At Delft University of Technology (DUT) a software suite has been developed for Continuously Operating GPS/GLONASS Reference Stations. The most important features of this software suite are a real-time GPS receiver interface, real-time integrity monitoring and communication with a computing centre. The sample rate of the receiver and the transmission rate to the computing centre can be selected independently, and the data are sent in discrete batches of several minutes up to 24 hours, or continuously. The data are stored on the local computer disk with the receiver's sample rate. The real-time quality control and integrity monitoring is based on a single channel approach. It uses a Kalman filter based Detection, Identification and Adaptation (DIA)-procedure. Presently, the AOA Turbo Rogue, JPS Legacy, Trimble 4000SSE/SSI and Trimble 4700 receivers are supported. The software also includes an interface for meteorological sensors. The software has been used since 1997 for the Dutch Permanent GPS Network and since 1999 for DUT's IGEX GPS/GLONASS reference station.

The principal observational characteristics of the Hipparcos Catalogue, and a summary of its main astrometric and photometric properties, are presented. Median astrometric standard errors (in position, parallax, and annual proper motion) are in the range 0.7-0.9 milliarcsec (mas) for stars brighter than 9 mag at the catalogue epoch (J1991.25). The catalogue is a materialisation of the ICRS reference system, coinciding with its principal axes at the level of ±0.6 mas, and with proper motions consistent with an inertial system at the level of ±0.25 mas/yr. The 118218 constituent stars provide a mean sky density of ∼ 3 stars deg^-2. The catalogue is available in printed and machine-readable forms.