Okay, I have been using the local Topcon as well as the local INDOT RTK Network GPS (we call that RTN now, right?) for many years now.
I am used to getting NAVD 1988 elevations to match published benchmarks pretty well, say a couple tenths or better usually.
When I am checking into a NGVD 1929 benchmark around here I usually find my GPS (NAVD 88) elevation to be less than 1 foot lower-ish than the published NGVD 1929 elevation of the benchmark I am checking into.
Earlier this summer I had the firmware updated on the Hiper+ unit. I have verified the settings for the rover antenna height, it shows 6.562 feet.
However, on the last 2 jobs I have done this summer the GPS (88) elevation shots on existing published (29) benchmarks have been coming in about 3 feet HIGHER.
It is a little uncomfortable and strange. I don't understand what is happening. It seems like there is some other setting wrong somewhere. This happens in BOTH the TOPNEXT and the INDOT networks.
What is going on?
Thanks.
Almost sounds like an itrf datum vs a nad83 datum. There is a 4+ foot difference in Texas between the two vertically.
> Almost sounds like an itrf datum vs a nad83 datum. There is a 4+ foot difference in Texas between the two vertically.
Like maybe I should choose NAD83_NO_TRANS here instead of NAD83 ?
Yeah. I think you found it.
> Yeah. I think you found it.
Sweet. Thanks brother.
Yet ANOTHER opportunity for me to contribute to the tip jar. Of course it won't be any where close to the value I just received. But alas, it is the thought.
Thanks Shawn!
Sweet. Hope it works!
I ran into the same thing after installing the 80 IaRTN DOT LGS reference stations in Iowa. During the certification trials tying into the IADOT HARN stations, everybody's NTRIP RTK Rovers, accept the Topcons checked in "AOK", it took a couple of hours, and multiple calls to TPS Tech Support, before selecting the "NAD83 NO TRANS" setting. Software right??
-BbB B-)
It is unfortunate nomenclature that Topcon selected, BUT I have to give them credit for recognizing that NAD83 and WGS84 aren't the same, that is what they are trying to do and few other manufacturer's have made that distinction, at least on the field software side.
If you already are receiving NAD83 in the broadcast, then you select the no trans, if you want NAD83 and the reference is in ITRF / WGS84, then you select NAD83 to make the transformation, the unfortunate part is unless you set your base to broadcast ITRF /WGS84, then selecting NAD83 will transform an already transformed value creating havoc!
I use GravNav/Inertial Explorer from Waypoint Consulting as one of my post processing packages, they also include transformations from ITRF to NAD83, BUT they actually name the transformation such as ITRF08->NAD83(2011) so it is pretty clear what the software wants to do.
I suspect the unfortunate naming came about in some translation to English someplace.
SHG
