I use RTK on a regular basis for work but really the tolerances for what I do are submeter so I don't know a lot about the ultra precise stuff. Normally I collect a couple days of opus data while we are surveying and consider it good.
At my house I have permantly mounted a 5/8" stud on a heavy duty pipe set in 4' of concrete. I intend to use this to mount my base on for all types of projects on my acreage. Nothing involving legal boundaries or anything like that but I want to make sure I have really good coordinates for where it is so that my database I build of things around my place is correct. In all likelihood it really probably doesn't matter much but I want it right.
My question is how much OPUS data do I need to get the best results? I and sure more is better and 24 hours a day for a year would be ideal but practically speaking how much do I need to collect for a very good position? I plan to use the coordinates of this point for many years to come and may survey thousands of points off of it.
Is it better to do 24 hour sessions or a bunch of shorter ones?
A couple of hours for a couple of sessions for a couple of days for horizontal.
To establish an elevation add a few hours to the aforementioned.
This is assuming you have decent proximity to the cors network.
I'm sort of old school now, so if some of the cors are greater than 50 km, I would extend the sessions a little longer and process independently besides the OPUS solution.
I guess I became a belt and suspenders type of person too.
These marathon sessions that you are describing are of no consequence.
Trust the math!
Ok - thanks. I have already collected three five hour sessions because that is how long my internal batteries last and I didn't drag out the deep cycle.
I was thinking I might need a lot more but wasn't sure. Maybe it was sloppy work setting up the tripod as I didn't do it myself every day but on a recent job where we worked for ten days we collected opus data every day for at least 8 hours a day and when I processed them all there was about a 3" spread in the ten different solutions.
You can also review research. When using OPUS you need to verify he quality of the solutions using the guidance linked from the site.
One recommended site is:
The first link is to a compilation of articles from various sources (some linked to pay sites). The second addresses the specific issue of how length of sessions impact results.
http://geodesy.noaa.gov/CORS/Articles/
http://www.ngs.noaa.gov/CORS/Articles/Time_v_Distance.pdf
HTH,
DMM
Drilldo, post: 381179, member: 8604 wrote: My question is how much OPUS data do I need to get the best results? I and sure more is better and 24 hours a day for a year would be ideal but practically speaking how much do I need to collect for a very good position? I plan to use the coordinates of this point for many years to come and may survey thousands of points off of it.
Is it better to do 24 hour sessions or a bunch of shorter ones?
I'm assuming that you are somewhere within a couple of hundred miles of CORS sites. If you are much, much closer, this advice will be conservative. As long as your antenna is in a wide open area and the local weather is without thunderstorms, in my experience, six-hour sessions on three different days should give a result that is essentially the final answer. For the absolute best answer, you should wait until the final orbits are available for OPUS to use in processing a solution.
I have a clear view of sky. It is basically in a farm field and flat as a pancake. I sent in a couple data sets and the CORS sites used are 9.8 miles, 40.0 miles, and 47.4 miles away.
These are not final orbits
Ultra Rapid
OBS USED: 10648 / 11877 : 90%
# FIXED AMB: 57 / 65 : 88%
OVERALL RMS: 0.020(m)
Rapid
OBS USED: 12202 / 13678 : 89%
# FIXED AMB: 97 / 114 : 85%
OVERALL RMS: 0.023(m)
Make a study of it. Collect several 4 hour sessions and average the results. When you get to the point where adding an additional day's results don't change the average by a significant amount you have enough. Just guessing, I think that would happen after somewhere around 6-10 results.
When we site CORS stations we use a minimum of 10, 24-hour observations. I prefer three weeks. Once we provision a site, I will typically run 60 consecutive 24-hour daily files twice per year. My compatriot in these things (whose initials are L.A.) runs 90 consecutive daily files twice a year for 300+ stations. I won't out him, but he clearly is responsible for the big spikes in OPUS usage.
One trick in this, is you need to control the CORS sites that are used in the daily processing. Exclude those that trend poorly on the short term plots. If you have some bomber CORS (around here most UNAVCO sites are all golden and have data 24-365) include them. Try to use stations that will be available for your entire observation period.
And, if you end up submitting lots of solutions on a site, you will undoubtedly benefit from the [ http://x90gps.com/Tools.htm&apos ;">OPUS Accumulator. ] It is one of those things that if you need it, you really need it.
