High Precision 3D Traverse Established by Trigeminy Total Station Method

  Objectives  To meet the precise coordinate transmission requirement of underground engineering, a measuring and data processing method of high-precision 3D traverse is inspired by the trigeminy tripod method.

  Methods  The trigeminy total station method is proposed to build 3D traverse. The U buckle is used to fix the adapter of tooling ball reflector on the handle of a total station. The spatial relation between the tooling ball reflector center and instrument center is calibrated to correct the observed values. The lines connecting each two instrument centers constitute a 3D traverse, which avoids the manual measuring error of instrument height and prism height. A practical model for unparalleled plumb lines correction and Helmert variance component estimation are applied to determine the weight of different class observation. These improvements make the data processing of 3D traverse more rigorous.

  Results  In a tunnel surveying project, a closed 3D traverse is established with 15 sides. Compared to traditional adjustment method, the variance of unit weight of the proposed method is obviously decreased after correction for unparalleled plumb lines and variance component estimation. The precision of traverse points is obviously improved and better than ±0.5 mm. Digital industrial photogrammetry system is utilized to check the adjustment results. The precision of common points transformation between the survey results of digital industrial photogrammetry system and that of 3D traverse is ±0.32 mm.

  Conclusions  The proposed method has a good performance in severe conditions such as short sides and large vertical angles, so it is worthy of popularization and application.