## 2 Similar Works
### Identifying State-of-the-Art Software  
Prior to identifying related state-of-the-art software, this section addresses the scientific-technological areas involved in applications pertinent to the presented work. These areas are characterized by strong synergies between pure computer-graphics and animation-motion technologies with AR and MR technologies. In addition, AR software applications cooperate closely with geospatial software, in order to inherit LBS and GIS capabilities. Therefore, (a) animation-motion, (b) GIS functionalities and (c) VR-AR-MR comprise the three major software areas of interest relevant to the presented work. Another difficult task was to classify the findings of this review according to their general software type, e.g., API, framework or library; however, such a classification would cause misunderstandings and non-logical comparisons. Besides, many terms may have similar meanings. Having gathered as much information as possible, a decision was taken to split the final table in three subdivisions based on the distinct contribution of the findings, as follows:  
1. Game engines: Their role in 2D and 3D graphics rendering, physics simulation, interactive animation and motion effects is decisive to place them as head of the related software table. Beyond the features recording support of the previously defined technological areas, the capability of acting as an authority tool is also recorded and their capability to operate on a browser. 2. Libraries-platforms-prameworks: They were created to cover a broad range of functionalities, including basic geospatial ones, and graphics animations, and to cooperate with other software components to form complete solutions. This category records the same features as the above category. 3. AR tools: This subdivision contains software exclusively focused on AR that is obviously cooperating with software from the above categories to form complete solutions. Some AR-specific, individual features were selected such as simultaneous localization and mapping (SLAM), Geo-location, 2D and 3D images recognition and online-cloud recognition. Before presenting the findings of the review, a brief presentation of some of them from each category is offered below. Unity is a real-time 3D development platform that lets artists, designers and developers to create immersive and interactive experiences, in games, films and entertainment, architecture or any other industry. As of 2018, Unity had been used to create approximately half of the mobile games on the market and 60 percent of augmented reality and virtual reality content [33]. Unreal Engine is an open, advanced real-time 3D creation tool that is continuously evolving to serve as a state-of-the-art game engine, giving to creators, freedom and control to deliver cutting-edge content, interactive experiences and immersive virtual worlds [34]. These two engines seem to be the leaders in the field of game engines and a very recent article attempts to compare them [35]. CityEngine is an advanced 3D modeling software for creating expansive, interactive and immersive urban environments that may be based on real-world GIS data or may showcase a fictional city of the past, present or future. CityEngine fully covers all critical geospatial aspects, such as georeference, geolocation and overlaying; however, it does not integrate motion effects on spatial objects [36]. On the same category, vGIS Utilities is a cloud-based app that displays GIS and CAD data, using mixed and augmented reality. It does not require specialized hardware or client provided servers to operate. It connects to Esri ArcGIS and other data sources to aggregate and convert traditional 2D GIS data into 3D visuals. It primarily targets public utilities, municipalities and service providers [37]. Cesium.js is a geospatial visualization framework for 3D mapping on the Web. It is built on top of WebGL, is HTML5 standard, supports industry standard vector formats (KML, GeoJSON) and is open source and cross-platform.