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CIPA 2003 XIX th International Symposium, 30 September - 04 October, 2003, Antalya, Turkey
No further comprehensive surveys were carried out to date,
however many aerial images of specific areas within Dubai are
available.
3. 3D DIGITISATION
The study attempted to create a 3D model of Bastakia area in
order to document an interesting spatial setting by testing
affordable modelling methods and tools that should in principal
allow the production of an acceptable 3D model. This product
can be used by students in order to carry out urban analyses and
develop and evaluate design proposals in this particular area.
There was no budget available for the purpose of this exercise,
apart from the interest of the author and students. Before
embarking on the building of the 3D model there was a need to
review and examine existing 3D digitisation methods and their
suitability to the project.
There are many ways of digitising an object or a building, but
these generally fall into seven categories: mechanical tracking
technology, laser scanners, magnetic tracking, ultrasonic
scanning, Photogrammetry, Interferometry technology, and
optical 3D scanners.
3.1 Mechanical Tracking technology
This uses a mechanical arm that is compact and easy to use.
This device digitises contours of physical models using
software such as Inscribe 3.0 to process the data. The 3D
computer model can then be transferred to a CAD application
such as 3D Studio Max or AutoCAD for further modelling. This
device has been used by students at the UAE University to scan
physical models with relative success due to the fact that the
captured 3D model needs considerable editing.
3.2 Laser Scanning
This is a very quick procedure that scans any physical object. A
3D dense mesh is produced as a result. This technology has
some drawbacks since reflective or transparent surfaces are not
digitised very efficiently. It is also expensive and the processing
of the scanned data can be time consuming.
Laser scanning is being increasingly used to capture 3D models
of real objects and buildings. This technology uses from
airborne to handheld devices depending on the applications and
the budget available.
3.3 Magnetic Tracking
This technology uses a magnetic field as the signal medium.
However, this can be influenced by metal or magnetic fields
that may be present near or in the digitised objects.
3.4 Ultrasonic Scanning
This technology uses sound waves to obtain coordinates in 3D
space. Unfortunately, these scanners are not very accurate and
can be influenced by atmospheric conditions and sound
interference.
For example, the LSC Series incorporates a new ScanView
scanning device. ScanView Plus combines motion and
instrument control with data acquisition to provide unsurpassed
ultrasonic imaging capabilities. Unique ScanView Plus features
include: drag and drop gating, Scan Wizards for fast-guided
setups, and configurable templates for organizing scan and
analysis sequences. Analysis tools include automated
clustering, point and area measurements, and a variety of image
enhancement and signal processing utilities.
3.5 Photogrammetry
Photogrammetry means “the process by which accurate
dimensions and 3D CAD-compatible models are extrapolated
from stereoscopic photographs”.
A number of photographs of physical models are digitised in
three-dimensions to obtain a computer surface model that can
be exported to any CAD application for further analysis. Its
application is very attractive to architectural conservation, and
recreation of built environments.
True Orthophotography is an efficient method to represent
“photographic information in a 2D reference system”, but its
application in complex situation involving uneven objects such
as buildings is problematic. The generation of accurate Digital
Surface Model - DSM is complex and time consuming and
requires sophisticated equipments such as laser scanners, in fact
“the generation of a DSM cannot be automated”. (Boccardo, P.,
2002: 1) Several methods are used in conjunction to produce
true orthophoto by means of using DSMs. (Amhar, F. et al,
1996). Simpler approaches have been developed using the
latest technology in data capture, e.g. laser scanning, in addition
to the development of software capable of accurately processing
the data and generating true orthophoto. (Boccardo, P., 2002)
3.6 3D Camera series: Hi-speed/accuracy non-contact 3D
measuring machine
The Handy Handheld Digitiser combines a sophisticated digital
camera and the proprietary EOIS Moire Interferometry
technology to create a totally wireless 3D digitiser. It is the only
high-speed 3D digitiser that can capture data without being
connected to a computer. The images are stored in a
sophisticated digital camera, and later sent to a computer for
final processing.
The primary EOIS product is the Mini-Moiré sensor. It is based
on the original EOIS Moiré technology, for high-speed 3D
XYZ measurement. This technology has a much higher data
acquisition speed and point density than conventional touch
probes or laser sensors.
3.7 DigiScan Optical 3D Digitizers
Being pushed by the availability of high speed and high
precision image processing components, optical 3D scanners
continue to find their places in an increasing number of
demanding applications.
The measurement principle is based on a modification of the
well-known structured light method. In many application fields
there is a growing need for 3D replica of physical objects that
cannot be created in traditional CAD. Numerous examples can
be found in product design and presentation, manufacturing
automation, and quality control.
New and attractive applications coming up are in medical and
anthropometric measurement (scanning human body parts or
