>turn off the vertical solution with trimble for better /faster horizontal results?
Re-read how GPS works. There isn't a separate height measurement. It measures times/distances from the satellites and turns that into coordinates. The measurement time affects accuracy. The calculation time to go from measurements to LLH should be negligible.
The poorer accuracy for vertical is because you have satellites in all horizontal directions (with any decent constellation) but only up and none down to help with the vertical. Thus propagation effects don't tend to average out like the partially do on horizontal, and are harder to distinguish from true vertical differences.
I am using VRS and the Triumph 2 base. The VRS network does not give me as reliable results as the T2 base. When I am using the T2 base I can get a repeatable (verifiable) result just about anywhere.
Matt
:good:
That is something I was wondering about the LS, does it have the dynamic glonass inter-channel bias calibration?
I figure JAVAD has just started putting it in all units?
It's not listed as an option for either the LS or the T2.
To be honest, I don't know. I have not heard anyone say whether it does or not.
What I can speak to is the ability to be sure that you are getting good repeatable shots even in tree cover.
The J-field program that is running on the LS and the Victor LS has a feature called verification. You tell it that you only accept fixed solutions, then you tell it you want to verify anywhere from 1 to 500 times with between 1 to 6 different rtk engines. Once you have a fixed solution with the number of rtk engines you specified, it will dump those fixed solutions and reacquire the fix. It then averages the fixed solutions out and give you an overall rms value and a peak to peak error that was seen over the course of the verification process.
This is a game changing feature for anyone who uses GPS. A way to be sure you do not have a bad fix!
Matt
The issue with GLONASS becomes significant if you mix base and rover. My understanding is that the Javad receivers treat each GLONASS signal uniquely (the wavelength of each GLONASS satellite signal varies, unlike GPS). This creates a unique situation with GLONASS. If I understand correctly, the interchannel bias is to correct signals from other reference stations.
If you are using the same brand of base and rover, generally it doesn't matter, as this bias exists in both base and rover and the errors generally cancel each other out.
Sorry, when someone says "game changing" these days,it's usually BS.
Most of us here have been using RTK for years, some for decades. If you want to check your fix integrity, move 30', dump the antenna and re-fix in a few seconds and check again. It's not that hard.
Game changer? Be able to walk under trees, next to buildings, indoors and keep reliable RTK. That's a real game changer.
Lets keep it real here people.
> To be honest, I don't know. I have not heard anyone say whether it does or not.
>
> What I can speak to is the ability to be sure that you are getting good repeatable shots even in tree cover.
>
> The J-field program that is running on the LS and the Victor LS has a feature called verification. You tell it that you only accept fixed solutions, then you tell it you want to verify anywhere from 1 to 500 times with between 1 to 6 different rtk engines. Once you have a fixed solution with the number of rtk engines you specified, it will dump those fixed solutions and reacquire the fix. It then averages the fixed solutions out and give you an overall rms value and a peak to peak error that was seen over the course of the verification process.
>
> This is a game changing feature for anyone who uses GPS. A way to be sure you do not have a bad fix!
>
> Matt
Which is why I was asking if it is a feature, would lend some explanation as to why better results are seen with the T2 as base instead of VRS. Other than the obvious, that a local base with adequate sky view will perform better anyway.
I was also wondering if the T2 is set up to where the signal propagates to the chip at the same speed as the LS - this would negate the need for the GLONASS calibration (as you pointed out).
Simply being from the same manufacturer doesn't necessarily imply that the interchannel biases cancel.
A lot of VRS systems can see some error introduced due to using GLONASS. If I understand correctly, it's mostly because the cables that run from the antenna to the receiver will not be the same length at each location.
Of course there is also the possiblity that Leica, Trimble, Topcon also use some inter-channel bias compensation (now, pretty sure they didn't at first with GLONASS), and merely don't advertise it.
When I read the first hand account of user experiences on Javad's website, some of the testers are using their older base, or a different brand, or a Triumph 1 that they already had. I wonder if they are seeing the full potential, because I'm pretty sure that they are sacrificing solution performance for radio performance. Which may be OK for their application.
People have been mixing base/rovers for years since vrs, spider etc
How come all of the sudden this is a "problem"?
I use gps and glonass and hit my marks like I'd expect if I'm using vrs or spider or my own base.
> The issue with GLONASS becomes significant if you mix base and rover. My understanding is that the Javad receivers treat each GLONASS signal uniquely (the wavelength of each GLONASS satellite signal varies, unlike GPS). This creates a unique situation with GLONASS. If I understand correctly, the interchannel bias is to correct signals from other reference stations.
>
> If you are using the same brand of base and rover, generally it doesn't matter, as this bias exists in both base and rover and the errors generally cancel each other out.
you're so cynical... 😉
Most receivers, particularly of old, don't use GLONASS for the final solution because it was always considered less precise than GPS. Part of this reasoning related to the signal structure. For instance my old GPS/GLONASS RTK system did not use GLONASS to fix ambiguities. It didn't happen often, but there were times I had 10 satellites in view, but only five were GPS (and poorly dispersed), and I just couldn't get a fix. Newer receivers can actually fix on a mix of GPS and GLONASS. The Altus system I reviewed a few months ago required only 2 GPS satellites (I believe to address clock offsets) given there were enough GLONASS satellites available. I suspect Septentrio addressed the frequency differential of GLONASS satellites. I'm sure others have followed suit. Mostly this issue has been avoided in the past by only using GPS for the final position provided to the user and using GLONASS as a helping hand to maintaining a fix in marginal places.
And to be clear, we're probably talking about that last 2-5% of overall performance for newer receivers.
I work in some challenging conditions at times, and that last 2-5% is sometimes the difference between doing work with GPS and getting the robot out (and probably blowing budget).
For those that don't like GPS in the woods, you're right, it doesn't work at all. Don't dare try... 🙂
My crews have been pushing the GPS in the woods envelope for years, I wouldn't let every chief do it, for sure, but we get some darn good performance at times - usually using a mix of R8s and R10s.
I am really want to hear more and see pictures from those using the LS under canopy.
what part of the country are you in?
Pennsylvania, Kentucky, West Virginia, Virginia
I definitely see some canopy where current GNSS won't work on a regular basis. Often it has just as much to do with a large mass of earth blocking a large portion of the sky, like a ridge. I don't expect to be hardware-engineered out of that problem for another decade. Maybe L5 will help, who knows when we'll have enough L5 birds to make a difference???
Maybe you and Mr. Sibole could get together sometime...
As for L5 being of use in the field. I don't know. It's getting there, but those old satellites keep outlasting the design spec. I think there are five or six up there now and I think that 5 must be in view to be of a help. Not likely to happen right now.
Gavin,
There was an interesting article about a year ago in GPS World about a technique that used two antennas under canopy (perhaps a meter apart). Seemed pretty interesting. With the signals available, I'm not sure how much further tracking in canopy can progress. L5 could make a substantial difference though.
>we do live in exciting times...
agreed!
