For those of you who have had experience using both Base/Rover and VRS(or RTN)/Rover setup, which produces the best results? Thanks for any input/discussion on this matter.
> For those of you who have had experience using both Base/Rover and VRS(or RTN)/Rover setup, which produces the best results? Thanks for any input/discussion on this matter.
Both will produce excellent results, under the right conditions.
With a VRS system, your base is run by an administrator and your rover connects through an internet web site.
With your Base/Rover set up you handle everything and usually, you connect with a radio link.
With the VRS you can be at the mercy of the administrator (no offence to administrators, but the end user is relying on the service, 24/7 and you have to deal with that).
With a Base/Rover it's nobody's fault but yours, if things go south.
There is a good mix of +/- with both systems; they both take several batteries and if 1 is dead, and you don't carry spares, your pulling out the chain and plumbs; the Base/Rover is limited by radio range but you need a cell signal to make the VRS work, although I here tell of a cell signal booster or you could get a cell phone that uses satellites; neither one works vey well in canopy or urban canyons.
Radar
I've used a Trimble VRS network for about five years and a Leica SpiderWeb network for the last year.
I haven't been able to tell any difference between the networks. They have both been extremely reliable with only a couple of short outages that I can remember. Accuracy wise I have not noticed any difference either.
I couldn't imagine going back to the days of setting up a base station. If you live in an area with good cell coverage, networks are the way to go IMO. I seem to get better accuracies with the networks as well. This could just be because I have newer rovers and Geoid models than when I used to run a base.
We have used the NYSNET RTN system in New York for years...amazing results. We have even had similar traverse closure to when we used static for azimuth pairs. We can even get sub-foot under trees at times...and almost always sub meter in the woods.
It really comes down to knowing how to use GPS in general and it's limitations. With that said though...we use it every day and run rapid static checks on random RTN points a few times a month. In over 5 years of using this we have never had an error that was unacceptable for the specific project that we decided to use it on.
I have (2) base and rover setups: (1) Sokkia base and rover and (1) Topcon/Javad Legacy base and rover which I run with TDS 4.6.
I also have a Trimble R8 (Model 1) VRS which I run with Trimble Survey Controller 12.45.
I purchased all of my gear from my former employer when they shut down their survey department in 2008. The units now vary from 6-15 years old. Each have their benefits and detriments.
First, for convenience, I would prefer the Trimble VRS. I belong to a cooperative network which provide corrections over an internet cell phone connection. No base to setup and leave a field hand behind to babysit, and no base to breakdown at the end of the day. Too many people these days are interested in relieving you of your tools. I can be up and running almost as fast as I can hook up the rover rod, data collector, bipod and receiver. The limiting factor in my area of Central Texas Hill Country is cell phone reception. If I drop off in a ravine, there goes my connection. It takes a particular type of location/job to be able to use the VRS, and I do use it whenever possible. My Trimble will also collect a static file as long as I want, or until the battery runs out.
My Topcon Legacy(s) will record a static file for post processing while conducting RTK on an assumed (here) coordinate basis. The static files are stored internally and are downloaded from the receiver. Simple translation/rotation will shift the project to the final coords. I can also run "stop and go" static collection to be processed later. On these hot Texas summer days, my base will heat up and lock up and won't operate again until it cools down. I now pack it in a cooler with freezer packs to keep it running. From my inquiries, they are not serviceable anymore.
My Sokkias will either RTK or post process. No recording at the same time. I do not know if that is simply a limitation of the models I have (Radian IS and GSR2600) or if the newer Sokkia models can do both. Mine store static data to pcmcia cards to be downloaded and processed.
Sometimes I will use the Trimble VRS to average 3 or more long shots (180 epochs-each) to generate my base coordinate for one of my other units and take off and run from there with the base and rover. That is if I do not have the time/budget of collecting a static file for 2 or more hours.
I have eight acres and have set several control points in my "yard" to test my equipment on days when things are slow or I get bored. I have done this for over 5 years now. I am satisfied that ALL of the gear in my possession performs as it should with repeatable precision. I get acceptably consistent results when comparing between the VRS gear and the RTK base/rover setups.
