The PID is AC7974. Here is a copy-paste of the first page of the NGS data sheet:
DATASHEETS The NGS Data Sheet
See file dsdata.txt for more information about the datasheet.
PROGRAM = datasheet95, VERSION = 7.89.4
1 National Geodetic Survey, Retrieval Date = SEPTEMBER 14, 2012
AC7974 ***********************************************************************
AC7974 CBN - This is a Cooperative Base Network Control Station.
AC7974 DESIGNATION - 212 286.65
AC7974 PID - AC7974
AC7974 STATE/COUNTY- SD/HAND
AC7974 COUNTRY - US
AC7974 USGS QUAD - MIRANDA (1966)
AC7974
AC7974 *CURRENT SURVEY CONTROL
AC7974 ______________________________________________________________________
AC7974* NAD 83(2011) POSITION- 44 53 48.68063(N) 098 55 02.29088(W) ADJUSTED
AC7974* NAD 83(2011) ELLIP HT- 410.850 (meters) (06/27/12) ADJUSTED
AC7974* NAD 83(2011) EPOCH - 2010.00
AC7974* NAVD 88 ORTHO HEIGHT - 434.946 (meters) 1426.99 (feet) ADJUSTED
AC7974 ______________________________________________________________________
AC7974 NAD 83(2011) X - -701,566.421 (meters) COMP
AC7974 NAD 83(2011) Y - -4,471,274.759 (meters) COMP
AC7974 NAD 83(2011) Z - 4,479,525.896 (meters) COMP
AC7974 LAPLACE CORR - -3.09 (seconds) DEFLEC09
AC7974 GEOID HEIGHT - -24.09 (meters) GEOID12A
AC7974 DYNAMIC HEIGHT - 434.889 (meters) 1426.80 (feet) COMP
AC7974 MODELED GRAVITY - 980,473.9 (mgal) NAVD 88
AC7974
AC7974 VERT ORDER - FIRST CLASS II
AC7974
AC7974 FGDC Geospatial Positioning Accuracy Standards (95% confidence, cm)
AC7974 Type Horiz Ellip Dist(km)
AC7974 -------------------------------------------------------------------
AC7974 NETWORK 1.10 3.18
AC7974 -------------------------------------------------------------------
AC7974 MEDIAN LOCAL ACCURACY AND DIST (018 points) 1.33 3.94 49.60
AC7974 -------------------------------------------------------------------
AC7974 NOTE: Click here for information on individual local accuracy
AC7974 values and other accuracy information.
AC7974
AC7974
AC7974.The horizontal coordinates were established by GPS observations
AC7974.and adjusted by the National Geodetic Survey in June 2012.
AC7974
AC7974.NAD 83(2011) refers to NAD 83 coordinates where the reference
AC7974.frame has been affixed to the stable North American tectonic plate. See
AC7974.NA2011 for more information.
AC7974
AC7974.The horizontal coordinates are valid at the epoch date displayed above
AC7974.which is a decimal equivalence of Year/Month/Day.
AC7974
AC7974.The orthometric height was determined by differential leveling and
AC7974.adjusted by the NATIONAL GEODETIC SURVEY
AC7974.in July 1998.
AC7974
AC7974.The X, Y, and Z were computed from the position and the ellipsoidal ht.
AC7974
AC7974.The Laplace correction was computed from DEFLEC09 derived deflections.
AC7974
AC7974.The ellipsoidal height was determined by GPS observations
AC7974.and is referenced to NAD 83.
That's a HARN by golly.
I sympathize with your situation. Getting your supervisor's to understand why their expectations are somewhat unrealistic is quite a challange.
The goal of my project is to survey some wells to within 2 cm vertical accuracy.
Please review the stated accuracy of this HARN. The Height accuracy is above 3cm. Your expectation is not met before you begin.
That's not the reason you are off by huge amounts however. I don't work with Trimble software anymore so I can't help you wiht that. That Lawton guy had some good pointers.
You might want to inform your supervisors that the local and network accuracy of the marks you are being asked to use are higher than the goal to start with. I don't think they are going to want to spend the kind of $$ it takes to get the goal. You are probably looking at a digital level loop network for each well. Lots of work involved there.
