Frank C Langbein

Frank C Langbein
Cardiff University | CU · School of Computer Science and Informatics

PhD Computer Science (Geometric Modelling), Diploma (comparable to MSc) in Mathematics

About

82
Publications
25,700
Reads
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1,709
Citations
Introduction
Frank C Langbein is a senior lecturer in Computer Science at Cardiff University. He received a PhD from Cardiff University in 2003 for a thesis on beautification of reverse engineered geometric models and a diploma (MSc) in mathematics from Stuttgart University in 1998. His research interests lie in the areas of control, machine learning, geometry, simulation and modelling applied to quantum technologies, healthcare, computer-aided design and engineering.
Additional affiliations
August 2017 - present
Cardiff University
Position
  • Professor (Associate)
July 2017 - present
Cardiff University
Position
  • Professor (Associate)
January 2009 - December 2013
RIVIC - One Wales Research Institute for Visual Computing
Position
  • Co-lead of sub-programme on vision-based geometric modelling and the interface with science
Description
  • Point-based modelling, sampling and quantum technologies
Education
October 1999 - June 2003
Cardiff University
Field of study
  • Geometric Modelling
January 1994 - December 1994
Uppsala University
Field of study
  • Mathematics, Computer Science
September 1991 - June 1998
Universität Stuttgart
Field of study
  • Mathematics, Computer Science, Physics, Technical Mechanics

Publications

Publications (82)
Article
Full-text available
We introduce a novel stratified sampling technique for mesh surfaces that gives the user control over sampling density and anisotropy via a tensor field. Our approach is based on sampling space-filling curves mapped onto mesh segments via parametrizations aligned with the tensor field. After a short preprocessing step, samples can be generated in r...
Conference Paper
Full-text available
The authors are developing an automated reverse engineering system for reconstructing the shape of simple mechanical parts. B-rep models are created by fitting surfaces to point clouds obtained by scanning an object using a 3D laser scanner. The resulting models, although valid, are often not suitable for purposes such as redesign because expected...
Conference Paper
Quantum control provides methods to steer the dynamics of quantum systems. The robustness of such controls, in addition to high fidelity, is important for practical applications due to the presence of uncertainties arising from limited knowledge about system and control Hamiltonians, initial state preparation errors, and interactions with the envir...
Preprint
We study the problem of robust performance of quantum systems under structured uncertainties. A specific feature of closed (Hamiltonian) quantum systems is that their poles lie on the imaginary axis and that neither a coherent controller nor physically relevant structured uncertainties can alter this situation. This changes for open systems where d...
Preprint
Full-text available
We explore the use of policy gradient methods in reinforcement learning for quantum control via energy landscape shaping of XX-Heisenberg spin chains in a model agnostic fashion. Their performance is compared to finding controllers using gradient-based L-BFGS optimisation with restarts, with full access to an analytical model. Hamiltonian noise and...
Preprint
Full-text available
Many tools exist for the quantification of GABA-edited magnetic resonance spectroscopy (MRS) data. Despite a recent consensus effort by the MRS community, literature comparing them is sparse but indicates a methodological bias. While in-vivo data sets can ascertain the level of agreement between tools, ground-truth is required to establish accuracy...
Preprint
The robustness of quantum control in the presence of uncertainties is important for practical applications but their quantum nature poses many challenges for traditional robust control. In addition to uncertainties in the system and control Hamiltonians and initial state preparation, there is uncertainty about interactions with the environment lead...
Preprint
Full-text available
Quantification of metabolites from magnetic resonance spectra (MRS) has many applications in medicine and psychology, but remains a challenging task despite considerable research efforts. For example, the neurotransmitter $\gamma$-aminobutyric acid (GABA), present in very low concentration in vivo, regulates inhibitory neurotransmission in the brai...
Preprint
Full-text available
Purpose: Many tools exist for quantifying magnetic resonance spectroscopy (MRS) data. Literature comparing them is sparse but indicates potential methodological bias. We benchmark MRS analysis tools to elucidate this. Methods: Four series of phantom experiments, including both solutions and tissue-mimicking gels, with constant concentrations of NAA...
