国际地球参考框架ITRF是全球最高精度的参考框架。其中并址站归心基线作为联系ITRF中各观测技术的主要约束条件，已成为实现ITRF精度提高的主要因素。现有在站心坐标系和独立坐标系中分步解算和构建坐标转换方法难以满足ITRF对归心基线精度的需求。本项目基于多类观测数据，在ITRF中建立多类观测数据进行整体处理的严密平差模型，以消除多类观测数据之间坐标基准不统一、系统性误差、精度差异等影响；提出将归心基线的ITRF坐标作为未知参数，构建归心基线、两轴偏差等未知参数之间的多种约束条件，实现归心基线在ITRF中的整体解算，优化分步解算方法和坐标转换方法；研究GNSS数据处理策略和多种约束条件对归心基线的影响程度，揭示主要因素（新的归心基线、并址站分布、归心基线精度和特定的归心基线）对ITRF实现的影响规律和特征。可为实现更高精度的归心基线和ITRF提供理论基础和科学依据。

The International Earth Reference Framework (ITRF) is the highest accuracy reference frame in the world. Local tie vector, a major constraint of the observation technology in the ITRF, has become the main factor for improving the accuracy of ITRF. Methods of step by step solution and coordinate transformation in the topocentric or the independent coordinate system are difficult to meet ITRF requirement for accuracy of the local tie vector. Based on different types of measurements, this project establishes a rigorous adjustment model for different types of measurements in ITRF to eliminate the inconsistency of coordinate reference, systematic error and accuracy difference among different types of measurements; The ITRF coordinates of the local tie vector are taken as unknown parameters, and the constraints between the local tie vector, the two-axis deviation and other unknown parameters are constructed, and the whole solution of the local tie vector in ITRF is realized, and the methods of step-by-step solution and coordinate transformation solution are optimized. The project studies the impact of GNSS data processing strategies and various constraints on the local tie vectors, reveals the main factors (new local tie vectors, the distribution of global co-locations sites, the accuracy of the local tie vector, specific local tie vectors) on the impacts and characteristics of ITRF. It provides a theoretical basis and scientific basis for achieving a more accurate local tie vector and ITRF.