The calculation formula of arc length is a mathematical formula, L=n× π× r/ 180, L = α× r ... where N is the degree of central angle (angle system), R is the radius, L is the arc length of central angle, and α is the degree of central angle (arc system).

In the construction and installation site, we often encounter circular linear shapes, such as circular structures or decorations in highways, railways, water conservancy, electric power, building construction, municipal landscape engineering, etc. Where there is construction, almost circular alignment is needed. It can be said that how to realize accurate circular arc fixed-point lofting is a problem that every field technician must face.

By analogy, three kinds of five common arc lofting methods are summarized. Among them, it is the first time to systematically summarize and put forward two kinds of straightedge methods for arc lofting in workplace. Its advantages are intuitive, simple and easy to operate. Construction workers with junior high school mathematics knowledge can check and recover their shortcomings at any time with the simplest ruler, which is worth popularizing and applying.