Preprint
Full-text available
Quantum spin networks form a generic system to describe a range of quantum devices for quantum information processing and sensing applications. Understanding how to control them is essential to achieve devices with practical functionalities. Energy landscape shaping is a novel control paradigm to achieve selective transfer of excitations in a spin...
Article
The cover image, by E. Jonckheere et al., is based on the Research Article Jonckheere-Terpstra test for nonclassical error versus log-sensitivity relationship of quantum spin network controllers, DOI: 10.1002/rnc.4022.
Article
Full-text available
Selective transfer of information between spin-1/2 particles arranged in a ring is achieved by optimizing the transfer fidelity over a readout time window via shaping, externally applied, static bias fields. Such static control fields have properties that clash with the expectations of classical control theory. Previous work has shown that there ar...
Article
Full-text available
Control laws for selective transfer of information encoded in excitations of a quantum network, based on shaping the energy landscape using time-invariant, spatially-varying bias fields, can be successfully designed using numerical optimization. Such control laws, already departing from classicality by replacing closed-loop asymptotic stability wit...
Article
Full-text available
Selective information transfer in spin ring networks by landscape shaping control has the property that the error $1-\mathrm{prob}$, where $\mathrm{prob}$ is the transfer success probability, and the sensitivity of the probability to spin coupling errors are "positively correlated," meaning that both are statistically increasing across a family of...
Article
Full-text available
By augmenting an in-house developed, experimentally verified Monte Carlo device simulator with a Bloch equation model with a spin-orbit interaction Hamiltonian accounting for Dresselhaus and Rashba couplings, we simulate electron spin transport in a \SI{25}{nm} gate length InGaAs MOSFET. We observe non-uniform decay of the net magnetization between...
Article
Full-text available
Information encoded in networks of stationary, interacting spin-1/2 particles is central for many applications ranging from quantum spintronics to quantum information processing. Without control, however, information transfer through such networks is generally inefficient. High-fidelity efficient transfer of excitations is achieved solely by shapin...
Article
Full-text available
Simplifying the geometry of a CAD model using defeaturing techniques enables more efficient discretisation and subsequent simulation for engineering analysis problems. Understanding the effect this simplification has on the solution helps to decide whether the simplification is suitable for a specific simulation problem. It can also help to underst...
Article
Full-text available
Spin networks are endowed with an information transfer fidelity (ITF), which defines an absolute upper bound on the probability of transmission of an excitation from one spin to another. The ITF is easily computable, but the bound can be reached asymptotically in time only under certain conditions. General conditions for attainability of the bound...
Conference Paper
Full-text available
Propagation of information encoded in spin degrees of freedom through networks of coupled spins enables important applications in spintronics and quantum information processing. We study control of information propagation in networks of spin-$\tfrac{1}{2}$ particles with uniform nearest neighbour couplings forming a ring with a single excitation in...
Article
Full-text available
Automatic feature recognition aids downstream processes such as engineering analysis and manufacturing planning. Not all features can be defined in advance; a declarative approach allows engineers to specify new features without having to design algorithms to find them. Naive translation of declarations leads to executable algorithms with high time...
Article
Full-text available
In engineering analysis, CAD models are often simplified by removing features, enabling meshing to be quicker and more reliable; the resulting smaller meshes in turn lead to faster analysis. Finding features by hand is tedious, and there is a need to automate this process. A declarative approach to feature recognition allows engineers to define fea...
Article
Full-text available
We compare the accuracy, precision and reliability of different methods for estimating key system parameters for two-level systems subject to Hamiltonian evolution and decoherence. It is demonstrated that the use of Bayesian modelling and maximum likelihood estimation is superior to common techniques based on Fourier analysis. Even for simple two-p...
Article
Full-text available
Networks of spins, or spintronic networks, are given an Information Transfer Fidelity (ITF) derived from an upper bound on the probability of transmission of the excitation from one spin to another. It is shown that this theoretical bound can be reached asymptotically in time under certain conditions. The process of achieving maximum transfer proba...
Article
Full-text available
Information flow in quantum spin networks is considered. Two types of control -- temporal bang-bang switching control and control by varying spatial degrees of freedom -- are explored and shown to be effective in speeding up information transfer and increasing transfer fidelities. The control is model-based and therefore relies on accurate knowledg...
