77 research outputs found
Reconstruction of industrial piping installations from laser point clouds using profiling techniques
Includes abstract.Includes bibliographical references (leaves 143-152).As-built models of industrial piping installations are essential for planning applications in industry. Laser scanning has emerged as the preferred data acquisition method of as built information for creating these three dimensional (3D) models. The product of the scanning process is a cloud of points representing scanned surfaces. From this point cloud, 3D models of the surfaces are reconstructed. Most surfaces are of piping elements e.g. straight pipes, t-junctions, elbows, spheres. The automatic detection of these piping elements in point clouds has the greatest impact on the reconstructed model. Various algorithms have been proposed for detecting piping elements in point clouds. However, most algorithms detect cylinders (straight pipes) and planes which make up a small percentage of piping elements found in industrial installations. In addition, these algorithms do not allow for deformation detection in pipes. Therefore, the work in this research is aimed at the detection of piping elements (straight pipes, elbows, t-junctions and flange) in point clouds including deformation detection
Plane Segmentation and Registration of Sparse and Heterogeneous Mobile Laser Scanning Point Clouds
This research discussed and analysed the limitations of different state of the art methods for point cloud processing tasks due to the sparseness and the heterogeneousness of the MLS point clouds. A novel plane detection and segmentation method for sparse MLS point clouds is proposed. Finally, the most suitable techniques for automatic registration of MLS sparse point clouds were determined based on a new error metric for evaluation
A Concept For Surface Reconstruction From Digitised Data
Reverse engineering and in particular the reconstruction of surfaces from digitized
data is an important task in industry. With the development of new digitizing technologies
such as laser or photogrammetry, real objects can be measured or digitized
quickly and cost effectively. The result of the digitizing process is a set of discrete
3D sample points. These sample points have to be converted into a mathematical,
continuous surface description, which can be further processed in different computer
applications. The main goal of this work is to develop a concept for such a computer
aided surface generation tool, that supports the new scanning technologies and meets
the requirements in industry towards such a product.
Therefore first, the requirements to be met by a surface reconstruction tool are
determined. This marketing study has been done by analysing different departments
of several companies. As a result, a catalogue of requirements is developed. The
number of tasks and applications shows the importance of a fast and precise computer
aided reconstruction tool in industry. The main result from the analysis is, that
many important applications such as stereolithographie, copy milling etc. are based
on triangular meshes or they are able to handle these polygonal surfaces.
Secondly the digitizer, currently available on the market and used in industry are
analysed. Any scanning system has its strength and weaknesses. A typical problem
in digitizing is, that some areas of a model cannot be digitized due to occlusion or
obstruction. The systems are also different in terms of accuracy, flexibility etc. The
analysis of the systems leads to a second catalogue of requirements and tasks, which
have to be solved in order to provide a complete and effective software tool. The analysis
also shows, that the reconstruction problem cannot be solved fully automatically
due to many limitations of the scanning technologies.
Based on the two requirements, a concept for a software tool in order to process digitized data is developed and presented. The concept is restricted to the generation
of polygonal surfaces. It combines automatic processes, such as the generation of
triangular meshes from digitized data, as well as user interactive tools such as the
reconstruction of sharp corners or the compensation of the scanning probe radius in
tactile measured data.
The most difficult problem in this reconstruction process is the automatic generation
of a surface from discrete measured sample points. Hence, an algorithm for
generating triangular meshes from digitized data has been developed. The algorithm
is based on the principle of multiple view combination. The proposed approach is able
to handle large numbers of data points (examples with up to 20 million data points
were processed). Two pre-processing algorithm for triangle decimation and surface
smoothing are also presented and part of the mesh generation process. Several practical
examples, which show the effectiveness, robustness and reliability of the algorithm
are presented
Robust surface modelling of visual hull from multiple silhouettes
Reconstructing depth information from images is one of the actively researched themes
in computer vision and its application involves most vision research areas from object
recognition to realistic visualisation. Amongst other useful vision-based reconstruction
techniques, this thesis extensively investigates the visual hull (VH) concept for volume
approximation and its robust surface modelling when various views of an object are
available. Assuming that multiple images are captured from a circular motion, projection
matrices are generally parameterised in terms of a rotation angle from a reference position
in order to facilitate the multi-camera calibration. However, this assumption is often
violated in practice, i.e., a pure rotation in a planar motion with accurate rotation angle
is hardly realisable. To address this problem, at first, this thesis proposes a calibration
method associated with the approximate circular motion.
With these modified projection matrices, a resulting VH is represented by a hierarchical
tree structure of voxels from which surfaces are extracted by the Marching
cubes (MC) algorithm. However, the surfaces may have unexpected artefacts caused by
a coarser volume reconstruction, the topological ambiguity of the MC algorithm, and
imperfect image processing or calibration result. To avoid this sensitivity, this thesis
proposes a robust surface construction algorithm which initially classifies local convex
regions from imperfect MC vertices and then aggregates local surfaces constructed by the
3D convex hull algorithm. Furthermore, this thesis also explores the use of wide baseline
images to refine a coarse VH using an affine invariant region descriptor. This improves
the quality of VH when a small number of initial views is given.
In conclusion, the proposed methods achieve a 3D model with enhanced accuracy.
Also, robust surface modelling is retained when silhouette images are degraded by
practical noise
Robust surface modelling of visual hull from multiple silhouettes
Reconstructing depth information from images is one of the actively researched themes
in computer vision and its application involves most vision research areas from object
recognition to realistic visualisation. Amongst other useful vision-based reconstruction
techniques, this thesis extensively investigates the visual hull (VH) concept for volume
approximation and its robust surface modelling when various views of an object are
available. Assuming that multiple images are captured from a circular motion, projection
matrices are generally parameterised in terms of a rotation angle from a reference position
in order to facilitate the multi-camera calibration. However, this assumption is often
violated in practice, i.e., a pure rotation in a planar motion with accurate rotation angle
is hardly realisable. To address this problem, at first, this thesis proposes a calibration
method associated with the approximate circular motion.
