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Non-Intrusive
Site Scanning with LIDAR (Light Radar) System
The Need
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Recent studies by the Construction
Industry Institute have indicated that for a typical $100 million construction project,
between $500,000 and $1million is spent on keeping track of where things are on the site
and monitoring the status of construction activity. This indicates that the timely
knowledge of project status -- where things are, what has been done, what needs to be done
-- is the single most important issue facing construction managers today. But the
measurement is required in a construction quicker and cheaper than current practice and
should be done without impacting existing operations. |
Actual lidar scan : This image provides an example of the dense clutter to be expected at
an everyday construction site
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With research managed
by National Institute of Standards and Technology, this can be done by developing
techniques for real-time assessment and documentation in terms of 3D as-built models of
the constructions such as as-is condition of hazardous environment where human
intervention would be impossible. |
The Technology
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Tracking the state of components at
construction sites that are of an amorphous nature such as terrain is currently done by
surveying. This can be costly and time-consuming. The emergence of scanning lasers
has made real-time updates and earthwork calculations of the construction site a viable
technique. The gathering of data is non-intrusive and will not impede the
construction progress.The scanned data are
imported using the import module. A file is then
opened containing x, y, and z data values and stored as a 2-vector (x, y position)
location and a scalar value (z). Modules construct, regrid and rubbersheet
are the primary modules. Construct defines the mesh size and origin. Regrid maps the
scattered points onto a grid. The module allows for the specification of the number of
nearest points to the grid point to be used to calculate the average data value for that
grid point. A radius may also be defined within which the nearest neighbors can be found.
The Module rubbersheet deforms the surface based on the data values (z-values) of the
surface. |
The volumes are computed by multiplying the projected
are of the triangle by the average of the height of the prism and then summing up the
volumes for all the prisms.
Automatically generated cut/fill map created by
operating on the 3D terrain model of above figure. Negative numbers represent fill
requirements (in m) while positive contours represent cut requirements.
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The Benefits
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- Real-time assessment of construction progress;
- Remote monitoring of construction by design engineers, project
manager, architect, etc.;
- Early detection of error in construction procedure resulting
in cost savings;
- Obtaining as-built models of structure;
- Improved project planning and documentation.
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Status
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In the past several months, NIST has shown that
the scanning technology is a viable technique. Calculation of cut/fill requirements
can be done semi-automatically and 3D graphical representations of the terrain can be done
using commercially available software. Currently, registration of point clouds is
done manually. Automatic registration will be further developed in the upcoming
years. |
Barriers
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- Single location scan not sufficient to capture the scene
fully. Scans obtained from several locations are needed to eliminate occluded
objects and features. Automatic registration and a mobile platform have to be
developed.
- Object recognition from point cloud data is needed so that the
object may be removed if necessary or replaced with a more accurate and basic/simple 3D
object.
- Real-time update and accurate scanning lasers (millimeter
level accuracy) are not currently achievable based on current scanning technology.
- Resistance by construction industry to utilize "new"
technology until it has been proven to be reliable and results in cost-savings.
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Points of Contact
- Geraldine S. Cheok, Research Structural Engineer, National
Institute of Standards and Technology, Phone: (301) 975-6074, FAX: (301) 869-6275, E-Mail:cheok@nist.gov
- William C. Stone, Leader, Construction Metrology and
Automation Group, National Institute of Standards and Technology, Phone: (301) 975-6075,
FAX: (301) 869-6275, E-Mail:william.stone@nist.gov
References
- National Institute of Standards and Technology, Gaithersburg,
MD <http://www.nist.org>
- Geraldine S. Cheok and William C. Stone, Non-Intrusive
Scanning Technology for Construction Assessment, Construction Metrology & Automation
Group, National Institute of Standards and Technology.
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. |
SL07 |
