The basic elements of sketch modeling are five key words: sketch modeling 1 physical form is the external form of objective objects in space. Any object is different from other objects because of its specific physical existence. Form belongs to the basic basis and constant factor of sketch modeling. We can also decompose the understanding of form into two factors: shape and volume. Appearance refers to the visual external image of the plane; Volume refers to the three-dimensional volume of space. In sketch, the two have their own independent meanings and values, which complement each other and are inseparable. Form is the external image of volume, and volume must be tangible to reflect it. Therefore, we can also understand form as a shape with volume. In other words, among the sketch modeling factors, our understanding of form should establish the concept of three-dimensional space. Any complex shape can be summarized into several basic geometric shapes, namely, cube, sphere, cylinder and cone. In our daily life, more objects and images are composed of various geometric shapes in different forms. When we observe an object image, we should first pay attention to its basic shape as a whole. The basic shape of the object image is different, so the physical characteristics of the object image will be different. The basic shape is the relationship between an object and an image. Grasp the basic shape of an object, and then grasp its physical characteristics. Accurately grasping the physical characteristics of object images will lay the foundation for sketch modeling. Structure sketch's form mainly refers to the external characteristics of objects, while structure mainly refers to the internal structure and combination of objects. Form and structure are the relationship between appearance and connotation. Structure is the internal basis for the formation of foreign trade of objects. Without understanding it, it is impossible to accurately grasp a series of external characteristics of objects. In sketch, structure includes two aspects: one is anatomical structure or constituent structure; The second is the anatomical relationship between human body and animal bones and muscles, that is, anatomical structure. Familiarity with anatomy is the basis of role modeling. The internal composition frame of other objects and its composition relationship are called composition structure, which is the internal foundation of similar objects. Grasping the structural relationship of objects in painting mainly lies in reflecting their basic physical characteristics by surface, which is convenient for understanding and grasping the complex structural relationship and is conducive to shaping the image volume. The concept of structural materialization is called physical structure or geometric structure. Stereo is a collection of faces, and it is the basic viewpoint of modern painting to express stereo and space. Therefore, the grasp of three-dimensional image in sketch usually begins with facets, which is a generalization of objects and shapes and an analysis of structures. The generalization of surface constitutes the three-dimensional framework of object image. Circular or nearly circular shapes can also be shaped by generalized surfaces. The square surface can more accurately grasp the overall relationship of the circle. The so-called modeling is to shape the three-dimensional image roughly and accurately. Modeling factors such as the structure and shape of scale object images must be related to a certain scale in appearance, and different scale relationships are proportional. The forms of any object are connected according to a certain proportion. If the scale changes, the shape of the object image will be marginal. Therefore, the mistake of basic proportion will inevitably lead to the mistake of understanding and expressing the structure and shape. In the initial stage of sketch, the significance of proportion is particularly important, and the accuracy or inaccuracy of picture image is often caused by the correctness of proportion relationship. The concept of proportion in sketch can also refer to the proportional relationship between objects and images; Proportional relationship between parts and whole, parts and parts in the same object; The light-dark ratio of hue, etc. The observation of body proportion should not be a mechanical and rigid comparison, but should pay attention to the proportional relationship and perspective changes of three-dimensional objects at a certain angle. In comparison, we should pay attention to the proportion of objects and images, especially the proportion of large images and whole images, and should not stay in the proportion of local details. Beginners can get the accuracy of the basic proportion by means of tool measurement. With the improvement of observation ability, we should gradually abandon this method and pay attention to training the accuracy of observation ability through feeling, eyesight and comparison. 4 perspective the spatial phenomenon of natural objects that we see is the perspective phenomenon. Using scientific principles and methods, the perspective phenomenon is accurately shown on the screen, and its image, position and space feel are the same as the real scene, which is painting perspective. In sketch, the application of perspective is to determine the depth of the object on the picture, that is, the spatial position of the object and its parts in the picture, which is the basic factor to express the three-dimensional effect of the object and create the spatial effect in painting. Therefore, the perspective rule is an important basis for realistic modeling, and mastering the basic principles of perspective is the basis for accurately observing and truly depicting the spatial relationship between objects and images. Perspective is a complex science. Here are some simple introductions. The position of the painter's eyes, the line of sight between the viewpoint and the object. After the viewpoint is fixed, the range seen from the horizon from a 60-degree perspective is a horizontal line with the same height as the viewpoint. The relationship between the visual field and the image: see the bottom above the visual field, see the top below the visual field, and the visual field is in the middle of the object image, so you can't see the ground or the top. When a plane in front of the Parallel perspective figure is parallel to the picture, the perspective relationship between the object and the image is Parallel perspective. Parallel perspective can see at least one face, but at most three faces. All the edges of the body at right angles to the picture have disappeared. The emphasis is on perspective. One side of the body is parallel to the ground, and its elevation forms a certain angle with the picture, which is called angle perspective. Angle perspective can see at least two faces, and the edges extending to the depth of the picture disappear at the left and right points respectively. Light and shade is one of the basic elements of sketch and an important factor to describe the stereoscopic and spatial effects of objects and images. Any object will show a certain relationship between light and shade under the irradiation of light. The intensity of the light source, the distance from the light source and the different illumination angles will make the image of the object show different brightness. Light is a prerequisite for the formation of light and shade of an object, and it is also an external factor for the change of light and shade of an object. When an object is illuminated at a certain angle, it will produce two contrasting and interrelated light and dark systems: the light receiving part and the backlight part. The light and shade level of an object can be summarized as three facets and five tones, which are connected into a unified whole with a certain color level relationship, which is the basic law of light and shade change. In a certain light, the change of light and shade is caused by the ups and downs and rotation of the body. Therefore, light and shade only belong to a specific physical structure at any time, and the tone change of light and shade is to show the ups and downs of the structure. Structure is an internal and essential factor, and light and shade is an external and concrete form; The physical structure needs to be represented by light and shade, and the relationship between light and shade reflects the inherent physical ups and downs and structural changes everywhere. Light and shade are not only the three-dimensional sense of the image, but also the main factor to show the overall spatial effect in the picture. The treatment of light and dark levels and the contrast between reality and reality are the basic means to show the spatial relationship and overall atmosphere of the five spices before and after.