Modern GNSS networks constantly output coordinates in dynamic, global reference frames like ITRF or modern WGS84 realizations. These coordinates physically 'move' over time due to crustal velocity.
Transformation Workflows
To tether a dynamic GNSS shot to a static local blueprint, data analysts execute a multi-step transformation: First, determine the exact epoch (time) the data was collected. Second, apply a velocity model (like the NGS HTDP model) to roll the coordinate back to the official standard epoch (e.g. 2010.0 for NAD83(2011)). Finally, execute the 14-parameter Helmert transformation to shift the underlying ellipsoid reference. This guarantees millimeter-level fidelity.