https://phys.org/news/2018-07-d-air-scaffolding.html

To fill in these missing links during the conversion, 3-D sketching techniques are under development. They would help designers naturally provide missing 3-D shape information in a 2-D drawing. For example, if a designer draws two symmetric curves from a single point of view or draws the same curves from different points of view, the geometric clues that are left in this process are collected and mathematically interpreted to define the proper 3-D curve. As a result, designers can use 3-D sketching to directly draw a 3-D shape as if using pen and paper.

Among 3-D sketching tools, sketching with hand motions in VR environments has drawn attention because it is easy and quick. But the biggest limitation is the design cannot be articulated solely via rough hand motions, and are thus difficult to apply to product designs. Moreover, users may feel tired after raising their hands in the air during the entire drawing process.