Inside Out – Outside In Exploring Indoor–Outdoor Indirect Augmented Reality Positioning in Cultural Heritage Gunnar Liestøl 1(B) , Šar¯ unas Ledas 2 , Žilvinas Ledas 2,3 , José Cruz 4 , Tomás Carla 4 , and Vanessa Antunes 4 1 Department of Media & Communication, University of Oslo, Oslo, Norway gunnar.liestol@media.uio.no 2 Tag Og Joy, Vilnius, Lithuania sarunas.ledas@tagofjoy.lt 3 Institute of Computer Science, Vionius University, Vilnius, Lithuania 4 Centro de Estudos Históricos da Lourinhã, Lourinhã, Portugal Keywords: Augmented reality · Indoor positioning · GPS · ARKit · Digital cultural heritage 1 Introduction and Background The employment of Augmented Reality (AR) in museum exhibitions and at cultural heritage sites has increased dramatically over the past decade (Bekele et al., 2018). AR as a mode of representation and reconstruction is used to extend and enrich the experience of artifacts on display thus providing important context and quality to the objects and environments observed (Gimeno et al. 2017). AR applications in various forms are also frequently found as part of cultural heritage locations and archaeological sites in the open air (Vlahakis et al. 2002; Litvak et al. 2020). Employment of Augmented Reality (AR) in indoor Museums requires adequate positioning precision in environments with complex room structures, including rich inventories, and with visitors constantly changing between still positions and movement, individually as well as in groups. Quests for the simple yet solid indoor positioning systems (IPS) for off–the–shelf mobile devices to master these diverse conditions have been ongoing for years (Lymberopoulos & Liu, 2017), though with limited progress. More recently we have seen improvements with the launch of ARKit – Apple’s solution for iOS (iPhones) and iPadOS (iPads), and ARCore – Google’s solution for Android OS (Oufqir et al. 2020). These approaches combine camera input for image recording and recognition, focus measurement and, eventually, the use of built–in LiDAR scanning. Mobile applications employing Global Navigation Satellite Systems (GNSS), better known as ‘GPS’ (Global Positioning System), have always been considered the outdoor only solution for localisation, and for good reasons. Every smartphone user has expe- rienced the drastic decrease in positioning precision as the receiving terminal is moved © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 M. C. tom Dieck et al. (Eds.): XR 2023, SPBE 2024, pp. 161–172, 2024. https://doi.org/10.1007/978-3-031-50559-1_13