For example, this picture structure
Is it possible to consider the form obtained by using a single line as the model direction guided by the model?
Adding an extra circle in the top curve will give what you need. Without that the loft will take the straightest way up.
Thank you for your guidance, but it’s not what I want. What I hope is to finalize the design by the line-guided model. The significance of this is that I can consider making many shapes I want, instead of rigidly adjusting the shapes obtained after moving and estimating the placement. In fact, if developers can consider this convenient way, it will be the friendliest for designers (if it can be realized, I can import foreign linetypes to assist in modeling).