In this article considerations are presented concerned with principles of woven fabric 3D structure formation, by warp and weft yarns acting upon each other and by certain forces. The cross-section structure, as well as the shape, is a complex problem dependent upon forces, geometry, material properties, and time. An exact theoretical analysis is problematic. Different models described in literature are discussed and few examples of assumed cross-section shape (circle, ellipse) are presented. The author finds, based on his own calculations as well as on results of measurements, that the cross-section shape can be simulated by lens. Not all analysis are satisfactory - an example with too large deviations is presented. As a continuation of previous investigations a computing method was developed which enables one to investigate the limiting values of yarn crimp and to conduct studies into fabric structure parameters.