EDIT: I suppose I should tell you what is involved. First you have to run level loops to verify the first or second order accuracy of marks surrounding the well. Those marks may be subject to surface motion and may not be as accurate as stated to start with. So you have to determine which marks are holding their published heights. Then you have to level from those marks to the well and evealuate the accuracy of the leveling work. Depending on the distance from the mark to the well your 2 cm expectation may be exceeding even first order work.
Chances are they are going to tell you do the best you can. So to cover your hiney I would review the FGDC methods for stating accuracy and follow them and publish the true accuracy error. Engineers as a rule don't want to hear that there is accuracy error associated with a height but sometimes the truth hurts.
Jim,
> Project Settings|Baseline Processing|General|Antenna model. You'll be able to >select NGS Absolute from the drop-down menu. (P.S. I haven't found this using the >ribbon interface yet. The above pertains to the classic interface.)
I've found this and experimented with it, but TBC states that some of my occupations aren't NGS absolute. My question is how do I know if my occupations are using NGS absolute calibrations? Is that something I can change in my field data collector (I'm using Trimble Digital Fieldbook)? Is there an antenna calibration file I can download and import into TBC to use NGS absolute calibrations for processing? That is where I'm confused.
> 1. Set up the TBC project (units, location, geoid model, processing style, etc.) >Specify a processing style that uses a fixed integer solution, NGS absolute antenna >models, precise ephemerides, and a 15° elevation mask. (You may want to change the >mask later, but 15° is a good place to start.)
This I have mostly figured out and done. I have my coordinate system set up for UTM Zone 14N, NAD83 (2011), and GEOID12A, which are the same as what is indicated was used for defining the HARNs on their data sheets. I also have set my elevation mask to 15 deg in both TBC and in my field collector. Max PDOP was set at 6.0. I have downloaded the rapid ephemerides and imported them into TBC and also set it to use fixed solutions.
> 2. Send at least one data file from each station to OPUS-S or OPUS-RS.
I've tried this. I submitted the .t02 files, but OPUS returned that it could not convert them to RINEX. After a while, I found an application to convert them to RINEX, Trimble's Convert to RINEX utility, but even then I could not get them submitted. It would not accept the .12N file, and it said the .12O file could not be processed because it was either too noisy or a kinematic observation (it was fast static). I tried zipping the two files using PKZIP since OPUS said it would accept that, but it still said it could not read the .12N file. I've e-mailed OPUS for help on this, but haven't heard back, so if you can explain what I'm doing wrong, that would be great.
> The NGS-58/59 guidelines specify 45 minutes of data for no more than 10 km lines, >and I've found 1 hour to be more practical at that distance. 10 miles is about 16 >km; 14 miles is about 22 km, so you're outside the guidelines right off the bat. >I'd go at least 2 hours for 16 km, and 3 hours for 22 km (about 14 miles). You may >be able to get by with less, but since there's no widely-accepted specification to >point to, I advise erring on the side of caution.
This is good advice, thanks. I was already pretty sure I needed to do more and longer occupations to get the accuracy desired. I'm also aware of separating observations by 3 hours to get different constellations. I will definitely check out those guidelines. Most of my decisions on occupation times was based on questions to the support people at the dealer who sold us the equipment. I may not have been clear enough on the scope of my project for them to provide me with good advice. And to clarify some concerns others have expressed, this data will be primarily for internal use. The purpose is to have highly accurate elevations of well heads so that measurements of water depth and the locations of the geologic features where the water is found are also highly accurate. My supervisors are more familiar with something like the Trimble GeoExplorer3 that we have. They purchased this equipment with the notion that it could be used to get those cm-accurate elevations but not realizing it was much more complicated. However, they know I'm not a surveyor and would not use poor quality data. This is more or less an experiment to see if we can actually make use of this equipment for the purposes we hoped to use it for. The trick is this project is about four hours from my home base and already required two weeks of out-of-town travel. Cost might eventually factor into whether we do this ourselves or pay someone else to do it.
Minor Thread Hijack
Jim - So far, the only way I can find to access the Project Settings in Ribbon View is to right-click on the project name in the Project Explorer.
That is a bench mark that was occupied to create a HARN point.
You found the stainless steel ball for the point?
There are no reference monuments for this one so that can't be your problem.
