How to get to the center line in SOLIDWORK

2. In the sketching interface, click the straight line, and the second one is the center line. Please accept it.
thank you

3.

1. As shown in the figure below, open SolidWorks software, click "open", then find the saved drawing file, and click "open"

9. As shown in the figure below, the center line is added successfully, and the drawing is no longer lack of center line

4. Unknown_Error

5. Menu insert comment center line, and then select the circle or arc you want to mark

6. After selecting the line, the properties dialog box will appear on the left side, and you can find it in it as the reference line

7. Unknown_Error

8. View, point "temporary axis"

9. This requires certain skills, such as the following:
1, make an axis, cross the coordinate center, and constrain to a point on the circle
2, delete all the parallel / vertical / relative constraints in the circle
the center of your circle has been constrained to the datum plane
3, the dimension can only be marked between the grass circles, not to the datum plane or coordinate
4, the angle between the final axis and the datum plane
after changing the included angle, the whole circle will move without any deformation
(this is the basic principle of folding mechanism) or
1
2. The diameter of the dashed circle and two vertical dashed lines in the figure below are the construction lines
3. The driving angle is the angle between one of the diameters and a datum plane.