# Towards the Evaluation of Augmented Reality in the Metaverse: Information Presentation Modes
## 3 The Desktop-Simulated Testing Environment (DSTE)
### Three-Dimensional Interaction in the DSTE  
To accomplish the assembly task, users interact with LEGO bricks through the following actions:  
* Picking the assigned brick;
* Rotating a piece before putting it in place;
* Assembling a brick on the plate or on other pieces;
* Disassembling a brick (e.g., wrongly placed);
* Changing the point of view. For each of these actions, we defined interaction metaphors in the DSTE following other UIs (e.g., Virtual Reality testing applications [35] and videogame GUIs) so that they would appear familiar to users. **Picking. ** Users can pick a single brick to place on the plate by clicking on the corresponding picture in the top-left corner of the interface, as in [35] (see Figure 3a), and then a 3D preview of the LEGO brick chosen appears on the GUI in the position of the mouse cursor (see Figure 3b). We decided to simplify this interaction from its homologous counterpart in true AR by not inserting the 3D models of the picking bins in the virtual environment. The main reason for this choice is that our testing environment is not aimed at evaluating the picking task. For the same reason, we showed only pictures of the bricks that are used in the LEGO set. As shown in other works [40,41], the proposed interaction metaphor allows users to focus their attention only on the assembly task and on the different types of instructions without the risk of decreasing their performance due to the picking task. **Rotating. ** When users pick a LEGO piece, they can also rotate it, clockwise or counter-clockwise, by pressing the keys \"D\" and \"A\" on the keyboard, respectively (see Figure 4). Every time users press these keyboard buttons the picked brick rotates 90 degrees in the corresponding orientation. The change in angle takes place instantaneously without animations. No other rotation axes were considered because the assembly can be performed only along the vertical direction. **Assembling. ** When users understand where to place the LEGO brick, they can release it by clicking on the desired location. The application has been designed in such a way that it allows users to automatically attach the picked LEGO brick to the LEGO Duplo plate or to another placed brick, avoiding unintentional interpenetration. Our assembly action is intended to maintain naturalness and intuitiveness, but it is also simpler and faster than assembly actions proposed in other works [13, 14, 15, 16], in which complex devices were used  
Figure 2: A user while carrying out the experiment with our DSTE at home (**left**); interface of the proposed DSTE (**right**): simulated AR instruction is provided through an auxiliary model used as a world-fixed visual asset 1�, and a drawing used as a screen-fixed visual asset 2�. to simulate real gestures. In this way, it is possible to avoid technical issues in the software physical simulation, such as the unpredictability of virtual object behavior, collision, and attaching [11]. **Disassembling**. If users make a mistake, an \"undo\" button allows them to remove the last piece that they wrongly placed. The \"undo\" button is placed on the top of the interface, and it allows the user to instantly remove the LEGO brick that needs to be disassembled (see Figure 5). Additionally, this interaction metaphor is much more simplified than its homologous counterpart in true AR, neglecting all physical aspects that do not concern our study. **Changing the point of view**. A slider on the GUI allows participants to rotate the camera to change the point of view (see Figure 6). The action of the slider simulates the relative rotation between the user's head and the LEGO plate in true AR. Users have to hold down the left mouse button on the slider and move the cursor in the direction in which they want to change the view. In the editing phase, the test designer can choose the most suitable parameters for natural usability, such as the rotation speed of view and the main camera field of view and orientation.