Questions about CORS solutions on a Leica SR530

Well, 2 hours and 4 minutes is pretty much the bare MINIMUM for OPUS Static. OPUS decimates your submitted file to 30 second epochs, so the “extra observations” (beyond ~248 of them) where not used by OPUS.

As far as what is “typical,” well, that depends on the “accuracy” (and realization/epoch) of the NAD83 Coordinates on the Passive Station, AND the accuracy of the coordinate estimates (and epoch/realization) on the CORS, AND just how GOOD the vector solutions where.

Basically...TOO MANY variables in play!

I generally see a centimeter (usually less) on repeat observations (6+ hours), but not all “HARN/HPGN” Passive stations are created equal. Some I “hit” very well, some not so well. Without knowing more about the area that you are in, AND the passive mark in question, I wouldn't dare venture a guess.

Bottom line IS... MORE TIME = more precision AND accuracy (relative to datum). The NGS requires a minimum of 4 hours for OPUS_DB, and I think that is a reasonable MINIMUM, with 6-8 hours being better (of course).

Loyal

For starters, I completely agree with Loyal.

As additional unknowns, we know that you have NAD83 coordinates, but to what accuracy? How were they derived?

I don't know if OPUS is now using dual frequency data for static observations. I've been away from it for a good while. If not, your 510 should do just as well. If L1 only, the ionospheric model computation comes in to play requiring a long observation float solution. With the recent space weather, that may be a factor.

I just don't know. Loyal is a much better expert than I am on that subject.

What I do know is that a 530 is one of the better, older, dual frequency receivers, very quiet, and very resistant to interference, except things like space storms, which are still not completely predictable in their effect any given day, on any given receiver.

I don't know if this was taken into consideration but the passive monument used in the OPUS observation probably was on an epoch date of 2007.000, while the OPUS results were probably in 2002.000 or 2010.000. If this was the case you can plug either the passive monuments info or OPUS solution into the NGS's HDTP computations.

http://www.ngs.noaa.gov/cgi-bin/HTDP/htdp.prl?f1=1&f2=1

Check Your Apples Versus Your Oranges

Your differences may well be in the recent changes in datum epochs.

General questions, what antenna are you using? Are you properly selecting it in your OPUS-S submission?

How good was your data?

With only 2:04 length of data you may also have a low number of satellites at the beginning of your file. A good suggestion is never start your OPUS submission with less than 6 satellites with clean data.

Convert your file to RINEX format if you have not already done so, then open it up with a text editor (not a word processor such as "Word") to view it. "WordPad" is OK. You want to see L1, L2, C1 and P2 data. Blanks were some of that data should be means you should delete data until 6 satellites have a full complement of all 4 observables. OPUS-S only uses the L1 and L2 but the lack of C1 and P2 speaks of the poor quality of the former.

If the data fills out at a point where you only have less than 2 hours, submit the file to OPUS-RS. In fact you may want to split your 2:04 file in half and submit to OPUS-RS even if it has better than 2 hours of data.

2 hours is the minimum OPUS-S accepts, but if you are looking for good elevations your minimum should be 4 hours.

Lastly did you do a GPS planning session prior to your observation to ensure you had suitable satellite geometry in the sky?

Did you have clear sky view to collect all of the available satellites?

Lately space weather and even atmospheric conditions have been less than favorable.

1 second epochs are a waste of your memory, 5 seconds is the smallest number you should use. 5 seconds should be compatible with any combination of COOP CORS should you wish to download and do it yourself.

Paul in PA

Thanks loyal, lots of good info in that post.

We ran in some control from a state survey job that was nearby, using their coordinates, which always seem pretty good.

I believe a few years ago I tried submitting the 510s data to opus, and got an error that it needed to be from a dual freq GPS.

Thanks, I'll definitely have to educate myself with more reading on that subject.

Check Your Apples Versus Your Oranges

Using the AT502 antenna, and yep, I selected it off the OPUS pulldown.

I'll take a look into the RINEX file for blank data to see if I had any issues there.

I'm still reading and learning a lot about this, I just learned today about OPUS-RS and it's newer computation model, I'm going to attempt to split the file to input it to that.

I did not do any GPS planning. I'm actually trying to find some GPS planning resources now.

The view of the sky was decent, but not perfect. No direct over head obstructions, but there were a few near the unit that could have created some multipath.

Thanks for the help and suggestions from all.

Mission Planning

Ashtech online web mission planning.

http://www.ashtech.com/web-mission-planning-2712.kjsp?RH=SITEMAP&RF=PRUEALMANACS

I believe other manufacturers have similar sites.

Also included in you Leica GPS software should be a mission planning program which would use the almanac you download from your receivers.

As to obstructions, chain link fence is a GPS killer.

Paul in PA

Check Your Apples Versus Your Oranges

For the length of time you need to observe, at least 3 hours and hopefully longer, mission planning is a '90s artifact as you will have plenty of satellites coming and going during your observation.

The only exception would be if you are under a major structure, which you will need to map for input into the mission planning software. Or just do what everyone else has done for 15 years: offset your points.

Mr. Zeiss Is Wrong

With OPUS-RS especially, planning is required. There are several times each day, albeit short, that the satellite geometry is weak. You have to know that time or you will have an observation or two with a very poor result. When I know that weak time I make sure I am set up and running a least 15 minutes prior and at least 15 minutes after.

Today in West Easton that short time was 11:45 AM to 12:45 PM. Good day to take a long lunch. Either that or a 2 hour+ OPUS-S from before 11 and until after 1. My Mission Planning says the PDOP was 3 but that is based on satellite numbers not there positions. At noon 8 satellites were visible but 6 of them were in a straight line from WNW to ESE, with the other 2 in the same general area with one low on the horizon at 15° very susceptable to complete blocking.

Too many today are fooled by satellite numbers not quality.

Paul in PA

Paul, you can call me Carl

The topic was static OPUS, not rapid static. NGS wants 15 minutes data for RS, two-plus hours for static. More is better.

I'm wondering how this all descended to a personal call-out to me for just posting the obvious.

Is there something personal?

A gap of a quarter of an hour or an hour is inconsequential in computing OPUS or other static observations which are set out from the start as being several hours in duration. Although NGS wants two hours minimum for static, it's obvious that more is better, particularly in periods of adverse space weather. None of that actually relates to mission planning.

Having been involved in survey grade GPS since 1992, I can say that mission planning has been a minimal factor for at least ten years. In rapid static, which I have also done since 1992, mission planning has been of little consequence since around 2003. If you are having problems with your equipment or procedure, don't single me out. I was factory trained in GPS. Were you?

Space weather is always a consideration, and that has been the major situation recently.

Not Personal Carl

Just trying to note what the response is to.

I have not had trouble with GPS when I make myself aware of problems. We are discussing a newbie to OPUS who needs to follow all the rules until he knows enough to ignore some at his own risk.

Using planning is a part of getting good GPS experience.

I have enough experience that even if I do not do pre-planning, I can look at the satellite sky view on start up, understand where the satellites will be in 15 or 30 minutes and plan my session according. It is too late to wait till you are back in the office and find your problems.

Paul in PA