# VR as a 3D Modelling Tool in Engineering Design Applications
## 2 Methodology  
The research consists of two user studies, a preliminary study that helped us set the study foundations, and the research study in which the applicability of VR technology was investigated. First, the preliminary study was conducted to define how to evaluate the performance level of the CAD modelling steps since desktop modelling cannot be directly compared with VR 3D modelling. Previous studies determined that conceptualizing using VR is faster compared to using the desktop tools [2; 32], therefore, to determine if this also accounts for building the 3D models, the information on the timing and problems encountered was obtained in the studies. After the desktop CAD surface modelling test, where the evaluation criteria were established, the research study was conducted with VR 3D surface modelling, investigating the capabilities of the VR modelling tools using HMDs to support the design process from concept to solid model. Points of interest were: ease of use of tools and controls, geometry generation capabilities, insertion of reference images, combining surfaces, detailing, dimensioning, geometry exploration capabilities, conversion to a solid body.  
The methodological framework of the studies is explained in Figure 1. A user test was conducted in both studies, while the research study was conducted using a focus group method in order to obtain more detailed information. In addition to the user test in the research study, observations and three questionnaires were made: before, during and after VR 3D modelling.  
The participants in both studies were tasked with capturing the design intent from sketches. This task was chosen as our aim was not to test the user creativity when using the tool but to study whether the VR technology is capable and accurate enough for engineering applications in later product development phases.  
The 3D modelling process (the embodiment design) in both studies was tested by using a preselected 3D object. A computer mouse (Figure 2) was chosen to be modelled, due to its suitable level of geometrical complexity. The criteria for object selection were organically (e.g., freeform) shaped surfaces. The features of interest were transitions, fillets, and curvatures that occur between two surfaces. Achieving adequate quality of surfaces and the possibility for the transition from a surface model to a solid model were studied in detail.  
The participants' models in both studies were evaluated based on the criteria defined by researchers in the preliminary study according to known steps in the workflow of capturing the design intent. The key steps for creating a freeform 3D model from a reference image were adopted from [37], based on which criteria and quality indicators of the modelling outputs were established (Table 1).  
Figure 1: The methodological framework.  
Figure 2: Isometric image of the reference mouse.  
Zebra striping is used in computer graphics to visualize curvatures on smooth surfaces and is thus a diagnostic shading technique [38]. Curvature continuous surfaces show as smooth flowing stripes, whilst broken tangency displays as an abrupt change in the direction of the stripes [39]. Curvature combs are graphical elements associated with 3D modelling software that indicate the degree of curvature at a particular point on an element. They are used to predict problem areas in sketches, especially splines used to create complex surfaces [40].