models. Visualizing
simulated operations can be an effective means of achieving this.
It is a generally accepted fact that visually presented information
is understood and grasped more easily than any other form of communication.
The need to visually communicate simulated operations is more relevant
in the context of construction because construction operations analysts
(e.g., superintendents) typically do not have the necessary training in
simulation to allow them to validate simulation results based on tables
and charts. |
The Technology
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The
Dynamic Construction Visualizer (DCV) is general-purpose 3D visualization
system that allows simulation model developers to animate modeled operations
with chronological and spatial accuracy in 3D virtual space. The system
is independent of any particular simulation-modeling program or CAD modeling
software.
DCV language files unambiguously describe the spatial configuration
of modeled systems with the passage of time. The DCV is as a “post-simulation”
visualization engine that possesses the following characteristics:
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Allows
the user to navigate easily in 3D virtual space and place himself/herself
at any desired vantage point by controlling the camera using the keyboard
or the mouse.
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Allows
the user to jump ahead or back to any desired location in the simulation
by specifying a future or past time value.
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Permits
the viewer to start and pause the animation at any time to make static
observations in the modeled system.
Simulated
operations are visualized in 3D by processing sequential, time-ordered
animation commands written in the DCV language. The animation commands
are contained in an ASCII text file hereinafter referred to as the trace
file. DCV trace files are meant to be generated by simulation software.
Any simulation software capable of writing custom text output during a
simulation run can generate the trace files automatically. These include
most of the programmable generic and special-purpose simulation languages
as well as high-level programming languages such as BASIC, FORTRAN, C and
C++. Non-language based simulation software may also be adapted to generate
trace files during a simulation run.
The DCV uses 3D models of all pertinent resources and system entities
to depict the simulated operations and the evolving product in 3D. The
DCV system does not possess any built-in 3D model building capability.
Instead, required 3D models of system entities can be imported from a wide
variety of 3D CAD modeling software. The DCV provides direct support for
the VRML file format. Geometry files from practically every 3D modeling
program (e.g. AutoCAD™, MicroStation™, 3D Studio™) can be easily exported
or converted into VRML format.
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The Benefits
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Realistic
3D visualization of simulated construction operations can provide valuable
insight about construction operations that are otherwise non-quantifiable
and presentable. Volumes of data that take hours to review can be communicated
in a few seconds. For instance, many techniques are available to simulation
analysts to perform verification (e.g., looking at simulation logs). However,
a visualization of what occurred in the simulation model can reveal such
errors very quickly. Similarly, communicating the working of simulation
models to domain experts through visualization can allow errors in logic
to be easily identified and corrected, and allows planning groups to participate
in discussions aimed at improving the plan.
Operations Level visualization can be potentially utilized
in many ways in construction practice and education. Using available CAD
models of infrastructure and the resources, it can be possible to re-create
in a virtual world what happened in the past (trace-driven simulation)
or what may happen in the future (by showing what was simulated by a simulation
model). These visualizations can be very realistic, with accurate depictions
of construction sites, infrastructure, equipment, and atmospheric conditions
(visibility, fog, rain). Historical (from past data) and predicted (from
simulations) animations can be in compressed or expanded time. A 20 second
incident could be studied in very slow motion. General operations, in contrast,
could be animated in fast motion so that several hours of operations are
viewed in a few minutes.
In general, the value of visualizing construction at
the Operations Level can be tremendous. Being able to visualize construction
sequences and operations can result in tremendous savings in money and
time and help to keep projects on schedule. Visualizing construction operations
in 3D can permit the complete subjective analysis of the construction process.
Construction subtleties such as maneuverability problems at loading and
dumping areas in earthmoving operations, the restricted visibility of the
crane operator in steel girder erection, overcrowding in particular work
zones due to simultaneous execution of different trades in building construction,
and a host of other safety problems such as potential collision between
two machines can easily be deciphered by visualizing the actual construction
operations that lead to the completion of the constructed product.
In addition, 3D Visualization can allow the validation
and verification of operational concepts, enable checking for design interferences
and overall constructability review and the sharing of project information.
It can also enable the testing and validation of construction sequences,
checking for physical clashes of moving pieces and enable communication/coordination
among multiple project participants.
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Status
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The
DCV has been used to visualize several simulated operations both within
and outside the realm of construction. The first figure above presents an animation snapshot
of the main loading area in a modeled earthmoving operation. The alternate
loading area is also visible in the background. In this animation, the
viewer is able to observe the accumulating trucks waiting to be loaded,
the trucks maneuvering to get into position under the excavator, the excavator
digging the earth and loading the trucks until they are full, the trucks
traveling to the dumpsite, accumulating to enter the dump area, backing
up and tipping their load, and then returning to the loading site to begin
another cycle. |
Barriers
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- The application of the technology requires
developing 3D cad models for the process to simulate.
- Some operations are difficult to be
described: the flow of concrete from pump into forms, the deformation of
the terrain as an excavator digs the earth, etc.
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Points of Contact
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Julio
C. Martinez, Assistant Professor, Construction Engineering and Management
Program, Via Department of Civil and Environmental Engineering, Virginia Tech,
Blacksburg, VA 24061-0105. Phone: (540) 231-9420, Fax: (540) 231-7532, E-mail: julio@vt.edu
References
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Kamat V.R. and Martinez J.C. 2000
3D Visualization of Simulated Construction Operations. Proceedings of the
2000 Winter Simulation Conference, 1933-1937
Disclaimer Statement
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Neither the Construction
Industry Institute nor Purdue University in any way endorses this
technology or represents
that the information presented can be relied upon without further investigation. |
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| Last Modified: Monday, 10-Mar-03 11:58:48 EST |
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