Geometry

The geometric delay is computed in the following way:

$$\tau_g = \frac{{\bf b_{\cdot} s}}{c}$$

$$= \frac{1}{c}\left(X_{ij}\cos h\cos\delta - Y_{ij}\sin h\cos \delta +Z_{ij}\sin \delta\right)$$ (38)

This geometric delay is computed in real-time and applied in the correlator and on the LO for fringe tracking. However, it may be the case (and is quite usual) that after the observation, a better baseline model was determined. Another more unusual case would be new coordinates were determined for an observed source or that the time reference used at the observatory was offset w.r.t. UT1 time. All these can be corrected after the observations and the phases recomputed with commands MODIFY ANTENNA, MODIFY BASELINE, MODIFY POSITION or MODIFY TIME. In all cases, equation 39 is used with the updated parameters provided by the user.