Article
Full-text available
The purpose of this paper is to exhibit a quantum network phenomenon - the anti-core---that goes against the classical network concept of congestion core. Classical networks idealized as infinite, Gromov hyperbolic spaces with least-cost path routing (and subject to a technical condition on the Gromov boundary) have a congestion core, defined as a...
Article
Full-text available
Three-dimensional surface registration transforms multiple three-dimensional data sets into the same coordinate system so as to align overlapping components of these sets. Recent surveys have covered different aspects of either rigid or nonrigid registration, but seldom discuss them as a whole. Our study serves two purposes: 1) To give a comprehens...
Article
Bas-reliefs are a form of flattened artwork, part-way between 3D sculpture and 2D painting. Recent research has considered automatic bas-relief generation from 3D scenes. However, little work has addressed the generation of bas-reliefs from 2D images. In this paper, we propose a method to automatically generate bas-relief surfaces from frontal phot...
Article
Centroidal Voronoi tessellations and optimal Delaunay triangulations can be approximated efficiently by non-linear optimisation algorithms. This paper demonstrates that the point distribution used to initialise the optimisation algorithms is important. Compared to conventional random initialisation, certain low-discrepancy point distributions help...
Conference Paper
Full-text available
We present the results of our submission to the MediaEval 2012 Placing Task. We used a framework that combines language models and similarity search, which improves our system from last year by using a different feature selection technique, extending our similarity search, tapping into new types of information for videos without any tags and includ...
Conference Paper
Full-text available
We develop a geometric approach to spin networks with Heisenberg or XX coupling. Geometry is acquired by defining a distance on the discrete set of spins. The key feature of the geometry of such networks is their Gauss curvature κ, viewed here as the ability to isometrically embed the chain in the standard Riemannian manifold of curvature κ. Here w...
Article
Full-text available
We develop a geometric approach to spin networks with Heisenberg or XX coupling. Geometry is acquired by defining a distance on the discrete set of spins. The key feature of the geometry of such networks is their Gauss curvature $\kappa$, viewed here as the ability to isometrically embed the chain in the standard Riemannian manifold of curvature $\...
Article
Full-text available
Current reverse engineering systems are able to generate simple valid boundary representation (B-rep) models from 3D range data. Such models suffer from various inaccuracies caused by noise in the input data and algorithms. Reverse engineered geometric models may be beautified by finding approximate geometric regularities in such a model, and impos...
Article
Full-text available
A measure for the maximum quantum information transfer capacity (ITC) between nodes of a spin network is defined, and shown to induce a metric on a space of equivalence classes of nodes for homogeneous chains with XX and Heisenberg couplings. The geometry and curvature of spin chains with respect of this metric are studied and compared to the physi...
Conference Paper
Full-text available
In region machining, neighbouring regions may be close together, but disconnected. Boundary curves may also have unwanted geometric artifacts caused by approximation and discretisation. We present a strategy to improve the topology and geometry of such boundary curves, allowing the generation of better tool paths, and in turn, improved tool wear an...
Conference Paper
Full-text available
Identifying the Hamiltonian of a quantum system from experimental data is considered. General limits on the identifiability of model parameters with limited experimental resources are investigated, and a specific Bayesian estimation procedure is proposed and evaluated for a model system where a-priori information about the Hamiltonian's structure i...
Article
Finding design intent embodied as high-level geometric relations between a CAD model’s sub-parts facilitates various tasks such as model editing and analysis. This is especially important for boundary-representation models arising from, e.g., reverse engineering or CAD data transfer. These lack explicit information about design intent, and often th...
Article
Full-text available
An algorithm is presented to automatically generate bas-reliefs based on adaptive histogram equalization (AHE), starting from an input height field. A mesh model may alternatively be provided, in which case a height field is first created via orthogonal or perspective projection. The height field is regularly gridded and treated as an image, enabli...
Article
Full-text available
We consider the problem of computing a parting line for a mold for a complex mesh model, given a parting direction, and the related problem of removing small undercuts, either preexisting, or resulting from the parting line. Existing parting line algorithms are unsuitable for use with complex meshes: the faceted nature of such models leads to a par...
