The change to our base station positions was minimal. The amount of the change varies at each base station, but the network-wide average shift is approximately 2 cm (0.06’ or 3/4”) horizontally and 5 mm (0.02’ or 3/16”) vertically (ellipsoid height). It is important to note, that users will not need to do anything, if they can live with approximately 3/4" horizontal and 3/16" vertical shifts. Otherwise, transformation(s) from NAD83(CORS96) to NAD83(2011) will be needed to used the IaRTN on previous projects.
Secondly, a new geoid (Geoid12A) has been released by the National Geodetic Survey to replace the old geoid (Geoid09). Starting immediately, it is highly recommended that all IaRTN users use Geoid12A, if working with elevations/orthometric heights. The user (not the IaRTN) determines which geoid is used.
Contact me if you have any questions.
Statewide RTN Coordinator
Iowa Department of Transportation