MixAR: A Multi-Tracking Mixed Reality System to Visualize Virtual Ancient Buildings Aligned Upon Ruins

MixAR: A Multi-Tracking Mixed Reality System to Visualize Virtual Ancient Buildings Aligned Upon Ruins

Telmo Adão, Luís Pádua, David Narciso, Joaquim João Sousa, Luís Agrellos, Emanuel Peres, Luís Magalhães
Copyright: © 2019 |Pages: 33
DOI: 10.4018/JITR.2019100101
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MixAR, a full-stack system capable of providing visualization of virtual reconstructions seamlessly integrated in the real scene (e.g. upon ruins), with the possibility of being freely explored by visitors, in situ, is presented in this article. In addition to its ability to operate with several tracking approaches to be able to deal with a wide variety of environmental conditions, MixAR system also implements an extended environment feature that provides visitors with an insight on surrounding points-of-interest for visitation during mixed reality experiences (positional rough tracking). A procedural modelling tool mainstreams augmentation models production. Tests carried out with participants to ascertain comfort, satisfaction and presence/immersion based on an in-field MR experience and respective results are also presented. Ease to adapt to the experience, desire to see the system in museums and a raised curiosity and motivation contributed as positive points for evaluation. In what regards to sickness and comfort, the lowest number of complaints seems to be satisfactory. Models' illumination/re-lightning must be addressed in the future to improve the user's engagement with the experiences provided by the MixAR system.
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1. Introduction

The Virtualization Continuum (VC) proposed by Milgram and Kishino (1994) consists of a representational scale concept that extends from a Virtual Environment at one end to a Real Environment at the other. In-between lies Mixed Reality (MR) that represents every environment resulting from a combination of the virtual and the real environments - with varying levels of mixture between the two - where virtual and real objects/persons may interact. In the VC, an Augmented Reality (AR) approach is placed closer to the real environment’s extreme, since the real prevails over the virtual: a user visualizes the real environment with some added virtual objects. AR approaches usually have a process underlying the augmentation of virtual models upon real-environments known as tracking (Azuma, 1997), that accordingly to Narciso et al. (2015), can be divided into three main types: sensor-based, vision-based and hybrid. While the former uses tracking devices (location and inertial), vision-based tracking is characterized by a precise registration of a capturing device (e.g. camera) upon a real point-of-interest (POI). Furthermore, it can be marker-based (e.g. using fiducial tags) or markerless (relying uniquely on structural features of the real-environment). Hybrid tracking explores synergies between different tracking techniques to overcome their individual disadvantages. Selection of a proper tracking technique should be made considering conditions such as light, terrain morphology and anti-handling policies commonly found in protected spaces, such as cultural heritage sites. Regarding an Augmented Virtuality (AV) approach, it is placed closer to the virtual environment’s extreme in the VC, since the virtual prevails over the real: a user visualizes a virtual environment to where some parts of the real environment were “transferred”.

The VC has been explored by an increasing number of approaches being used in archaeology and in other areas related with cultural heritage. The aim is to provide accurate representations of ancient structures, especially those no longer available for observation at their full splendour due to severe or complete deterioration. Typically, Virtual Reality (VR) applications towards this focus confine the users’ experience to an indoor space equipped with the necessary technology to deliver fully virtualized contents. Another possibility is to use AR to leverage virtual representations, providing indoor and outdoor experiences capable of seamlessly merging reality and virtual data in a single compelling environment, as it was demonstrated in areas such as archaeology and cultural heritage (Fritz, Susperregui, & Linaza, 2005; Stricker, Dähne, Seibert, & al, 2001). This can be particularly interesting to: (1) promote the general public participation in areas such as culture, history or archaeology, considering the digital heritage's importance in modern society and (2) provide tools to support professionals - such as historians and archaeologists - in tasks related with the study and analysis of damaged or completely destroyed ancient structures.

MixAR - an adaptive MR system - is a research and development project (reference FEDER/03880/2014, Portugal) developed in the University of Trás-os-Montes e Alto Douro (UTAD, Vila Real, Portugal) in partnership with GEMA Digital and Technology Agency enterprise (Porto, Portugal), whose main goal is to have a manageable harmony between the amount of reality and virtuality displayed in cultural heritage visitations. It is a solution capable of providing in situ visualization of reliable virtual reconstructions seamlessly superimposed to ruins present in the real scene that can be freely explored by the visitor. To achieve it, a methodology that balances the blend level between real and virtual scenes while the user is moving freely in an archaeological site was developed. Thus, when the visitor is outside a virtual building (outdoor scene) an AR approach (in which the real world prevails) is used; if the visitor moves into a virtual building’s interior, virtuality takes over the experience, placing the visitor inside a fully synthesized environment. Transition occurs smoothly to provide a sensation of naturalness, as it was specified by Magalhães et al. (2014).

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