Published online by Cambridge University Press: 03 August 2017
The modern space techniques have achieved such an unprecedented accuracy and precision in position measurements that there is required a rethinking and reformulation of reference frames, both in their concepts and in their realizations. Various reference frames are a natural consequence of the different observational techniques and data types. Not only are the determination and the necessity of these various frames stressed, but also their evolving nature is recognized. The current status of frame ties is highlighted, and the need for improved ties is motivated. We conclude with our concerns and recommendations.