What is actually a difference in TBC between using Site calibration, Coordinates transformation, Local site settings??
Aren't they take you to the same point I mean get rid off scale factor???
Which one and when should be used in practice??
A Site Calibration aligns the local latitudes and longitudes to a local coordinate system by creating a transformation between points common to both systems. It is most commonly used when an existing local coordinate system such as a plant grid must be used with GPS. In order to perform a site calibration (and get good results) it's necessary to have at least four or five points that are known in the local grid and that bound the area of interest.
A Coordinate Transformation is typically a classical Helmert or Moledensky transformation between two datums, such as would be used to transform between NAD83 and NAD27.
Local site settings can be used for a relatively small area to mitigate scale factor. The big difference between using local site settings and a site calibration is that a site calibration is aligning to several known points in an existing grid system, whereas local site settings are more typically creating a new local grid system. With local site settings you specify a scale factor and origin and everything is scaled accordingly. Typically the coordinates are also truncated in order to differentiate them from State Plane or UTM or whatever. I've used this method to re-create a plant grid when there was little or no extant control available.
