We do all our surveying in state plane coordinates and tie it to OPUS observations which are NAD83(2011). This data get used by GIS folks and I am wondering what is the correct datum for them to use when loading the data.
They have been using just plain old NAD83 which I assume is the 1986 and it gets them close enough certainly within the accuracy limits of their GPS. Looking at the GIS software the datum choices are NAD83 and the various NAD83 state harn/hpgn's. Would the harn be a better match to NAD83(2011)?
I know in most areas we work the difference between NAD83(86) and harn is less than a foot which is of no consequence for the purposes of this data but I was just wondering what would be the more correct choice.
There may be exceptions, but I'd think the later the datum realization you tell the software to use, the closer it would be to NAD3(2011). HARN would be closer in most cases to 2011 than was NAD83(86). You could pull up some NGS data sheets for HARN or better stations in the area of interest and look at the current versus superseded values to get a better idea.
What reference frame(s) the base layer data they are using are in the GIS?
How accurate does the GIS need to be for the intended purpose?
Regardless of which reference frame you enter the positions with, the most important thing to do is to document with detailed metadata. Add the OPUS solution as an xml or txt file to the documentation.
Thanks guys.
The GIS uses data of various sources and reference frames. Basically any time anything is loaded into it a window pops up asking about datum of the data. They load aerial imagery, abstract shape files, digital elevation models, utility location shape files, etc.
I put all the OPUS info into the headers of the CSV files I provide but I was asked by a client what to choose as my data said NAD83(2011) and his only choices were the plain NAD83 and the NAD83 HPGN.
They take this data and load it into WASS GIS grade GPS units and navigate to the points I surveyed and the accuracy of those units doesn't expose any reference frame errors. I think last time I checked in our area it was like an 8" difference between 86 and HPGN. Basically they use GPS to navigate to my survey marks and if they get close enough to find my mark they are happy.
I still would like to be able to have them at least get the data into their database in the most accurate means possible even though it probably doesn't matter in a practical sense. It just kind of bugs me I guess. The only reason I use RTK for what I do is the elevations of my surveyed points are pretty critical but sub meter on the X,Y's is good enough.