STATIC vs RTK [Poin...
 
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STATIC vs RTK [Point Occupy Time]

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(@therock003)
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When opting for RTK you stand on a given point for no more than 5 secs and you can instantly take a shot, but when recording a static log file on both the base and the rover, you need to stay at least 15 mins (depends on the baseline) to get an accurate solution.

?ÿ

Why cant you solve the baseline with 5 secs in the same way, but with post processing. I mean on my head i think of RTK as a live post-processing procedure where the base broadcasts corrections on the fly. Why can the same take place when you go for static post-processing

 
Posted : January 2, 2018 11:12 am
(@kevinfoshee)
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"Why cant you solve the baseline with 5 secs in the same way, but with post processing."

That's what RTK does...It just solved your baseline on the 5 sec shot. I don't understand what you are asking?

 
Posted : January 2, 2018 12:28 pm
(@paul-in-pa)
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RTK is a nearby solution from an already resolved GPS coordinate point. The base transmits a correction assuming that the coordinates were it is sitting are correct. RTK will give you a position based on very few GPS observations from sometimes very few satellites. It can sometimes give a repeatable position at a later time but if you do not observe RTK points at least 3 times you will never know how good it is not.

Static observations of 15 minutes can sometimes fix a position from no nearby known control, but again if you do noy repeat the observation what do you really know?

Using a here position and post processing the base position later can combine both aspects and typically your base is occupied much longer than 15 minutes which in itself is a good check on your work.

I would surmise that from the nature of your question you are someone who just turns on the machine and pushes the right buttons without any knowledge of what is going on inside that very complex computer we call GPS, which in those 5 seconds has gathered upward of 2,400 independent GPS measurements, analyzed and adjusted same and gave you a simple 3 coordinate XYZ answer.

Paul in PA

 
Posted : January 2, 2018 12:46 pm
(@therock003)
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Well when the tolerance required is not that tight and it concerns a small local area you can get away with RTK. My Question is when RTK is not available for whatever reason (Receiver is out of RANGE or communications are jammed between the base and the receiver), can you get same results practicing static calculations on each pointrequired?ÿ by logging in under a minute for each point, the same way you would have done if you were performing RTK

 
Posted : January 2, 2018 12:55 pm
(@rankin_file)
Posts: 4016
 

You can- google post processing kinematic survey.

What type of processing software do you have, and how familiar are you with it?

 
Posted : January 2, 2018 1:13 pm
(@therock003)
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I use TBC for normal post-processing scenarios when accuracy is required. Havent practiced PPK before, but i believe time has come that i must learn of its use and practice. If PPK is the RTK equivalent then it is what i am now asking and looking for

 
Posted : January 2, 2018 1:18 pm
(@rankin_file)
Posts: 4016
 

Good- Unavco has a tutorial out there for older model receivers and TGO that Iƒ??m sure you can adapt and use with your gear. Good luck. (Disregard the crumudgeons- this is a good place to ask your questions)

 
Posted : January 2, 2018 1:29 pm
(@paul-in-pa)
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OK, I assume you have an RTK base set up but need to get a point?ÿ from somewhere where your base is not talking to the receiver. For that you need to understand what all your rover can do, i.e. can it store raw field observations for later post processing, which may be outside the parameters of your rover and controller capabilities. For RTK your rover may be using data points 0.1 seconds apart, but that may not be the default for storing data. Typical OPUS & OPUS-RS data is collected at 30 second epochs, hence the need for a 15 minute observation. Your Rover if it has raw data storage may be at 1, 5, 10, 15 or 30 second intervals. The shorter the interval the less overall time needed to store. Off hand I suggest 1 minute to 5 minutes. We need more info to fully answer your questions.

Paul in PA

 
Posted : January 2, 2018 2:00 pm
(@nate-the-surveyor)
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Posted by: therock003

When opting for RTK you stand on a given point for no more than 5 secs and you can instantly take a shot, but when recording a static log file on both the base and the rover, you need to stay at least 15 mins (depends on the baseline) to get an accurate solution.

?ÿ

Why cant you solve the baseline with 5 secs in the same way, but with post processing. I mean on my head i think of RTK as a live post-processing procedure where the base broadcasts corrections on the fly. Why can the same take place when you go for static post-processing

I do understand your question. (i think]

Rtk works in 5 seconds. (sometimes)

Why does static take 15 min?

My take is:

Since rtk is tracking sats, in a continuous data stream, the 5" shot, is really a little sample, out of a stream. It was "fixed" as you walked up to the point where the 5" sample was taken.

