First, the definition method
It refers to the method of making a straight line perpendicular to the edge in two planes through any point of the edge of dihedral angle, and then the angle formed by these two straight lines is the plane angle of dihedral angle, and then calculating the plane angle in the plane.
Two or three vertical lines method
It refers to the method of constructing the plane angle of dihedral angle and then calculating the plane angle according to the idea of "perpendicular to the projection and then perpendicular to the diagonal line".
Third, the vertical surface method.
It means to cut a dihedral angle with a plane perpendicular to the edge, then there must be two intersecting lines between the two faces of the section and the dihedral angle, and the angle formed by these two intersecting lines is the plane angle of the dihedral angle, and then the plane angle is calculated.
Fourth, the area projection method
The so-called area projection method is to calculate the dihedral angle by using the cosine value of the dihedral angle whose projected area is equal to the original area according to the relationship between the figure and its projected area on a certain plane. This method is usually used for dihedral angles without edges.
Five, the normal vector method
The normal vector method is a method to find the dihedral angle by finding the angle formed by two vectors perpendicular to the dihedral angle, and then using the equal or complementary relationship between this angle and the plane angle of the dihedral angle. (How to judge equality or complementarity will be announced in the near future. )
Six, vertical line method
It means that the vertical foot is determined by the undetermined coefficient method first, and then the dihedral angle is calculated by the formula.