I am trying to help a friend post process some GPS data for a cell tower. He has three Locus units, which are L1 units only. He collected about 3 to 4 hours of data with all three units.
I am have created a VRS point, and then tried post processing against the VRS. I have only one fixed vector from the VRS point to one of the occupied points. The other two vectors did not fix. The vectors between the three vectors were fixed amongst themselves.
I do have a latitude and longitude from a previous survey that I can check against, and my post processed position is within 7.8 feet of the original published location, which was stated as having an accuracy of approximately 50 feet.
One question that I have is what is the difference bewteen the NAD83-86 Zones and the NAD83-CORS96 Zones?
I must have messed something up, because when I processed the points, and exported them, and compared the distances, my distances between my post-processin points was off by approximately 3 feet between the outermost points. My friend processed them, and was within hundreths. I am not sure exatly what was/is going on. It was pretty late when I was processing them, so it is probably a user error.
Thanks in advance for any help you can give me on this.
Jimmy
How far away are the CORS stations you're creating the VRS point from?
Mark,
Thanks for the reply.
The stations are:
60 miles
48 miles
48 miles
There are a few sites a little closer, but for some reason the data is not available for that date.
Thanks,
Jimmy
I don't really have a ready answer. I'm assuming the Locus Observations were blind and no control data was tied to in the network. If it was I'd use Ashtech Solutions, but from what you've described, probably not. The baseline lengths are long, but I've used similar in the past and checked within a couple of tenths to NGS monumentation.
This doesn't sound like it's your first rodeo, so I'm assuming you have all tor BD&E files, etc.
Paul in PA might have more to offer if he's monitoring this. I would make sure I was using the same geodetic datum for all my work, past and present. Datum differences can easily account for a three to four foot shift.
Jimmy, You've Got Mail
Reply to my email with the files.
Paul in PA
Howdy,
With respect to your question about the magnitude of the difference between NAD83(1986) and NAD83(CORS96), you can compute the difference using NADCON and the new GEOCON and GEOCON11 tools. The latter two programs are on the NGS beta site and linked from http://www.ngs.noaa.gov/web/news/Beta_Release_of_GEOCON_and_GEOCON11.shtml
The magnitude of the difference between NAD83(1986) coordinates and the subsequent HARN coordinates in Campbell County, TN is about 0.3 meters (~ 1 foot). The difference between the HARN, NAD83(1995) coordinates and NAD83(CORS96) would be on the order of a few centimeters.
Remember that the original NAD83, officially known as NAD83(1986) did NOT include GPS. The subsequent HARN surveys, observed state-by-state, refined coordinate values by virtue of the use of GPS. Later GPS surveys (and adjustments) further refined coordinates with smaller changes.
HTH,
DMM
I Have Excellent Results
I am using Ver 3.80.8 and have not yet gotten a code to unlock L1/L2 in this version.
Since I had not checked my options to download the IGS orbit it processed the VRS with the broadcast orbit. I have since manually gotten the rapid orbit and my reply was delayed since a recent Widoze update again removed 7-Zip from my computer. Windoze blocked my download of 7-Zip 4 times before I finally got it.
I will redo the VRS from scratch with the precise orbit settings on another day and see if it affects the VRS position.
I selected ALBE, MSOX and MSST CORS.
My greatest vector residuals are 0.002m and my Locus position errors are 0.002m (ENandEllips).
I created a RINEX file for my VRS position and am awaiting results from OPUS as verification of my software position. I am resubmitting to OPUS as OPUS went and found my default Leica 502antenna and height of 2.146m instead of the NONE 0.00 I entered. It should now since I reset my profile.
North GNSS 55481.350m OPUS 55481.346m
East GNSS 313327.174m OPUS 31333327.159m
NONE 0.00 results
North GNSS 55481.350m OPUS 55481.349m
East GNSS 313327.174m OPUS 31333327.160m
Ellips GNSS 91.906m OPUS 90.668m
The heights I will further investigate.
I see no problems, so ask questions on what may be the problem.
Paul in PA
I Have Excellent Results
Thanks for the replies guys.
I am in the field, and will reply in more detail later this evening.
I did watch some training videos yesterday while it was raining, and I feel pretty good about what I came up with.
After watching the videos, and reprocessing in WGS84, and then changing over to MS NAD83 East Zone, I was within 6.8 feet of the original published Lat/Long, which had a stated accuracy of +/-50'.