1, three views: refers to the graph drawn by the observer observing the same spatial geometry from three different positions. Three views are the front view, top view and left view.

2. The view can only reflect the shape of the object from one direction, but can't completely reflect the structural shape of the object.

3. The length of the front view and the top view should be equal, the height of the front view and the left view should be equal, and the width of the left view and the top view should be equal. Three views are the result of projecting the same object from three different directions. In addition, there are sectional views and semi-sectional views as AIDS, which can basically express the structure of the object completely.

5. Three-view drawing methods: long alignment, high alignment and equal width.

6. Three views of several common geometric bodies: the front and side views of the cylinder are rectangular, and the top view is circular; The front and side views of the cone are isosceles triangles, and the top view is a circle and its center; All three views of the ball are circles.

7. In other words, the front view is a view of the projection plane from the front; The side view is a view from the left to the projection plane; The top view is a view from above to the projection plane.

8. The three views of the assembly should understand the structure, decompose the assembly into basic geometric figures, and then draw according to the basic geometric figures, paying attention to the position and size relationship of the three views.