As others have stated the accuracy of 2cm or +-.07' is very tight.
The first thing is to determine 2cms to what?
To local elevation control which this HARN point is part of?
NAVD88 or NGVD29?
To GPS heights converted to elevations with a Geoid model?
Which model?
My assumption is that they want local elevation (probably NAVD88), which means tying into bench marks that are "close" to the wells and adjusting to them. That can develop into quite a project.
What they probably actually need is +-.5' or so for the elevations.
These standards get pretty silly with respect to well locations. I've had a number of projects where they wrote the specs to require 0.01' accuracy for elevations on water wells. Of course it was not possible without a really tight leveling campaign and they never want to spend that much money, I usually talk them into a 1/4 or 1/2 foot spec. to some defined elevation system.
> We have a Trimble setup of three R3 receivers with A3 antennas
I overlooked this in your original post. The R3 -- I had to look it up -- is a single-frequency receiver. This means that there is no NGS calibration for the A3 antenna, and that OPUS can't make use of your data. It also means that you're operating outside the 10 km range for L1-only equipment specified in NGS-58. In my opinion, your equipment isn't capable of meeting the project goal under the circumstances.
You could try to patch things up by observing infill control to bring all the vectors under 10 km, but you'd still be fighting the limitations inherent to L1-only receivers. You'd have to rely on the Trimble antenna model, and forgo any OPUS assistance.
I believe your supervisor handed you a job that was doomed from the start. Through no fault of your own, the absence of in-house expertise necessary to understand the requirements imposed by the goal have led you down a path to nowhere. It's time for your supervisor to take another look at what he/she really needs and then take an informed look at how to get there.
> > We have a Trimble setup of three R3 receivers with A3 antennas
>
> I overlooked this in your original post. The R3 -- I had to look it up -- is a single-frequency receiver. This means that there is no NGS calibration for the A3 antenna, and that OPUS can't make use of your data. It also means that you're operating outside the 10 km range for L1-only equipment specified in NGS-58. In my opinion, your equipment isn't capable of meeting the project goal under the circumstances.
>
> You could try to patch things up by observing infill control to bring all the vectors under 10 km, but you'd still be fighting the limitations inherent to L1-only receivers. You'd have to rely on the Trimble antenna model, and forgo any OPUS assistance.
>
> I believe your supervisor handed you a job that was doomed from the start. Through no fault of your own, the absence of in-house expertise necessary to understand the requirements imposed by the goal have led you down a path to nowhere. It's time for your supervisor to take another look at what he/she really needs and then take an informed look at how to get there.
Thanks, Jim. I knew that it was only an L1 antenna but I did not know that OPUS only accepts dual-frequency data. That also explains why there was no antenna calibration. I figured that a dual-frequency receiver would be better for this type of project, but this is what we have. It does say that it had carrier-phase, which I know is not the same as dual-frequency, but I was hoping it would help a little bit. I don't blame my supervisors for handing me the project. I think they were as ignorant of the complexities of this type of GPS surveying as I was and were probably just going with what they were told this equipment was capable of when the dealer sold it to them. I'm certain we'll be able to figure something out, either accepting accuracy within the limitations of our equipment or going with something else altogether.
Oops. Ignore my part about OPUS, since you have single freq's. But it's still okay to download CORS and use them to process against your data. Just be careful in the distance since the single frequency solution cannot do an iono free solution.
I've used singles well over the stated limits but that is after years of looking at data and having a really good understanding of why I might have a float and if it still can be a valid solution. They often can but it does require experience.
He can try CORS but here is a map of the area:
You might get a solution but there isn't much out there.
It almost looks like Cors has an allergy to South Dakota
I did download CORS data from the nearest station, CLK5, but it's about 75 km from the HARN closest to it. There is another continuously recording station operated by the SD DOT in Pierre which I have access to. It is not a CORS station, though, and it's still about 80 km from the nearest HARN.
I notice that dliviskie does not claim to be a surveyor, and surveyors usually use dual rather than single frequency receivers. I also notice the original poster uses a mix of feet and metric units in the original post. So I wonder if the original poster has rigorously tested his/her process for distinguishing between international feet and survey feet. (Or perhaps the OP is only working in metric, and only stated the horizontal error in feet for purposes of the forum post?)