If you are interested in elevation, then it will be easier (since your site is secure) to just run 24 hour files.
Be sure to align the antenna north too.
I suspect that every 24-hour file will be within a 5 MM height of each other, but would not be surprised if the daily variance of your results closely mirror the short term plot for the nearest CORS site, and in some locations it is substantial. Take the nearest CORS to our office [ http://www.ngs.noaa.gov/cgi-cors/CorsSidebarSelect.prl?site=rbut&option=Time%20Series%20(short-term)&apos ;">RBUT Short Term ] it currently has 0.58 cm of stdev on the height and it's 24-hour solutions often vary by 2 cm on consecutive days. Since it is so close to our office, and has so much day-to-day range; it can really drag an observation around.
If a permanent CORS station suffers from 2cm daily shifts for it's 24-hour files and your expectations are 5 mm, the you clearly are going to need more than a couple of days worth of 6 hours files.
The difference between a 3 mm solution and a 3 cm solution is a boat-load of observation data. A big ship-load of observation data.
Mark
Surprised at 89% Obs Used and 85% Fixed Ambiguities if the receiver is out in the wide open. Those numbers aren't horrible but they're not great either.
Drilldo, post: 381206, member: 8604 wrote: I have a clear view of sky. It is basically in a farm field and flat as a pancake. I sent in a couple data sets and the CORS sites used are 9.8 miles, 40.0 miles, and 47.4 miles away.
These are not final orbits
Ultra Rapid
OBS USED: 10648 / 11877 : 90%
# FIXED AMB: 57 / 65 : 88%
OVERALL RMS: 0.020(m)Rapid
OBS USED: 12202 / 13678 : 89%
# FIXED AMB: 97 / 114 : 85%
OVERALL RMS: 0.023(m)
You have not said where you are. Given the distance to 3 CORS take some files, days or weeks apart, and split them into under 2 hour segments and submit to OPUS-RS. Request extended data and look for CORS that have high residuals and exclude them. You do want to be surrounded for OPUS-RS and your results can be improved by a far away CORS in the right direction.
OPUS-RS can use up to 9 CORS, but even if you have only 4 reliable, well situated ones there are benefits to using them.
Paul in PA
What are those three CORS?
Any set of coordinates in the right area can be used for multiple base observations over many years. The accuracy you require is from your base to your rover.
Paul in PA
Drilldo, post: 381182, member: 8604 wrote: Ok - thanks. I have already collected three five hour sessions because that is how long my internal batteries last and I didn't drag out the deep cycle.
I was thinking I might need a lot more but wasn't sure. Maybe it was sloppy work setting up the tripod as I didn't do it myself every day but on a recent job where we worked for ten days we collected opus data every day for at least 8 hours a day and when I processed them all there was about a 3" spread in the ten different solutions.
NGS 58 and 59
I would run cables or setup a waterproof box, put a laptop in and log 24 hour sets, then upload with an opus project id and run a combined solution.
Sent from my SM-G900V using Tapatalk
Shoot, you have three CORS right on top of you.......
Two sessions would be nice, one to get the number, the second one to confirm,,,,,
A third one to figure out if there is something imputed into your data wrong twice the same way....
It's always best to mix and match if you can......
And if you tie to NAVD88 you can find out the differences between OPUS and the bench mark system.
Paul in PA, post: 381223, member: 236 wrote: What are those three CORS?
Any set of coordinates in the right area can be used for multiple base observations over many years. The accuracy you require is from your base to your rover.
Paul in PA
The CORS it is using are
DF5391 TXLU LUBBOCK RRP2
DO8869 TXLA LAMESA
DO9484 TXL1 LITTLEFIELD
DO9608 TXP1 POST
I plotted up the first four solutions I have which range from four to six hours each and the max spread between any two points is 0.045'.
I would sign up for the OPUS Projects Manager webinar. I went to the live version of it. You will get a log in and then can start using Opus projects. One advantage of it is that you will be able to model the troposphere which opus does not take in to account. You will also be able to add all your observations into one project. http://www.ngs.noaa.gov/corbin/calendar.shtml
ftp://geodesy.noaa.gov/pub/opus-projects/OPUS%20Projects%20Processing%20Guidance%20-%201a.pdf
I would also recommend the OPUS Projects Manager. The online course is no cost and worth the time.