Article
This paper analyses the noise present in range data measured by a Konica Minolta Vivid 910 scanner, in order to better characterise real scanner noise. Methods for denoising 3D mesh data have often assumed the noise to be Gaussian, and independently distributed at each mesh point. We show via measurements of an accurately machined almost planar tes...
Article
An approach to mesh denoising based on the concept of random walks is examined. The proposed method consists of two stages: face normal filtering, followed by vertex position updating to integrate the denoised face normals in a least-squares manner. Face normal filtering is performed by weighted averaging of normals in a neighbourhood. A novel appr...
Conference Paper
Full-text available
This paper discusses noise in range data measured by a Konica Minolta Vivid 910 scanner. Previous papers considering denoising 3D mesh data have often used artificial data comprising Gaussian noise, which is independently distributed at each mesh point. Measurements of an accurately machined, almost planar test surface indicate that real scanner da...
Conference Paper
Full-text available
In [2] we presented an algorithm for decomposing a boundary representation model hierarchically into regularity features by recovering broken symmetries. The algorithm adds new recoverable edges and faces, which can be constructed from existing geometry. This generates positive and negative volumes giving simple, more symmetric sub-parts of the mod...
Working Paper
Various industrial applications require point sets that cover arbitrarily shaped surfaces of 3D objects. The nature of the sampling required depends on the application; while common machining or inspection processes need regularly arranged points for smooth path generation, the application described in this paper requires a more subtle distribution...
Article
Detecting approximate symmetries of parts of a model is important when attempting to determine the geometrical design intent of approximate boundary-representation (B-rep) solid models produced e.g. by reverse engineering systems. For example, such detected symmetries may be enforced exactly on the model to improve its shape, to simplify its analys...
Article
Full-text available
We present a simple and fast mesh denoising method, which can remove noise effectively while preserving mesh features such as sharp edges and corners. The method consists of two stages. First, noisy face normals are filtered iteratively by weighted averaging of neighboring face normals. Second, vertex positions are iteratively updated to agree with...
Article
Full-text available
Reverse engineering of reliefs aims to turn an existing relief superimposed on an underlying surface into a geometric model which may be applied to a different base surface. Steps in this process include segmenting the relief from the background, and describing it as an offset height field relative to the underlying surface. We have previously cons...
Conference Paper
Full-text available
A novel point sampling framework for polygonal meshes is presented, based on sampling a mesh according to a density-controlled low-discrepancy distribution. The local sampling density can be controlled by a density functional defined by the user, e.g. to preserve local features, or to achieve desired data reduction rates. To sample the mesh, it is...
Conference Paper
Full-text available
Decorative reliefs are widely used for e.g. packaging and porcelain design. In periodic reliefs, the relief repeats a pattern, for example all the way around an underlying surface of revolution. Reverse-engineering of existing reliefs allows them to be re-applied to different base surfaces; we show here how to segment a single repeat unit of a peri...
Article
Full-text available
Segmentation of geometric reliefs from a textured background has various applications in reverse engineering. We consider two approaches to solve this problem. The first classifies parts of a surface mesh as relief or background, and then uses a snake which moves inwards towards the desired relief boundary, which is coarsely located using an energy...
Conference Paper
Full-text available
Motivated by the need to detect design intent in approximate boundary representation models, we give an algorithm to detect incomplete symmetries of discrete points, giving the models' potential local symmetries at various automatically detected tolerances. Here, incomplete symmetry is defined as a set of incomplete cycles which are constructed by,...
Conference Paper
Full-text available
This paper considers an approach to mesh denoising based on the concept of random walks. The proposed method consists of two stages: a face normal filtering procedure, followed by a vertex position updating procedure which integrates the denoised face normals in a least-squares sense. Face normal filtering is performed by weighted averaging of norm...
Conference Paper
Full-text available
This paper considers the mold design problem of computing a parting line for a complex mesh model, given a parting direction. Existing parting line algorithms are unsuitable for this case, as local variations in the orientations of the facets of such models lead to a parting line which zig-zags across the surface in an undesirable way. This paper p...