The most obvious mathematical method in window grillage is the central symmetry method, which is also one of the commonly used forms of traditional paper-cutting.

Central symmetry refers to rotating the figure around a certain point 180. If it can coincide with another graph, the two graphs are said to be symmetrical or centrosymmetric about this point.

Central symmetry refers to the (positional) relationship between two figures. The symmetry points of the central symmetric graph are on these two graphs respectively.

Regarding central symmetry, it has the following characteristics:

(1) is used for two graphs.

② refers to the (positional) relationship between two graphs.

(3) The symmetry points of the central symmetry graph are on these two graphs respectively.