NAD 83 v. NAD 83 No Trans ?

Definitely poor nomenclature. Might be clearer to call it NAD83 from ITRF or something similar.

I'm very interested to see the explanation of this...

The whole WGS84/ITRF/IGS/NAD83 thing has been a Charlie-Foxtrot almost since Day 1.

Too much software, written by too many folks, who in too many cases, don't really know the difference. GIGO in spades.

What's going on behind the curtain???

In too many cases, it's pretty hard to find out for SURE!

:-@

Hi Paul,

Does the software have a coordinate system manager where you can display the transformation parameters? Most software assume WGS84 and NAD83 are identical. For example one software I use has this (which is obviously wrong):

NAD83-CSRS
DX to WGS84 = 0 m
DY to WGS84 = 0 m
DZ to WGS84 = 0 m
RX to WGS84 = 0 "
RY to WGS84 = 0 "
RZ to WGS84 = 0 "
Scale Factor = 0 ppm

This is very common. I can think of two or three other software's that assume the same. If you are doing RTK this is ok, since your result will be in the coordinate system of your base station coordinates, but for single point positioning they will differ by over a meter in most cases.

Shelby H. Griggs, PLS explained it quite well in another post:
"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!"

Bottom line, with Topcon gear use NAD83_NO-TRANS when working on an RTN or VRS, so long as the you are already receiving NAD83 in the broadcast. I would assume most if not all networks are broadcasting in NAD83, therefore no translation is required. Thus the name NAD83_no-trans.

Howdy,
u
Please note that the tranformation parameters you show are between the US and Canadian versions of NAD 83. CSRS stands for Canadian Spatial Reference System. The US NGS and GSD Canada have or had different transformation parameters between NAD 83 and ITRF. If you use their excellent PPP tools you should be careful about the compatibility of the transformed NAD 83 coordinates with US NSRS points.

The original versions of both WGS84 and NAD83 were equivalent on the surface of the earth. They were developed separately. Those tranforming between XYZ and Lat, Lon, Ellipsoid heights see a small difference in flattening.

NGS refers to the original version of NAD 83 as NAD 83(1986). Subsequent versions have different designations.

WGS 84 has undergone revisions mostly in attempts to keep it consistent with ITRF implementations. They note the version of WGS84 by including the GPS week when it was implemented. As most users do not have access to WGS coordinates except perhaps as NGA precise ephemerides the issue I don't see a problem with considering the most recent version of WGS84 as equivalent ith the most recent version of ITRF.

As for the original issue, the software should be clear and "NAD83 no trans" is not. Early packages did set NAD83 as equal to WGS 84. This is no longer the case. As indicated in other threads, there are significant differences resulting from confusing NAD versions and the differences between NAD 83 and ITRF (and WGS 84).

Cheers,

DMM

Hi GeeOddMike,

There are still many softwares (unfortunately most GIS softwares) that do assume WGS84 = every version of NAD83 (regardless of Canadian or US), knowing full well that this is incorrect. The transformation parameters that I showed early was an example of a software released in 2013 that does exactly this.

From the Magnet help file

http://caronpositioning.com/index.cfm?ref=30174&ref2=67

We actually found out the hard way with Caron East that they use the ITRF and call it WGS84.