Abstract
This paper presents our experimental studies on sketching behaviour, processing and individual preference through questionnaire and sketch observation. This study has been carried out to obtain the barebones criteria that will be adopted to develop a free-form surface modelling system from on-line sketching. The results show that some dynamic sketching information, including certain visual forms such as form lines, reference lines, grid lines, shades, shadows, and/or annotations, etc., should be included in a sketch-based modelling system.