As has been stated before, ensure you have good cell phone reception for VRS systems. I know of one vendor that carries simm cards from each of the cellular networks to cover his bases when he is out and about. And with the narrow banding for your RTK radios, I know of one firm that returned their new digital radio because it was not spec'd to operate above 99°. They went with the new "green" equipment and radios made by the man who is ill-regarded by some on this forum, but who makes excellent equipment.
Please do your homework and ask the vendors all of your particular questions, "will it do this", "will it do that", since you will be spending much of your hard earned $$. And have them demo'd!!! Really that is another consideration, with a VRS, you purchase a receiver for each rover you have and not (1) base receiver and (1) rover receiver. Some if not most offer receivers that can be a base OR rover.
Personally, I prefer a base/rover setup. I work over a large geographic area, and there are a lot of areas that I work that cell coverage is spotty. The Hipers I use have the spread spectrum radios, and are somehwat limited in range, but you work around it.
I have used a VRS system at my last job before I went solo, and I liked it. No base was required, and you could be up and running in about 5 minutes. That was pretty nice.
As others have said, there are pros and cons to each setup.
We have found the best result is to set the crew up with a base/rover and also being able to use the rover with VRS or Spidernet. That way there is always a backup. When our crews use RTN, the first thing they do is set a control point so that if the network goes down, cell coverage drops, etc. they can setup the base on that point and keep going.
I use the best of both worlds. My RTK base outputs corrections to a cellular modem which sends the info to my web-server, which serves them back out so my rover can access them. It's RTK will cellular instead of a radio.
The benefits of running your own base, knowing the details of control and set up, and the benefit of unlimited range of cellular. I'd highly recommend it.
They both have advantages. The one that I couldn't do without is logging a static file on my base and rover in adverse conditions for post processing later. I can get horizontal centimeter level accuracy in the woods, most of the time, with a long enough observation.
I like the VRS when I can use it.
No base; no stolen base.....
In my service area though, which is the entire State of Illinois, sometimes you can't get reliable cell coverage.
In that case you're stuck with the base rover if you want to do RTK GPS.
I agree with most of what the others have said, it depends on the circumstances. Personally I believe if you want decent repeatable vertical, and by that I mean within 0.05', you must use a Base/Rover set up. I just have not seen that from a RTN network.
I get 0.05' (vertical)on my network. At least on the areas I've checked into.
> I get 0.05' (vertical)on my network. At least on the areas I've checked into.
me too
> > I get 0.05' (vertical)on my network. At least on the areas I've checked into.
>
>
> me too
Me 3.
from our experiences, it seems that when we get true "network solutions", the precision is pretty comparable to setting up our own base, and in these cases it works just fine (and it sure is nice to not have to worry about a base getting stolen). If we are on the perimeter of the "network", it seems we only get a single baseline solution, and our precision decreases as the distance to the base increases.
> I get 0.05' (vertical)on my network. At least on the areas I've checked into.
The DOT in my area has a very tight network along their corridors; this is what I typically see too, when I check into one of their points.
Edit: I should elaborate on this: I own only 1 Rover and use a network almost all the time. There have been a few times that I recorded static data and sent data to OPUS.
Doug
I saw a couple comments regarding cell coverage being a limiting factor (true for both situations if you are using cell for your base rover).
An RTK Bridge (see BNB's "M3 RTK Bridge") is an effective way to remove limitations due to cellular coverage.
The RTK Bridge repeats the cellular signal via UHF to the rover and acts as a Wi-Fi hotspot at the same time. If you do VRS work, an RTK Bridge is a critical part to making it a reliable solution.
> An RTK Bridge (see BNB's "M3 RTK Bridge") is an effective way to remove limitations due to cellular coverage.
I might suggest rephrasing that to "...is an effective way to minimize limitations..."
If there's no cell coverage at the RTK bridge (or anywhere within miles of where you might want to situate it), there won't be any bridging going on. Some of us work well outside the range of cell coverage on occasion. Now, if you want to bridge a sat phone...
