Borut Zalik

Sweep-line algorithm for constrained Delaunay triangulation

This paper introduces a new algorithm for constrained Delaunay triangulation, which is built upon sets of points and constraining edges. It has various applications in geographical information system (GIS), for example, iso‐lines triangulation or the triangulation of polygons in land cadastre. The presented algorithm uses a sweep‐line paradigm combined with Lawsons legalisation. An advancing front moves by following the sweep‐line. It separates the triangulated and non‐triangulated regions of interest. Our algorithm simultaneously triangulates points and constraining edges and thus avoids consuming location of those triangles containing constraining edges, as used by other approaches. The implementation of the algorithm is also considerably simplified by introducing two additional artificial points. Experiments show that the presented algorithm is among the fastest constrained Delaunay triangulation algorithms available at the moment.

Efficient method for lossless LIDAR data compression

Light Detection and Ranging (LIDAR) has become one of the prime technologies for rapid collection of vast spatial data, usually stored in a LAS file format (LIDAR data exchange format standard). In this article, a new method for lossless LIDAR LAS file compression is presented. The method applies three consequent steps: a predictive coding, a variable-length coding and an arithmetic coding. The key to the method is the prediction schema, where four different predictors are used: three predictors for x, y and z coordinates and a predictor for scalar values, associated with each LIDAR point. The method has been compared with the popular general-purpose methods and with a method developed specially for compressing LAS files. The proposed method turns out to be the most efficient in all test cases. On average, the LAS file is losslessly compressed to 12% of its original size.

An Efficient Code‐Based Voxel‐Traversing Algorithm

The paper considers an efficient approach to traversing a uniformly‐subdivided space pierced by a line segment. A voxel, as the basic constituent element of the uniformly subdivided space, is restricted to having the form of a cube. The algorithm works in two steps. In the first step, the so‐called Bresenham voxels are identified and, by comparing their position codes, their type of connectivity is determined. To achieve the required connectivity between neighbouring voxels, the second step of the algorithm is applied to find the missing voxels. In this way, the algorithm efficiently switches between face‐, edge‐ and vertex‐connectivity. Although the algorithm works with oating‐point precision, it is extremely computationally efficient, and tests of speed compared with the Müller, Cleary & Wyvill, Amanatides & Woo, and Zemčik algorithms are described.

Towards a low-cost mobile subcutaneous vein detection solution using near-infrared spectroscopy.

Excessive venipunctures are both time- and resource-consuming events, which cause anxiety, pain, and distress in patients, or can lead to severe harmful injuries. We propose a low-cost mobile health solution for subcutaneous vein detection using near-infrared spectroscopy, along with an assessment of the current state of the art in this field. The first objective of this study was to get a deeper overview of the research topic, through the initial team discussions and a detailed literature review (using both academic and grey literature). The second objective, that is, identifying the commercial systems employing near-infrared spectroscopy, was conducted using the PubMed database. The goal of the third objective was to identify and evaluate (using the IEEE Xplore database) the research efforts in the field of low-cost near-infrared imaging in general, as a basis for the conceptual model of the upcoming prototype. Although the reviewed commercial devices have demonstrated usefulness and value for peripheral veins visualization, other evaluated clinical outcomes are less conclusive. Previous studies regarding low-cost near-infrared systems demonstrated the general feasibility of developing cost-effective vein detection systems; however, their limitations are restricting their applicability to clinical practice. Finally, based on the current findings, we outline the future research direction.

Comparison of viewshed algorithms on regular spaced points

Viewshed is a basic visibility structure and represents all visible points from a given viewpoint. The paper gives a survey of non-parallel viewshed algorithms using regular spaced points. At first, a comprehensive background of the problem is given, then the existing methods (R3, R2, XDraw, method based on the line rasterisation) are introduced briefly. They have been implemented in 11 variants. Real terrain data and fractal generated terrains have been used for their comparison against spent CPU time and the accuracy of a computed visibility information.

