5,137 research outputs found
Digital representation of historical globes : methods to make 3D and pseudo-3D models of sixteenth century Mercator globes
In this paper, the construction of digital representations of a terrestrial and celestial globe will be discussed. Virtual digital (3D) models play an important role in recent research and publications on cultural heritage. The globes discussed in this paper were made by Gerardus Mercator (1512-1594) in 1541 and 1551. Four techniques for the digital representation are discussed and analysed, all using high-resolution photographs of the globes. These photographs were taken under studio conditions in order to get equal lighting and to avoid unwanted light spots. These lighting conditions are important, since the globes have a highly reflective varnish covering. Processing these images using structure from motion, georeferencing of separate scenes and the combination of the photographs with terrestrial laser scanning data results in true 3D representations of the globes. Besides, pseudo-3D models of these globes were generated using dynamic imaging, which is an extensively used technique for visualisations over the Internet. The four techniques and the consequent results are compared on geometric and radiometric quality, with a special focus on their usefulness for distribution and visualisation during an exhibition in honour of the five hundredth birthday of Gerardus Mercator
Optical Non-Contact Railway Track Measurement with Static Terrestrial Laser Scanning to Better than 1.5mm RMS
The railway industry requires track to be monitored for a variety of reasons, particularly when
any type of physical works take place within the vicinity of the asset (e.g. demolition,
construction and redevelopment works). Terrestrial laser scanning (TLS) has considerable
potential as a survey method for rail measurement due to its non-contact nature and
independence from physical targeting at track level. The consensus from recently published
work using static terrestrial laser scanning is that rail measurements to the order of 3mm RMS
are routinely possible. Such measures are appropriate for extracting the gauge, cant and twist
parameters required by the rail industry, however engineering specifications designed to
ensure safe and comfortable running of the trains ideally require measurements of better
quality.
This paper utilises standard design rail profiles from the UK industry to optimise the way in
which TLS point cloud data are fitted to the rail geometry. The work is based on the use of off
the shelf phase-based TLS systems each capable of delivering single point measurements of
the order of 5mm to cooperative surfaces. The paper describes a workflow which focuses the
fitting process onto discrete planar rail elements derived from the design rail geometry. The
planar fitting process is improved through understanding how data from these scanners
respond to rail surfaces. Of particular importance is the removal of noisy data from the shiny
running surfaces.
Results from a sequence of multi-station TLS surveys of the same set of double tracks taken
from platform level highlight the capability to obtain fits to the rail model of better than
1.5mm RMS. Whilst fitting can be carried out on a single side of a rail, the paper highlights the challenge of obtaining an accurate TLS registration necessary to extract both sides of each rail to the same level of accuracy. This configuration is proven over inter-TLS instrument separations of the order of 30m and demonstrates the TLS network coverage necessary to
achieve such results even in the presence of an occluding electric third rail
As-Built 3D Heritage City Modelling to Support Numerical Structural Analysis: Application to the Assessment of an Archaeological Remain
Terrestrial laser scanning is a widely used technology to digitise archaeological, architectural
and cultural heritage. This allows for modelling the assets’ real condition in comparison with
traditional data acquisition methods. This paper, based on the case study of the basilica in the Baelo
Claudia archaeological ensemble (Tarifa, Spain), justifies the need of accurate heritage modelling
against excessively simplified approaches in order to support structural safety analysis. To do this,
after validating the 3Dmeshing process frompoint cloud data, the semi-automatic digital reconstitution
of the basilica columns is performed. Next, a geometric analysis is conducted to calculate the structural
alterations of the columns. In order to determine the structural performance, focusing both on the
accuracy and suitability of the geometric models, static and modal analyses are carried out by means of
the finite element method (FEM) on three different models for the most unfavourable column in terms
of structural damage: (1) as-built (2) simplified and (3) ideal model without deformations. Finally,
the outcomes show that the as-built modelling enhances the conservation status analysis of the 3D
heritage city (in terms of realistic compliance factor values), although further automation still needs to
be implemented in the modelling process
- …