The traditional surveying and mapping instruments, It had been mature development ,for example total station, electronic theodolite, levelling instrument , etc.
In effect, transform the surveying and mapping instruments into small laser kind of instrument.
Nowadays, more and more field needs to be the level of the noncontact or plumb datum as a reference, such as architectural decoration, water conservancy and hydropower.
At present crossline Laser is popular a new instrument on the market, This instrument can export a horizontal and vertical laser line. It is now come into widespread use in the ceiling construction, water and electricity, indoor decoration, pipe etc.

The working principle of crossline Laser is simpleness , Generally it can export a horizontal and vertical laser line in any plane that must work within the scope.
The general basic structure as shown in figure 1. Laser and cylindrical lens is together, the laser beam be exported by laser, The laser beam and Cylindrical lens is basically vertical. Pendulum ensure that laser and cylindrical lens of whole is lead the state of vertical.
the cylindrical lens vertical plane as example to explain：We took a cylindrical lens of a level profile  A1′A2C2C1′as shown in figure 2. Light rays pass through cylindrical lens that take place two times refraction of cylindrical, the light A1A1' and 'C1C1 can be split into A2A2' and a light C2C2', Through the circle of light B1B1' that spread direction is invariant, the light B2B2 'and light B1B1' had same direction after they were exported. In this we define B1B2' direction that is the main direction of crossline laser. So a horizontal beam is expanded into a horizontal plane，because Lead hang on the direction of the beam is normal incidence , The interval is unchanged between different profile, the beams not be expanded. At this time a front of crossline laser  have a level line of laser.