Marcos A. Rodrigues

Optical techniques for 3D surface reconstruction in computer-assisted laparoscopic surgery

One of the main challenges for computer-assisted surgery (CAS) is to determine the intra-operative morphology and motion of soft-tissues. This information is prerequisite to the registration of multi-modal patient-specific data for enhancing the surgeons navigation capabilities by observing beyond exposed tissue surfaces and for providing intelligent control of robotic-assisted instruments. In minimally invasive surgery (MIS), optical techniques are an increasingly attractive approach for in vivo 3D reconstruction of the soft-tissue surface geometry. This paper reviews the state-of-the-art methods for optical intra-operative 3D reconstruction in laparoscopic surgery and discusses the technical challenges and future perspectives towards clinical translation. With the recent paradigm shift of surgical practice towards MIS and new developments in 3D optical imaging, this is a timely discussion about technologies that could facilitate complex CAS procedures in dynamic and deformable anatomical regions.

Special issue on registration and fusion of range images

This special issue contains nine high quality papers representative of the state-of-the art technologies used to acquire and process range image data. Following the call for papers, 23 manuscripts were received which were reviewed by a pool of 37 expert referees. We are thankful to these anonymous referees for their invaluable work which, as ever, is essential to maintain the high standards of CVIU. All selected papers carry an element of novelty, and we hope that this issue will be useful to theoreticians and practitioners alike.

Indexing uncoded stripe patterns in structured light systems by maximum spanning trees

Structured light is a well-known technique for capturing 3D surface measurements but has yet to achieve satisfactory results for applications demanding high resolution models at frame rate. For these requirements a dense set of uniform uncoded white stripes seems attractive. But the problem of relating projected and recorded stripes, here called the Indexing Problem, has proved to be difficult to overcome reliably for uncoded patterns. We propose a new algorithm that uses the maximum spanning tree of a graph defining potential connectivity and adjacency in recorded stripes. Results are significantly more accurate and reliable than previous attempts. We do however also identify an important limitation of uncoded patterns and claim that, in general, additional stripe coding is necessary. Our algorithm adapts easily to accommodate a minimal coding scheme that increases neither sample size nor acquisition time.

On the representation of rigid body transformations for accurate registration of free-form shapes

Abstract In this paper we consider representation issues of rigid body transformations based on geometric properties of reflected correspondence vectors. A sufficient and necessary representation of rigid body transformations is put forward followed by an accurate and robust algorithm for the registration of free-form surfaces. The algorithm makes full use of global rigid motion constraints derived from the representation of rigid body transformations and can effectively deal with occlusion, noise, and appearance and disappearance of points. A comparative study based on both synthetic data and real images show that the registration method is accurate and robust.

Developing rigid motion constraints for the registration of free-form shapes

We propose a novel method to deal with sphere ambiguity, occlusion, appearance and disappearance of points in image registration. We have developed a number of rigid motion constraints through analysis of geometrical properties of reflected correspondence vectors synthesised into a single coordinate frame. The properties are used as further constraints to eliminate false matches obtained by the iterative closest point criterion. A number of experiments based on both synthetic data and real images demonstrate that the proposed method is accurate, robust, and efficient for the registration of free-form shapes.

Geometrical Analysis of Two Sets of 3D Correspondence Data Patterns for the Registration of Free-Form Shapes

The iterative closest point (ICP) algorithm represents an efficient method to establish an initial set of possible correspondences between two overlapping range images. An inherent limitation of the algorithm is the introduction of false matches, a problem that has been tackled by a variety of schemes mainly based on local invariants described in a single coordinate frame. In this paper we propose using global rigid motion constraints to deal with false matches. Such constraints are derived from geometric properties of correspondence vectors bridging the points described in different coordinate frames before and after a rigid motion. In order to accurately and efficiently estimate the parameters of interest, the Monte Carlo resampling technique is used and motion parameter candidates are then synthesised by a median filter. The proposed algorithm is validated based on both synthetic data and real range images. Experimental results show that the proposed algorithm has advantages over existing registration methods concerning robustness, accuracy, and efficiency.

Learning and diagnosis in manufacturing processes through an executable Bayesian network

In this paper we present a novel approach to modelling a manufacturing process that allows one to learn about causal mechanisms of manufacturing defects through a Process Modelling and Executable Bayesian Network (PMEBN). The method combines probabilistic reasoning with time dependent parameters which are of crucial interest to quality control in manufacturing environments. We demonstrate the concept through a case study of a caravan manufacturing line using inspection data.

Statistical image analysis for pose estimation without point correspondences

Abstract We propose a novel algorithm for correspondenceless pose estimation based on a realistic camera setup for a class of industrial problems. The algorithm provides unique closed form solutions to all parameters of interest and its superior performance is demonstrated by extensive comparisons with an epipolar geometry-based algorithm.

An intelligent real time 3D vision system for robotic welding tasks

MARWIN is a top-level robot control system that has been designed for automatic robot welding tasks. It extracts welding parameters and calculates robot trajectories directly from CAD models which are then verified by real-time 3D scanning and registration. MARWINs 3D computer vision provides a user-centred robot environment in which a task is specified by the user by simply confirming and/or adjusting suggested parameters and welding sequences. The focus of this paper is on describing a mathematical formulation for fast 3D reconstruction using structured light together with the mechanical design and testing of the 3D vision system and show how such technologies can be exploited in robot welding tasks.

Empirically derived design issues in auditory information processing for mobile telephony

This paper investigates empirically design issues in auditory information processing, relevant to interfaces for mobile telephony. This investigation forms the initial part of a larger experimental programme, which aims to investigate design methodologies for auditory-multimedia interfaces. Structured musical and environmental audio was used to communicate simple and complex (i.e., larger amounts) information for mobile telephony. The contribution of this paper is in the empirical investigation of the perceptual principles involved in using auditory stimuli to communicate information rather than the mere application of sound in this problem domain. Some of these experiments also aim to communicate information that would normally be communicated using the visual displays of mobile devices. Results indicate perceptual issues that need to be considered in the design process of auditory interfaces. Memory demands on users may in some cases prevent the correct interpretation of the auditory stimuli. Other issues observed to help the designing process of auditory user interfaces include the creation of perceptual context, semantic coding and auditory user interaction model.