## 2 Materials and Methods
### The AR Application  
The museum AR Android application, which can be downloaded from the museum website on the visitors' mobiles or tablets [48], enhances the visitor experience. The application was developed as a result of three bachelor theses produced by [PERSON] in 2018 [49], [PERSON] in 2019 [50], and [PERSON] in 2021 [51]. Using the application, the visitors do not just examine the museum pieces as objects; they know more about their history and understand how the items work and were used. AR produces curiosity, and the visit becomes more pleasant and didactic.  
The application uses AR reference targets that are on the museum showcases. The target should be in the proper position in relation to the object to avoid obfuscating it and to allow for presenting the multimedia content in the correct position. The target size is selected considering that the visitor device should detect it at an adequate distance from the observed object. The multimedia content will be shown on the user device display around or over the museum item. Figure 1 presents an example of a target inside the museum.  
Before developing the application, an analysis of the different needed multimedia contents was performed. First, a list of the museum objects to be enhanced with AR multimedia material was created. Various aspects were considered in selecting these items: the list should include objects from all the museum sections, the selected items should be very representative in their sections or have a non-obvious functionality or a fascinating history that could be shown. Second, the multimedia content and how it would be displayed for each item was decided and produced. The content can be audio, video, or interactive images and can be displayed next to or over the object.  
The application was developed using the cross-platform 3D game engine Unity 2020.3 together with the AR software development kit Vuforia 8. Unity is an integrated design environment that can be used to create 3D graphic mobile applications, and Vuforia adds to Unity several tools for developing AR mobile applications. Vuforia includes several 2D image and 3D object recognition tools. It also allows the creation of your own AR targets that can be identified more precisely. Vuforia tools, using the device camera-captured image, sends real-time target detection, identification, and tracking (positioning in space and orientation) to Unity. Using this position and orientation, Unity shows multimedia content oriented in space in real-time on the device display. Unity also allows for programming different interactions with the displayed multimedia content. So, this content can be modified through tactile buttons represented on the user display. Figures 2 and 3 show two different interactive content examples. The first content is shown over an original source of a Lenna standard test image of the image processing field. Users can modify the image by showing different image processing methods. The second content is shown over an original 1930s telephone switchboard, where users can select operators from ancient times.  
At the museum, there are old artifacts not in use, AR allows us to understand how they work. As an example, Figure 4 shows a video describing how an 1888 gramophone works next to the historical item.  
Figure 1: AR target of the 1964 Akai magnetophone.  
Figure 3: 1930s switchboard AR interactive content.  
Figure 2: Lenna interactive AR object: (**a**) applying black and white image processing; (**b**) applying negative image processing.  
The application works on any device with Android version 4.0 or higher.