With these modified projection matrices, a resulting VH is represented by a hierarchical
tree structure of voxels from which surfaces are extracted by the Marching
cubes (MC) algorithm. However, the surfaces may have unexpected artefacts caused by
a coarser volume reconstruction, the topological ambiguity of the MC algorithm, and
imperfect image processing or calibration result. To avoid this sensitivity, this thesis
proposes a robust surface construction algorithm which initially classifies local convex
regions from imperfect MC vertices and then aggregates local surfaces constructed by the
3D convex hull algorithm. Furthermore, this thesis also explores the use of wide baseline
images to refine a coarse VH using an affine invariant region descriptor. This improves
the quality of VH when a small number of initial views is given.
In conclusion, the proposed methods achieve a 3D model with enhanced accuracy.
Also, robust surface modelling is retained when silhouette images are degraded by
practical noise
Non contact surface metrology in a hazardous environment
The EFDA-JET tokamak is an experimental fusion device researching fusion as a means
of energy production. Inside the toroidal vessel, plasma with temperature in excess of
100 million degrees Celsius is generated and constrained by high power magnetic fields.
Additional protection is provided by tiles which clad the inside of the machine. As part
of a major upgrade existing heat protective tiles are to be replaced with an advanced
design, and renewed interest has been shown in dimensional measurement of the
surface.
Measurement must occur during shutdown periods where temperature and pressure are
at ambient levels. Manned entry is not permissible and all work should be performed
remotely. To avoid contamination which could affect the fusion reaction and
experimental results, contact with the measurement surface is not permitted.
This work assesses non-contact surface measurement technologies, along with standards
and guidelines for dimensional surface measurement. Existing measurement test
artefacts do not offer the required surface finish and features, so specific test artefacts
have been designed and produced. These artefacts are traceable to the national length
standard, as traceability is a pre-requisite to evaluate accuracy.
Exploratory tests highlighted two technologies for further investigation, laser
triangulation and white light fringe projection. Two commercially available, state-ofthe-
art examples of each technology have been evaluated using a processing method
developed to highlight performance in key areas relevant to EFDA-JET. These areas
include quantitative assessments of the effect of surface angle on measurement quality,
the effect of depth of field for fringe projection systems and the ability of technologies
to record gap and flush from tens of micrometres to millimetres.
Tests enable a user to begin to assess the impact the measurement system has on the
measurement result, how different technologies and systems used alone or in
combination may resolve or compound erroneous results, clarifying or disrupting the
meaning of results
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An automated method mapping parametric features between computer aided design software
This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonEnterprise efficiency is limited by data exchange. A product designer might specify the geometry of a product with a Computer Aided Design program, an engineer might re-use that geometry data to calculate physical properties of the product using a Finite Element Analysis program. These different domains place different requirements on the product representation. Representations of product data required for different tasks is dependent on the vendor software associated with those tasks, sharing data between different vendor programs is limited by incompatibility of the vendor formats used. In the case of Computer Aided Design where the virtual form of an object is modelled, no standard data format captures complete model data. Common data standards transfer model surface geometry without capturing the topological elements from which these geometries are constructed. There are prescriptive data representations to allow these features to be specified in a neutral format, but little incentive for vendors to adopt these schemes. Recent efforts instead focus on identifying similar feature elements between different vendor CAD programs, however this approach relies on onerous manual identification requiring frequent revision.
This research develops methods to automate the task of mapping relationships between different data format representations. Two independent matching techniques identify similar CAD feature functions between heterogeneous programs. Text similarity and object geometry matching techniques are combined to match the data formats associated with CAD programs. An efficient search for matching function parameters is performed using a genetic algorithm that incorporates semantic data matching and geometry data matching. A greedy semantic matching algorithm is developed that compares with the Doc2vec short text matching technique over the API dataset tested. A SVD geometric surface registration technique is developed that requires fewer calculations than an equivalent Iterative Closest Point method
Real-time simulation and visualisation of cloth using edge-based adaptive meshes
Real-time rendering and the animation of realistic virtual environments and characters
has progressed at a great pace, following advances in computer graphics hardware
in the last decade. The role of cloth simulation is becoming ever more important in
the quest to improve the realism of virtual environments.
The real-time simulation of cloth and clothing is important for many applications
such as virtual reality, crowd simulation, games and software for online clothes shopping.
A large number of polygons are necessary to depict the highly
exible nature of
cloth with wrinkling and frequent changes in its curvature. In combination with the
physical calculations which model the deformations, the effort required to simulate
cloth in detail is very computationally expensive resulting in much diffculty for its
realistic simulation at interactive frame rates. Real-time cloth simulations can lack
quality and realism compared to their offline counterparts, since coarse meshes must
often be employed for performance reasons.
The focus of this thesis is to develop techniques to allow the real-time simulation of
realistic cloth and clothing. Adaptive meshes have previously been developed to act as
a bridge between low and high polygon meshes, aiming to adaptively exploit variations
in the shape of the cloth. The mesh complexity is dynamically increased or refined to
balance quality against computational cost during a simulation. A limitation of many
approaches is they do not often consider the decimation or coarsening of previously
refined areas, or otherwise are not fast enough for real-time applications.
A novel edge-based adaptive mesh is developed for the fast incremental refinement
and coarsening of a triangular mesh. A mass-spring network is integrated into
the mesh permitting the real-time adaptive simulation of cloth, and techniques are
developed for the simulation of clothing on an animated character
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