What are the ways and means of sketch modeling?

There are two main ways of sketch modeling: 1, which is based on the expression of light and shade. 2, structure sketch's way of expression.

The expression of light and shade is the expression of the relationship between light and shade of objects, and the most essential problem is the relationship between black, white and gray under the action of light. Good at expressing body size, space, texture and weight.

Structure sketch's way of expression is to take lines as the main means of expression and pay attention to the internal structural relationship between objects and images. It excludes the intuitive light and shadow phenomenon and studies the physical structure of objects expressed by lines with different rhythms.

There is also a way to express objects by combining lines and surfaces.