This is a reminder that the Iowa Real Time Network (IaRTN) will be switching from the current NAD83(CORS96) datum to NAD83(2011) datum. The network will go off line at 5:00 pm CST tomorrow, Friday, January 4, to update the reference station positions to NAD83(2011) and come back online by 7:00 am CST on Monday, January 7.
The change to our base station positions will be 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.
Make sure you have good control on all existing projects requiring transformations to NAD83(2011), if you plan to use the IaRTN on those projects beginning January 7.
Secondly, a new geoid (Geoid12A) has been released by the National Geodetic Survey to replace the old geoid (Geoid09).Starting January 7, 2013, 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