Tehnike zrcaljenja u Real-Time računalnoj grafici

Reflections have a long history in computer graphics, as they are important for conveying a sense of realism as well as depth and proportion. Their implementations come with a multitude of difficulties, and each solution typically has various trade-offs. Approaches highly depend on the geometry of the reflective surface since curved reflectors are usually more difficult to portray accurately. Techniques can typically be categorized by whether they work with the actual geometry of the reflected objects or with an image of these objects. For curved surfaces, image-based techniques are usually preferred, whereas for planar surfaces the reflected geometry can be used more easily because of the lack of distortion. With current advances in graphics hardware technology, ray tracing is also becoming more viable for real-time applications. Many modern solutions often combine multiple approaches to form a hybrid technique. In this paper, we give an overview of the techniques used in computer graphics applications to create real-time reflections. We highlight the trade-offs that have to be dealt with when choosing a particular technique, as well as their ability to produce interreflections. Finally, we describe how contemporary state-of-the-art rendering engines deal with reflections.Zrcaljenja imaju dugu povijest primjene u računalnoj grafici zbog njihove važnosti u prenošenju realističnosti prikaza te prikaza dubine i omjera na slikama. Pri implementaciji zrcaljenja dolazimo do raznih teškoća i svako novo rješenje često imaju svoju cijenu. Pristupi implementacije ovise o geometriji plohe na kojoj leži prikaz, Što je ploha zakrivljenija, to je teže postići vjerni prikaz. Tehnike možemo kategorizirati u one koje rade sa stvarnom geometrijom zrcaljenih objekata te one koje rade samo sa slikama objekata. Kod zakrivljenih ploha koriste se tehnike bazirane na slikama, dok se kod ravninskih ploha koristi zrcaljena geometrija jer nema iskrivljenja. Zahvaljujući trenutnom razvoju tehnologije grafičkih hardvera, metoda praćenja zraka (ray tracing) postaje sve isplativija u real-time primjeni. Mnoga moderna rješenja kombiniraju razne pristupe i dolazi do hibridnih tehnika. U ovom radu dajemo pregled tehnika korištenih u primjeni računalne grafike za postizanje real-time zrcalnih slika. Naglašavamo probleme koji nastaju pri korištenju određene tehnike te njihove mogućnosti u pogledu stvaranja međuzrcaljenja. Naposljetku, opisujemo kako moderni alati za renderiranje rješavaju probleme zrcaljenj

Riemannian tangent space mapping and elastic net regularization for cost-effective EEG markers of brain atrophy in Alzheimer's disease

The diagnosis of Alzheimer's disease (AD) in routine clinical practice is most commonly based on subjective clinical interpretations. Quantitative electroencephalography (QEEG) measures have been shown to reflect neurodegenerative processes in AD and might qualify as affordable and thereby widely available markers to facilitate the objectivization of AD assessment. Here, we present a novel framework combining Riemannian tangent space mapping and elastic net regression for the development of brain atrophy markers. While most AD QEEG studies are based on small sample sizes and psychological test scores as outcome measures, here we train and test our models using data of one of the largest prospective EEG AD trials ever conducted, including MRI biomarkers of brain atrophy.Comment: Presented at NIPS 2017 Workshop on Machine Learning for Healt

Location recommendations from user mobile trajectories

Location Recommenders (LR) are location based recommender systems which use locations from historic user trajectories to recommend new places such as locations of sights, museums, or other places of interest by learning past preferences. In this work we analyze the viability of different LR models to be used with mobile hotspots which are handed out to tourists in different hotels in the city of Vienna. As these devices can be potentially used by thousands of users at any given time, we explore different methods of data collection, management and visualization. Whenever systems are used in assisting humans with their decision processes, the implications of algorithmically made recommendations need to be analyzed. For LR fairness can be defined for both users and locations, as both can be subject to unfairness. We propose a framework in which multiple fairness aspects can be formulated. We compare the LR in three fairness aspects formulated in the framework and their predictive accuracy, to give a final assessment of which LR is preferable in this scenario.7

O strukturalnim svojstvima Voronoi dijagrama

A Voronoi diagram is a tessellation technique, which subdivides space into regions in proximity to a given set of objects called seeds. Patterns emerging naturally in biological processes (for example, in cell tissue) can be modelled in a biomimicry process via Voronoi diagrams. As they originate in nature, we investigate the physical properties of such patterns to determine whether they are optimal given the constraints imposed by surrounding geometry and natural forces. This paper describes under what circumstances the Voronoi tessellation has optimal (structural) properties by surveying recent studies that apply this tessellation technique across different scales. To investigate the properties of random and optimized Voronoi tessellations in comparison to a regular tessellation method, we additionally run and evaluate a simulation in Karamba3D, a parametric structural engineering tool for Rhinoceros3D. The novelty of this research lies in presenting a simple and straightforward simulation of Voronoi diagrams and highlighting how and where their advantages over regular tessellations can be exploited by surveying more advanced approaches as found in literature.Voronoi dijagram je tehnika popločavanja koja čini particiju prostora s obzirom na udaljenosti od zadanog skupa objekata koje nazivamo lokacije (en. seeds). Uzorke koji nastaju tokom bioloških procesa (na primjer u staničnom tkivu) možemo modelirati biomimikrijskim procesima korištenjem Voronoi dijagrama. Kako je izvor takvih struktura prirodan, proučavamo fizička svojstva takvih uzoraka da bismo ispitali njihovu optimalnost s obzirom na ograničenja koja nameću vanjska geometrija i prirodne sile. U ovom članku opisujemo slučajeve u kojima je Voronoi popločavanje (strukturalno) optimalno proučavanjem nedavnih ispitivanja koja ovo popločavanje koriste u različitim razmjerima. Da bismo usporedili svojstva slučajnog te optimiziranog Voronoi popločavanja i metode pravilnog popločavanja, razvili smo simulaciju korištenjem Karamba3D, alata za parametarsko strukturalno inženjersko modeliranje unutar programam Rhinoceros3D. Novost ovog istraživanja je predstavljanje jednostavne i izravne simulacije Voronoi dijagrama, isticanje njenih prednosti nad pravilnim popločavanjima te pregled korištenja tih prednosti u naprednijim pristupima iz literature

Cumulation, crash, coherency: a cryptocurrency bubble wavelet analysis

After its price peaked in 2017, Bitcoin lost almost half of its value in US Dollars within one month, which in turn is likely to have influenced the behaviour of market participants – many of who were lay investors. We hypothesize that after the peak, there was a structural change in the relationships between cryptocurrencies towards instability, as indicated by increased interdependence. We utilize wavelet coherence analysis of intraday data (5-minute resolution) to investigate the dynamics between a variety of cryptocurrencies in time-frequency space. Accompanied by visualizations depicting bubble dynamics, our robust and highly-significant quantitative results confirm our hypothesis