Dual frequency receivers, one or two?

Big Al, (Are you Al from Tool Time?)

If you have not done it yet, go and run for a day with somebody that has and knows how to use RTK.

Rtk used with in conjunction with logging raw data, for post processing, is a fine thing.

Nate

Al,

ONE L1/L2 receiver is all that you need to use OPUS (or post process into one or more CORS that are beyond L1 “range”).

One L1/L2 and a handful of L1(only) receivers can make a VERY productive and accurate system for MOST projects (LARGE projects might benefit from more than one L1/L2 receiver).

Unless you have L1/L2 post processing capabilities (the $1k key), the second L1/L2 receiver isn't going to do you as much good as it would if you did (for processing the inter-station “rover” vector). You could still do this (the inter-station vector) with L1 only, and that probably wouldn't degrade you solution any.

I would start with just ONE L1/L2 receiver (save the $1k for now), and watch for a screaming deal on another L1/L2 (or GNSS) receiver to come along in the future.

Loyal

Nate,

I am not from Tool Time. That's a good suggestion. Thanks.

Adding to Loyal's comments. You can process it yourself either with L1 only or dual frequency by downloading the CORS data, but that takes some time and effort. OPUS is pretty easy as long as it is up.

As Loyal mentioned: One dual frequency receiver will allow you to use opus. What that does is allow you to set it up at a convenient location on or near your job site and let it run for a few hours while you collect other data either conventionally or with L1 GPS.

- jlw

Thanks Loyal.

Let me make sure I understand your suggestion correctly.

If I purchased the L1/L2 receiver, but didn't purchase the L2 key for GNSS Solutions, are you suggesting that I would use the OPUS system to solve for the coordinates of the point occupied by the L1/L2 receiver, and then subsequently use this solution as my control in the GNSS Solutions software to solve for the coordinates of the L1 receivers?

Others here are much more versed with OPUS than me, but when I use it I just send one file at a time anyway. So I would see no reason that you using the file from your dual freq base, for each occupied point, would be any different that using a file from two bases running simultaneously.

Then you just leapfrog around with your ProMarks.

If the proposed base isn't Ashtech, how does working with other brands for vector solutions work out? It seems that you'd have another few buttons to push when you post process, and that stuff always makes me nervous. Trimble has conversions, but I've never done it.

Al

YUP...that's it in a nut shell.

See Jerry's more detailed resonpse below.

There are any number of possible combinations and configurations (of receivers/observations) that you can cook up to REALLY cover a LOT of ground with 1 duel-freq. and a couple/three single-freq. receivers.

Loyal

You're also suggesting I save my money for a second L1/L2 receiver instead of buying the L2 key. Is this so that I could eventually migrate to a dual frequency RTK system? I'd still need dual frequency post processing capabilities for the RTK system, right? Is your suggestion then to migrate away from GNSS Solutions for post processing? And if so, which software would you recommend?

Al

Thank you.

Wayne

MOST (if not all) receiver manufactures have "key-less" utilities to convert the receiver binary file (DAT/T01/PDC/GPS...whatever) to RINEX. And there is always TEQC which will convert most (but not ALL) files to RINEX.

Mixing and matching receivers IS more trouble than running same-o/same-o, but it is RARELY a problem once you get the hang of it (and convert EVERYTHING to RINEX).

I have processed networks that have dozens of [rover] receivers from at least four manufactures before, and it isn't really all that bad.

Loyal

Do you process all your vectors in Solutions? Do you export the vectors and put them through an LSA program so you can mix in other types of measurements?

Didn't think so

I've just been spoiled and never had to even think about doing it. It's just that any time an extra step needs to be taken, the potential is there for something to cause grief.

And I get the impression that our poster is still on a substantial learning curve. So it's good he's asking these questions on this awesome source of information: beerleg

Al

Well...Yes, No, No, Dunno...

You don't need L1/L2 post processing software to run RTK (the vector processing is done by the RTK engine in the receivers, and the coordinate projection stuff is done in the collector).

Realigning yesterdays RTK data (shot from a fagarwe position) to the OPUS results from that observation processed today, isn't really all that difficult. Some software will do it for you, and even if it won't, you can probably whip up a speadsheet routine to get the job done with enough accuracy for RTK purposes. I have a BASIC program that I wrote years ago that I use for this purpose all the time.

At some point...I'm sure that you will want L1/L2 processing capabilities, but that might be a ways down the line. You can certainly get by without it in the short term. I don't use GNSS Solutions, but I have heard good things about it, so I would stick with it if I were you.

Bear in mind that ALL of the Post-Processing Software will need (actually already does) some upgrades to properly handle the IGS08/NAD83(2011) change in the NSRS this year (or early next). For some software this is minor (antenna calibration files), for others it might be a little more complicated.

Some software is pretty much there already, some is not (your mileage will vary).

Loyal

Hey Mr. Big Al, I have a couple Trimble R8 L1/L2 receivers that I have been running on a VRS network, thay are in good shape and for sale at a very reasonable price, am willing to split up the pair. If you wish post an email or send it to the email address in my profile and I will send pics and more information.

Joe

I mix OPUS vectors (from the G-FILES), with L1 & L1/L2 vectors generated by one (or MORE) post processing packages all the time in COLUMBUS (you probably do something similar as well, doesn't everybody?).

It's the only way to go IMO. I even extract the OPUS vectors on a SINGLE OPUS solution and run them through COLUMBUS!

Loyal

We live in an amazing time for GPS, thanks to all the real time networks and CORS stations. A side effect of all the RTK networks is their base station data.

I've never used anything yet but one L1/L2 receiver and a combination of OPUS-RS and the free Topcon Tools demo license (allows 5 stations, including the "rover"), along with freely available CORS and base station data from several regional real time networks.

Most of what I do is semi-urban and there are enough CORS nearby to use OPUS-RS and 45-90 minute occupations for just about everything.

in WA we also have that amazing WSRN and its Rinex Shop, where you can download WSRN base station files to use with your post processing software.

I like having a quick & dirty position from OPUS-RS that I can use for fieldwork/recon and then using topcon tools to do my own processing using either CORS or WSRN base stations. Might even wait for the precise ephemeris and run it all again just out of curiousity. And in the end the horizontal never varies by more than the proverbial .04' -- Vertical is another matter, if you need tight verticals use the local base station data. The verticals are clearly a lot tighter from the WSRN when compared to OPUS-RS, 1-2cm vs. 4-6cm.

OPUS-RS is really finicky about clear skies, does not work if there is even a hint of canopy or urban canyon, so that's what led me to start learning post-processing. Most of the time if OPUS-RS rejects a file I can still get a fixed solution using the WSRN base stations.

Every time I use OPUS-RS or WSRN I think for a moment about how many crews, trucks, and receivers it would take to do that on my own, and I'm really thankful.

I have done all my post processing thusfar in GNSS Solutions. I have not really put the results through a least squares program for mixing in other types of measurements, but I like that idea. I have Land Desktop 3, which has some LS functionality, but my knowledge of it is limited, and I'm not sure it'll do what you're talking about.

> Do you process all your vectors in Solutions? Do you export the vectors and put them through an LSA program so you can mix in other types of measurements?

Didn't think so

I'd say I'm on a learning curve. This forum is awesome. Thanks.

WSRN sounds good. I don't know of a similar system here in Massachusetts. KeyNetGPS is available, but costs $3,300 per year for a subscription, last I checked. That's a bunch of change to me, especially if only for occasional use. I'd be interested to know if there are other real time (VRS) networks available to me, especially if they are FREELY available.

But, I agree with your sentiment, even if only using OPUS. It is an amazing system we have available to us.