The collocation and combination of different types of space Techniques is the basic concept of the Key Stone Project. In the SLR system, as a new calibration technique, ground targets (two bench marks and three pillars) are used to determine the system delay. Therefore, a local tie between the reference points of VLBI, SLR and GPS systems, as well as these ground targets would be of much importance.

We have done the ground survey for the local tie, in which a 3D triangulation and trilateration network observation method with a precise Total-Station is accepted. Higher accuracy leveling is also used to strengthen the height component of the network. Satisfying results are obtained with the 3D coordinates of both reference points of VLBI and SLR systems, as well as other reference marks, being determined within 1.5 mm (S.D.) on a local frame.

In this presentation, firstly we would like to give a brief introduction about the instruments we used, and the observation networks.�@Then, a detailed description will be given to how we determined the reference points of VLBI and SLR. The reference point of VLBI is the intersection point of axes. There is actually no real mark for it, so we tried to determine it in two ways, one directly and the other indirectly. The ground survey has been carried out three times, so finally, some results of the repeated observations will be discussed too.