An Integer One‐Pass Algorithm for Voxel Traversal

Voxel traversing along a line in a uniformly divided voxel space is frequently needed in different applications of computer graphics. The paper presents a new integer one‐pass algorithm for this problem. In 2D, the proposed approach is based on a modification of the well‐known Bresenham algorithm. The algorithm is then extended in 3D where a special case may occur. It is characterized by a simple discriminator. A derivation for this discriminator given in the paper confirms that all calculations can be realized using only integer arithmetic. In this way, the accumulation of rounding errors is completely eliminated, and a robust and compact implementation can be easily achieved. One of the main advantages of the proposed algorithm is that it visits 1–3 voxels during each iteration thus assuring its efficiency. The algorithm has been compared with other algorithms for voxel traversing by measuring spent CPU time. For comparison, Cleary & Wyvills, Amanatides & Woos, and Code‐based algorithm have been used. The proposed algorithm is faster than the referenced algorithms.

An innovative approach to near-infrared spectroscopy using a standard mobile device and its clinical application in the real-time visualization of peripheral veins

BackgroundExcessive venipunctures are a significant problem both in emergency rooms and during hospital stays. Near-infrared (NIR) illumination devices improve venipuncture success rate but their usage is limited by their availability and economic cost. The objectives of this study were to develop a low-cost NIR spectroscopy prototype from a standard mobile device, to evaluate its efficacy and acceptance as an educational tool, and in a clinical setting.MethodsThrough a user-centric design process a prototype device was developed. Its educational efficacy was evaluated through a non-invasive, observational study (20 student clinicians, 25 subjects) and its acceptance was assessed using quantitative and qualitative analysis. A smaller clinical trial was performed by a group of 4 medical professionals over a period of 6 weeks that involved 64 patients.ResultsThe prototype enables real-time visualization of peripheral veins on a variety of Android-based devices. The prototype was 35.2% more successful in visualizing and locating veins (n = 500 attempts) than the nursing students. The acceptance assessment revealed high perception of usefulness, satisfaction, and ease of use. In the clinical trial, 1.6 (SD 1.3) additional veins per patient were identified compared with the traditional visualization methods.ConclusionsTo the best of our knowledge this is the first study that describes the design, feasibility and application of an NIR spectroscopy prototype developed on a standard mobile device.

Surface reconstruction algorithms in cultural heritage digital representation

The goal of our work is to present the application of the modern technologies and computer graphics algorithms in the field of cultural heritage reconstruction and its protection. Here we describe a methodology for digital 3D acquisition of the ldquoStecakrdquo (Stecak - plural Stecci - specific Bosnian Middle Ages tombstones), with purpose of its study and presentation. 3D laser scanning technology has been selected as the most accurate technology available for replicating a complete sampling of the very complex Stecacuteaks surface. Afterwards, three algorithms for surface reconstruction were used to reconstruct its surface from point cloud data. This paper presents the results of that reconstruction and overview of various applications of reconstructed models.

Representing Geometric Objects Using Constraint Description Graphs

The paper demonstrates how geometrical constraints can be applied to add a new level of abstraction to description of geometrical objects. Special attention is given to the interactive insertion of constraints. To support incremental design each inserted constraint has to be solved as soon as possible. Because of this requirement a local propagation of known states is used for constraint solving. It is supported by a biconnected constraint description graph structure. The benefits of this structure are insensibility to the order of inserted constraints and ability of replacing constraints with their inverse couples. To override the ambiguities at constraint solving the approximal values of geometrical elements which are inserted through a sketch are used. From the biconnected constraint description graph an acyclic constraint description graph is generated easily. It is suitable for the generation of instances of generic objects.

GPU-Based Online Optimization of Low Voltage Distribution Network Operation

This paper proposes a parallelized online optimization of low voltage distribution network (LVDN) operation. It is performed on a graphics processing unit (GPU) by combining the optimization procedure with the load flow method. In the case study, performed for the test LVDN with distributed generators (DGs) and controllable loads, differential evolution optimization based on a backward–forward sweep load flow method was parallelized on GPU. The goal of online optimization is to keep the LVDN voltage profile within the prescribed limits, to minimize LVDN losses, and to enable demand response functionality. This is achieved by the optimization determined reference values for the controllable load’s operation, and the reactive power generation, and active power curtailment of DGs. The results show that the parallelized GPU implemented optimization can be significantly faster than similar implementation on a central processing unit, and is, therefore, suitable for the online optimization of the presented LVDN.