为了适应海上应用并降低经纬仪坞内标校成本，采用恒星位置代替固定方位标，将原本在坞内的标校工作转移到海上。首先，根据恒星星表精确、实时地计算出恒星位置。然后，通过坐标转换算法将其位置值转化到测量系下，运用船摇自稳定算法保证经纬仪的正常跟踪并记录数据。最后,根据事后解算算法分析记录数据，分离设备单项差并计算系统误差。实验结果表明，海上星校单项差的标定与坞内通过方位标标定结果非常接近，照准差、水平差、垂直差的偏差分别为0.015″、0.22″和0.014″，系统误差的标定与坞内结果具有很好的一致性，完全能够满足经纬仪海上标校的要求。

In order to meet the requirements of offshore calibration for theodolites and to reduce calibration costs, this paper presents a calibration method of shipborne theodolites. Using this method, almost all the work can be carried out at sea. At first, based on FK5 ephemeris, the apparent position of a star can be calculated in real-time. After the coordinate transition, bootstrap values in the measurement system are ready. The algorithm of ship movement is used to keep the stablization of tracking at sea. At the same time, real-time data are acquired and recorded, and the axis errors and system errors of the theodolite can be calculated based on several algorithms. Experimental results indicate that the precisions of the calibration in dry-dock and the star calibration are very close. The tolerances of visual axis error, horizontal axis error and the vertical axis error are 0.015″, 0.22″ and 0.014″, respectively. The star calibration agrees with the former results very well in system errors after calculations. It can satisfy the requirements of offshore calibrating of a ship-based theodolite.