## 4 Design, Development, and Implementation
### Setup Levels  
To conduct the simulation, the experience was designed across two levels: Level 1--Tutorial; Level 2--UAH Model. Figure 7 shows the components of each level, the outputs generated, and the parameter evaluation methods.  
In Level 1--Tutorial, the user has an initial interaction with the virtual reality components (controllers, headset, and synthetic hands), as well as with key elements representative of a universally accessible housing (UAH) unit in the simulated environment. This level is intended to help the user become familiar with the functionality and use of the VR tool. The tutorial is divided into two stages: a welcome lobby and a general walkthrough. In the first stage, the user is seated in a real wheelchair and wears the VR  
Figure 6: Scenario modeling. (**a**) UAH master bedroom plan view and 3D perspective view, (**b**) UAH bathroom plan view and 3D perspective view, (**c**) UAH living–dining room plan view and 3D perspective view.  
Figure 7: Virtual reality VR experience design diagram.  
headset. The experience begins in a virtual welcome lobby that includes visual guides (illustrative panels) explaining how the controls work, an interactive light switch, and a start button that transports the user to the main simulation map where the evaluation will take place. At this point, users also receive general guidance about what they will encounter and what is expected during the experience. The main objective of this stage is to assess whether the user understands the basic functioning of the VR system and how to navigate and interact within the environment. The second stage consists of a guided walkthrough of the virtual home, starting from the exterior and moving through each room. During this tour, users can observe the furniture and fixtures with which they might collide or interact, helping them become familiar with the space and understand the controls and interaction mechanics. It is important to note that, during this phase, interactions with elements related to the UAH parameters are not yet enabled, as the goal is purely spatial recognition. At the end of this stage, a text file is generated to build a heatmap that records the user's position every 3 s. These data highlight key areas of interest and help interpret user behavior within the environment.  
In the Level 2--UAH Model, the user must move through the space, interact with objects, and perform specific maneuvers related to the previously defined accessibility parameters. To guide this process, the user receives instructions or \"missions\" such as turning on light switches, opening doors, or moving to certain rooms. In addition, the user is free to explore and interact with all available elements, further enhancing immersion and natural engagement with the environment. Evaluation in this level is based on the use of heatmaps, collision counters, and detailed tables recording which elements were collided with. These tools help determine the complexity of maneuvers and the functional accessibility of the environment.  
The experience was designed so that the user follows the path \"without realizing they are evaluating the design.\" Tasks are structured with hidden objectives --namely, evaluating the design's accessibility parameters-- but are presented as natural in-context actions, avoiding overt instruction. This approach strengthens the sense of immersion and supports a more spontaneous and realistic evaluation. Figure 8 summarizes the stages of the VR experience.  
Figure 8: (**a**) Level 1 tutorial level scenario, (**b**) Level 2 UAH model scenario with environments; (**c**) instruction label in Level 2.