Speckle is the fundamental uncertainty factor in laser triangulation. A method to simulate the speckle in rotationally symmetric triangulation was presented and the simulated image was obtained. In this kind of triangulation sensors

the incident laser point will be imaged to a ring on the detector and the speckle is accordingly arc shaped. Properties of this kind of speckle were studied. The speckle size in radius direction of the ring obeyed the subjective speckle

and is determined by the number aperture of the optical system. In tangent direction of the ring

the speckle is essentially an objective speckle

its size is determined by the optical path length from the object to the detector

the area of the incident laser spot

as well as the radius of the imaged ring because of optical path was folded. Experiments showed that the simulation result was coincident with speckle theory. Based on the simulation

an analysis of the uncertainty limits of rotationally symmetric triangulation sensor was given. It shows that using the optical layout in our sensor

an uncertainty about 1/5 of traditional triangulation was estimated with same optical system numerical aperture and grey centroid algorithm.