Wow! Talk about nearly 0.0% coverage. That pretty much rules out even self post-processing with single frequency units. Dang.
You are correct in your perception that I am not a surveyor. I'm just a technician trying to do the best I can. I don't believe anyone in our agency is a professional surveyor as it's not really part of our mandate. Some people in my office do have experience, but not with GPS surveying. However, we do sometimes want/need very accurate locations, and we paid for this equipment so we're trying to get some use out of it. But as I said before, I don't think it was understood well what the limitations were for getting the kind of accuracy we were told it was capable of when the it was purchased, or of the technical knowledge and background needed to really use it effectively. I'm the guinea pig, and whatever I learn I can pass on to others, or at least determine that more professional training is needed. As for mixing units, sorry if that was confusing. I have been working in meters and prefer to use that, but I wasn't sure what units those on this forum would be more familiar with, so I used feet for the original posting.
>by linebender @, Wednesday, October 17, 2012, 14:31 (22 hours, 38 minutes ago) @ dliviskie
Skie
The chance that the datasheets are off as much as you indicate are about a thousand times less than the chance there is something wrong with your survey and/or computation process. I've always found FBN or CBN accuracy to be as stated on the datasheet.
I guess I should play the lottery because it turns out the HARN data sheet IS incorrect. I just got an e-mail from one of the state surveyors. The original monument was destroyed a few years ago during reconstruction of the highway. They re-monumented it in 2008 in a slightly different location. Inputting those coordinates and now I am within 1.5 meters horizontally and vertically. Still not the accuracy that I wanted, but at least it makes sense that my data is almost on the point and not 75 meters off. I'd like to say thanks to everyone who posted offering me advice. It's been informative and helpful in deciding what I need to do to make this project work. I'm still open to hearing any more suggestions you have to improve my results on this project or my surveying skills in general, as rudimentary as they may be.
Nasa has an online positioning service (PPP) http://apps.gdgps.net/ and can be helpful in looking for blunders when there are few CORs around. Not as good as OPUS and you need to do long observations (plus they have a 5mb upload limit per session), but in SD and a lot of Canda these are a good last resort. Canada DNR has an online PPP service but then you would have to deal with a different reference framework.
I'd like to add one more thing. Your units, while only single frequency are capable of CM level results, if used within their limitations. This is generally spec'ed in the sheet and for singles deal with distance between units.
To minimize error (or maximized distance) you can run the units longer and at night after the sun has gone down. We proved quite a bit years ago during what was called our Redneck Science Experiments with L1 only units. But we never achieved the results using the standard occupations that the manufactures suggested. It required following sites like space weather and watching the kp index. Then longer occupations and for certainly sites that were 100% open with no obstructions.
And I'll mention, but I'm sure you know, but I've seen someone ask before. You cannot used a L1/L2 CORS and L1 data and expect to get the same results as L1/L2 and L1/L2. Lowest common denominator rules apply.
Best of luck.
Thanks Deral. I do realize I can get cm-level accuracy, but it was not clear to me (or my superiors when they purchased the equipment) the limitations within which it was possible. Now that it is, I am planning to go back up in mid-November and will be doing longer occupations, multiple occupations, and even occupying at night if it's feasible, although the weather might become an issue by then. Obstructions on the HARN sites shouldn't be a problem- they're on highway ROW out in the open prairie. However, some of the wells have windbreaks of trees nearby, though maybe with the leaves off that will reduce the attenuation of the signal somewhat. I'm going to try to follow the NGS-58 guidelines as much as possible. Establishing the accuracy of the HARN points is the first step. Once we know we can get reliable and accurate data on them, then we can starting thinking about the wells, or possibly establishing secondary base stations using non-HARN benchmarks to shorten baselines and then do the wells. And no, I didn't know that an L1- only CORS solution would not be as good as an L1/L2 CORS solution, but that makes sense when I think about it. I appreciate all your help.
Yeah, can be pretty empty out here. In fact, if you combine the populations of OKC and Tulsa proper, not even including the surrounding metro areas, you have more people than the entire population of South Dakota.
Another example- the county I'm working is slightly larger than the state of Rhode Island but has less than 3,500 people.
I thought this was a joke.