tsc_TiltedEcefObservation

This a subclass of tsc_TiltedGnssObservation, and contains a tsc_Ecef coordinate.  This type of observation is used to store measurements taken by a explicit tilted pole measurement in a position-storing GNSS survey.

The ECEF coordinate should be in terms of the raw ECEF supplied by the instrument (i.e. in the case of mixed RTK-RTX surveys use the native ECEF).

Such an observation can only be appended to the database while a current survey is running.