But, with pps (post processed static), there was no stream.

You had a reciever in the off position, as you walked up. (a moving rover with rtk, that remains fixed, or locked while moving, has checks built in)

But, a static unit does not have this benefit. Set it up, turn it on, and it starts from scratch. Solve it all. Sometimes, ot gets it right real fast. But, sometimes no.

So, 15 min is a "safe bet", so your confidence levels are higher.

You can do real fast static, and it get it right, but not consistently.

(maybe it will help you move mentally in the right direction)

N

?ÿ

 
Posted : January 2, 2018 2:07 pm
(@nate-the-surveyor)
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In open areas, with dual freq, 8 min is often adequate.

 
Posted : January 2, 2018 2:10 pm
(@dave-karoly)
Posts: 12001
 

RTK is working from an initialization already calculated and slightly looser tolerances (typical 1 cm).

Every Static observation is initialized independently which is why it takes longer and the tolerance is typically 5 mm.

PPK is the post-processed counterpart to RTK.?ÿ A continuous file is stored which the processor will attempt to initialize then all the separate observations in the file share.?ÿ If it can't initialize the file then you are out of luck.?ÿ RTK has the advantage that you know in the field that your survey is initialized.

 
Posted : January 2, 2018 2:11 pm
(@totalsurv)
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Good question worth asking. I think the first few replies didn't get the question and went off on a lecture.

 
Posted : January 2, 2018 2:20 pm
(@therock003)
Posts: 189
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Posted by: Paul in PA

OK, I assume you have an RTK base set up but need to get a point?ÿ from somewhere where your base is not talking to the receiver. For that you need to understand what all your rover can do, i.e. can it store raw field observations for later post processing, which may be outside the parameters of your rover and controller capabilities. For RTK your rover may be using data points 0.1 seconds apart, but that may not be the default for storing data. Typical OPUS & OPUS-RS data is collected at 30 second epochs, hence the need for a 15 minute observation. Your Rover if it has raw data storage may be at 1, 5, 10, 15 or 30 second intervals. The shorter the interval the less overall time needed to store. Off hand I suggest 1 minute to 5 minutes. We need more info to fully answer your questions.

Paul in PA

Well i operate on Europe, OPUS is not an option and besides i dont use CORS whatsoever. I have set my own base, on a known point fixed on a rooftop and it sends corrections. Since it is an island with a small radius, i want to account for possible miscommunications between my base and the receiver. I made a topic about this

https://surveyorconnect.com/community/gnss-geodesy/gnss-radio-communications-jammed/

But anyway whatever the case may be, since the baseline is short inside the island at most cases, and i have unlimited access to the base, i dont see why i cant do this PPK and get things done

 
Posted : January 2, 2018 2:27 pm
(@norman-oklahoma)
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?ÿ...Why cant you solve the baseline with 5 secs in the same way, but with post processing....

Very often you can get short static baselines - as short as RTK vectors typically are - to resolve with very small data sets.?ÿ Trouble is, you don't know if it's going to resolve or not until much later, so you collect enough data to be certain that it will.?ÿ Which may be many times the minimum necessary.?ÿ

 
Posted : January 2, 2018 3:53 pm
(@paul-in-pa)
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There are limitations to a single base station that are best overcomer by longer occupations. The advantages to OPUS are multiple bases. The advantages to OPUS-RS are multiple bases that surround the solution allowing a better interpretation of atmospheric conditions which reduces the time required.

How small is your island? One method of checking yourself is to establish by long term observations fixed points near the limits of the island that you can check into before and after an RTK?ÿsession. But having done that there is no reason not to use those points for your RTK base observation.

The key to RTK is that the base is near the job such that the atmospheric conditions are minimally changed between the two.

Paul in PA

 
Posted : January 2, 2018 7:49 pm
(@therock003)
Posts: 189
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Posted by: Nate The Surveyor
Posted by: therock003

When opting for RTK you stand on a given point for no more than 5 secs and you can instantly take a shot, but when recording a static log file on both the base and the rover, you need to stay at least 15 mins (depends on the baseline) to get an accurate solution.

?ÿ

Why cant you solve the baseline with 5 secs in the same way, but with post processing. I mean on my head i think of RTK as a live post-processing procedure where the base broadcasts corrections on the fly. Why can the same take place when you go for static post-processing

I do understand your question. (i think]

Rtk works in 5 seconds. (sometimes)

Why does static take 15 min?

