# VR as a 3D Modelling Tool in Engineering Design Applications
## 2 Methodology
### Research Study: VR 3D Modelling Study
#### 2.2.1 VR 3D Freeform Modelling Steps  
VR 3D freeform modelling can currently be achieved with NURBS surfaces or subdivision surfaces. However, good surface transitions and merging of surfaces in VR modelling can currently only be achieved with subdivision surfaces. Therefore, they were used as they preserve the curvature continuity across the entire shape. \begin{table} \begin{tabular}{c c c c c c c} \hline \hline
**Key Steps** & **Imported Images** & **Sketches** & **Surfaces** & **Geometry** & **Surface** & **Solid Body** & **Details** \\ \hline \multirow{3}{*}{**Criteria**} & Importing, scaling, & & & **Matching** & **Transitions** & **Solid body** & **Split surface** \\  & and placing of & & & **Surfaces** & **The required** & **the mirror** & **the mirror** & **cration.** & **and mouse** \\  & & & & & & & \\  & are needed. & & & & & & \\ \hline \multirow{3}{*}{**Quality indicators**} & \multirow{3}{*}{Visual indication} & Visual & Mesh preview. & Visual & **Zebra * stripes.** & **Software * & Visual \\  & & & & & Volume and mass data. & combs. & readout. & **risation.** \\ \hline \hline \end{tabular}   
* *The process of modelling using VR tools can be split into distinct phases, similar to desktop modelling. Considering that the goal was to create a model according to the images, some precision is required. Sketching of the rough outline could be omitted in VR; however, it is often useful to capture the geometry as best as possible. One of the critical points is to achieve a solid body. As the VR tools enable only the export of meshes, it needs to be later converted. The detailing can also be done after the conversion. One of the important key features identified in the participant study was the ability to capture the desired shape. To achieve this, the reference images need to be placed on appropriate planes and scaled to a suitable size. The VR tools achieve this by snapping the images to the planes and by incorporating accurate measuring tools to scale the images. Some tools enable the snapping of images to the middle point of the image. If the images are prepared with care, this can enable very accurate positioning and alignment. A 3D view with a bounding box can be included to depict the shape more accurately. The modelling can then be continued by directly creating the surfaces. However, sketching a rough outline can sometimes be useful. The sketch also includes control vertices (CVs), to which the surface CVs can be easily snapped to later. Firstly, a sketch is created, then the users can position themselves to a certain projection and move the CVs in an XYZ direction to accurately match the reference images. This ensures that the desired shape is achieved. The most important key feature identified in the participant study is creating the surfaces. Design guidelines need to be considered when creating the surfaces. These include: the fewer control curves and control vertices the better; be mindful of the transitions between the surfaces; when translating the mesh to CAD, be mindful of the mesh accuracy; when aligning surfaces, they need to have an equal number of CVs; create surfaces where the angle of the corners is as close to 90\({}^{\circ}\); and try to create four-sided surfaces. It is possible to create only half the model and mirror it over the mirror plane. This ensures a tangent transition over the mirror plane. The detailing can be executed in the VR or desktop environment. However, when creating a model for design review in VR, it is faster to create it directly in VR tools. One of the key features of modelling in desktop applications is to achieve a solid body, which is later used in downstream processes. Current VR modelling tools do not enable the export in formats for solid body modelling. If this would be ensured, the VR modelling would be even more compelling to engineers. However, the design can be exported in a mesh file (Figure 3I), which can be converted to a solid body with many tools.