# AR in the Architecture Domain: State of the Art
## 6 AR Development Tools
### Commercial SDK  
The most used and best known multipurpose commercial SDKs, not devoted to the architecture domain alone, are Layar, Wikitude, and Vuforia (Table 2). Layar is the most widely used AR-SDK for service localization; it can store POIs in a remote database (DB) and retrieve the associated information based on the user's position, using the Blipparaugmented reality SDK to enable quick and easy mobile AR development. These features make this kind of application ideal for outdoor wayfinding applications and experiences in architecture and urban planning [5] and create a framework for architecture and building engineering education [152]. Wikitude is a platform released in 2008 that leverages both location-based and vision-based tracking. For the latter, it supports images and 3D model recognition. The generation of 3D-model-based targets is currently in beta version (SDK 7), but from 2017 it introduced SLAM technology and instant tracking, working with three-dimensional structures and objects. An interesting application for partially damaged or destroyed buildings to help visitors interact with the city's monuments is offered by [49], using this geo-localization to interact with archaeological sites [153]. After removing Junaio (Metaio) from the market, Vuforia has become the most widely used toolkit for most developers. Its simple integration with Unity3D allows the visualization of refined 3D models, and a quick and easy cross-platform development. It supports various 2D and 3D target types, including image targets, 3D multitarget configurations, and a form of addressable fiducial marker known as VuMark. The author of [154] presents a framework for visualizing 3D artifacts with Vuforia in archaeology, while [155] explains the systematic structure, recognition of the target library, and the working process of the virtual exhibition hall system. At the urban/landscape scale, [156] suggests an application, while [157] proposes the visualization of interpretative 3D models, and [158] proposes an AR BIM-based application. Furthermore, some additional applications are implemented in the architecture domain. One is Maxst, a powerful AR-SDK system that combines virtually enhanced physical reality with AR (augmented reality), AI (artificial intelligence), and computer vision technology. MAXST provides various solutions, supported by VPS (visual positioning service), to define the user's location by constructing a 3D spatial map for both in/outdoor AR content creation, instants, objects, QR codes, images, and marker trackers, VisualSLAM, and Cloud Recognizer. An application related to interior design and planning architecture furniture can be found in [159]. Moreover, there are several AR-SDKs designed to support architecture design and visualization. One strictly connected to Autodesk is AkulAR, allowing the user to experience 3D digital models at real size, geo-located in the real world, using only a smartphone or tablet. IN2 AR is a non-new ActionScript3 and Adobe Native Extension Library or Unity3D plugin that detects images and estimates their pose using standard webcams/cameras or mobile cameras. The pose information can place 3D objects and videos onto the image for AR applications. Augment supports the AEC domain with easy configuration; it is based on the Vuforia augmented reality SDK and OpenGL. Meanwhile ARki is a real-time AR visualization service for architectural models, which incorporates AR technology into architecture by providing 3D models overlaid onto existing 2D floor plans, with multiple levels of interactivity for both design and presentation purposes; it includes real-time shadow analysis and material selection.