My take is:

Since rtk is tracking sats, in a continuous data stream, the 5" shot, is really a little sample, out of a stream. It was "fixed" as you walked up to the point where the 5" sample was taken.

But, with pps (post processed static), there was no stream.

You had a reciever in the off position, as you walked up. (a moving rover with rtk, that remains fixed, or locked while moving, has checks built in)

But, a static unit does not have this benefit. Set it up, turn it on, and it starts from scratch. Solve it all. Sometimes, ot gets it right real fast. But, sometimes no.

So, 15 min is a "safe bet", so your confidence levels are higher.

You can do real fast static, and it get it right, but not consistently.

(maybe it will help you move mentally in the right direction)

N

?ÿ

This is gold. I will savor all of this information, as it really answers my intended question

How fast can i practice ppk do you think and be reasonably safe that i have not come with unsolvable calculations. 15 mins going for a 60 point plan, is crazy, id better go with total station shots

 
Posted : January 3, 2018 12:16 am
(@duane-frymire)
Posts: 1924
 

My understanding is it has to do mostly with the ionosphere delay.?ÿ ppk has to run long enough on each point to solve the delay at that point, whereas rtk knows the delay from the base broadcast.?ÿ But for short baselines of a couple miles the time shouldn't really be much more than rtk.?ÿ

 
Posted : January 3, 2018 6:40 am
(@spmpls)
Posts: 656
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There is a very recent paper, published in the ASCE Journal of Engineering Surveying, that contains some very interesting and surprising (encouraging?) analysis between static and RTK (RTN) positional accuracies and occupation times. It can be accessed here, although it may require a subscription:

https://ascelibrary.org/doi/abs/10.1061/%28ASCE%29SU.1943-5428.0000244

An earlier version, captured in the Masters Thesis of one of the authors, can be accessed here:

https://ir.library.oregonstate.edu/concern/file_sets/7p88ck96s

 
Posted : January 3, 2018 7:09 am
(@mightymoe)
Posts: 9920
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There is no problem with using PPK to locate points when you don't have radio for a RTK session.

You don't need to occupy the points for 15 minutes or an hour or 4 hours to get as good a number that you will get with RTK.

PPK, RTK, Rapid Static, Static, Fast Static are essentially the same thing, with PPK you calculate the number in the office with the office computer, with RTK you do the same calculation in the field with the field computer.?ÿ

The data is the same data, it's not a mysterious process, there are just a few procedures that are different.?ÿ

The big difference with RTK and PPK is the time it takes to fix. The old recommendation time to allow PPK to fix for a session was 8 minutes when you have 4 or more sats up. I have turned that back to 3 and never had an issue. For one shot that means that you need to spend 3 minutes plus the time on the point, if the base is close (under 10 km)?ÿtreat it as you would a RTK shot, for longer shots over 10 miles then 10 minutes plus one minute per mile. That is also a bit over the top, but you won't go wrong using that rule of thumb.

The nice thing about PPK is once you do get it fixed you can leave it fixed and work all day long or until you lose lock, then you need to refix for the 3 minutes. So fix in 3 minutes, locate 10 points with the times you feel comfortable with or you can even do a continuous topo in PPK.

TGO had a setting that put a minimum time for a single PPK shot at 2 minutes, it was necessary to turn that back to whatever time you wanted to make the PPK shot process, I'm not sure about TBC, I usually use PPK for a check on property corners or continuous topo.

The K in RTK and PPK of course means kinematic which means moving and you can collect data on the move with both of them, but most people use RTK as RTS or real time static same with PPK, most of the time it's used as PPS or Post Processed Static, which of course is Static. Usually people don't move as they are collecting PPK, but you can if you want.

Create a PPK style, I use 5 seconds to collect data, but you can use whatever you like. I will set a minimum of 3 epochs for a topo shot, so you have to at least give the shot 15 seconds, I usually will give them 45 or more. For topo I also collect at 5 seconds, the base and rover have to be in sync, you need to be collecting at either 1 second or 5 seconds at the base for it to work with a rover set at 5 seconds. And as always it best to have good open sky, under trees you can have issues and you wont' know until processing.

I don't ever collect PPK in the receiver, always in the DC, less issues that way.

Give it a try, it's really not a big deal, collect a set of points in PPK in your parking lot, then in RTK, I bet you will like the results.

?ÿ

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?ÿ

 
Posted : January 4, 2018 3:03 pm