Where or how can I find the approximate horizontal difference between wgs84 and nad83 in South Texas. I am trying to explain the difference to a crew that is working down there but I don't know just how much difference that is.
I know (or think I know) that it is about 3.35 feet here in East Texas.
This is a crew running waas corrected machine control on mulching machines.
*James
> Where or how can I find the approximate horizontal difference between wgs84 and nad83 in South Texas. I am trying to explain the difference to a crew that is working down there but I don't know just how much difference that is.
>
> I know (or think I know) that it is about 3.35 feet here in East Texas.
>
> This is a crew running waas corrected machine control on mulching machines.
>
> *James
Maybe demonstrate the difference by running a couple of points through corpscon?
My version of Corpscon doesn't list wgs84 but it may be an old version.
NAD 27
NAD 83(86)
HPGN/HARN
I tried finding an online conversion but didn't have much luck.
I also tried finding a later version of Corpscon.
James
Thanks Bill, There is not much that program won't convert.
1.078 meters
James
Now You'll Have To Explain Meters To The Crew
😛 😀
[sarcasm]Paul in PA[/sarcasm]
Now You'll Have To Explain Meters To The Crew
Yea, I'd better wait till Tuesday. That would be too much information to process on a Monday.
James
Howdy,
First of all, it is a little more complicated than merely comparing NAD83 to WGS84. At the time both systems were implemented they could be considered equivalent. NAD83(1986) pre-HARN, pre-GPS was computationally on the surface of the earth equivalent. Then matters got more complicated with new versions of NAD83 and the decision by those responsible for WGS84 to make it compatible with ITRF. Periodically WGS84 is defined to insure consistency with ITRF. WGS84 coordinates like ITRF and NAD83 have date tags. In the case of WGS84, when a redefinition takes place the new version is given the GPSweek number associated with the recomputation.
All that said, how do non-DOD users encounter WGS84? If you use broadcast orbits you do. Some software still tells you that NAD83 is equivalent to WGS 84. Unless you work for the military and they provide you WGS84 coordinates you are not using them even though you use broadcast orbits (unless you do autonomous positioning) because if you use NAD83 base station coordinates the result will be NAD83. There is an accuracy loss mixing NAD83 base station coordinates with WGS84 orbits but for most users it would not be significant.
All that said, given the fact that the current implementations of both ITRF and WGS are equivalent at the 5 cm level you can tell the difference at a point by submitting data to OPUS or OPUS-RS and comparing the NAD83 and ITRF 08 coordinates directly.
Doing accurate, high precision work does require knowledge of these datum issues.
I imagine NGS' Dave Doyle will be posting a reply. Hopefully, I have not mangled things too much.
See http://earth-info.nga.mil/GandG/sathtml/gpsdoc2012_02a.html for details about the latest implementation GPS week 1674!!!
Aloha,
DMM
Honolulu, Hawaii
To my knowledge, there is now way to check it. The NAD83 is essentially WGS84, but I was told it's about 2 meters.
Unless you could tie into DOD monuments, hmmmmmm. 🙂
Thanks GeeOdd,
I explained it as WGS84 is from the top down and NAD83 is from the ground up. But I like your explanation better.
Comparing NAD83 to ITRF from OPUS results is how I came up with the 3.35 difference here in East Texas but I don't want to drive all the way to South Texas just to do the same.
The HTDP program Bill posted worked pretty slick.
James
The U.S. Defense Department has been migrating WGS 84 to be closer and closer to ITRF. The relationships are defined in the NGA (National Geospatial-Intelligence Agency) manual TR8350.2 "WGS 84 Its Definition and Relationship to Local Geodetic Systems" you can find this specific info in section 2.2.1 (pg 2-5) as well as in the addendum posted on the web site. It's important to note that just as there have been several different realizations of NAD 83 (e.g. NAD 83 (1986), NAD 83 (CORS96), NAD 83 (2007) etc), there have been five realizations of WGS 84 - WGS 84 (TRANSIT), WGS 84 (G730), WGS 84 (G873), WGS 84 (G1150) and the most current WGS 84 (G1674). To determine the best relationship to NAD 83 the specific realization of each reference frame needs to be defined. The most current realization is so new that they don't have any info posted at this time, but essentially WGS 84 (G1674) = ITRF08.
If you get involved in cm-level accuracy it is important to note that NGA does not seem to define an epoch for these realization. For example NAD 83 (2001) is defined at epoch 2010.0, NGA does not provide a corresponding epoch for the various WGS 84s so there's always a bit a "wiggle" between coordinates.
"wiggle" - interesting...
Thanks Dave!!:good:
