What's the Glonass added value in canopy?

Sbaksso, post: 412786, member: 8769 wrote: is there any real added value for GNSS for surveying..... in canopy environment.

Absolutely. Slam dunk. No question.

Mostly it's just that more satellites increases that chance that enough are going to leak through the foliage to give a decent position.

Thanks Mark for your replay, in theory I guessed that just wanted to know from people who performed real job in real conditions, as I'm considering to purchase a new system so I was wondering does it worth to pay for GNSS options.

More satellites. Same multipath.

Big advantage. Well worth it.

1.) For the absolute best gps, never go in the woods. Always use static observations. A cluster of 6 units is quite strong.. Move one or 2 at a time. Then, after setting control, use an indexed total station, to shoot in the woods.
2.) For a bit weaker, but alot faster, use rtk gps, and total station.
Trouble with this, is the temptation to use rtk, in marginal areas. Now, we start getting some errors.
3.) Next on our lineup, is Javad gps.
It has the highest confidence in woods, of them all. It's what I have, and use.
A typical woods shot can take a bit of time, but, it has the highest confidence system I've yet seen.
4.) Is there one NOT to buy?
Well, I'd say, don't buy anything more than a year or two old. New is best.
And get a demo of 3 brands, in some woods, before you buy. Do some travel, if need be.
Because you are going to live with your choice, and your livelihood will depend on it, choose wisely.
Nate

Thanks Nate for your interesting points, I ve read something like that for Javad receiver somewhere, unfortunately I can't try it myslef because this brand have no dealer here. We have Trimble/Spectra, Topcon/Sokkia, Leica/geomax and CHC. the spectra dealer claims their SP80 can perform good results in forest surveying, I will ask him for for a test. As you said, I think up to date technology for multipath reduction matters more then the number of satellites.

What country are you in?

Here in the states, we have areas of isolation, where you sometimes have to travel a good bit for a demo too.
Also, some places on earth, don't have as good of satelite coverage, due to proximity to the poles. I know glonas orbits were meant to reach further into the polar regions.
But, ive not read anything recent on that.
N

think of gps satellite signals as arrows. think of your forest as well forest.
now set up a control point in the middle of the forest.
now ask 48 of your friends to get a bow & arrow and stand outside of the forest.
now ask them to shoot the arrow thru all those trees to where your control point
is located in the middle of the forest.
do you think an arrow will hit your control point?
i don't think so. maybe 1 or 2 would ricochet and hit your mark 1 or 2 or 10 meters off.
the arrow that ricocheted and fell 10 m off your point is your multipath error.
the arrow that would hit your mark dead center is your fix solutions
the other arrows that stuck on trees and ground are your float solutions.

now ask yourself, what are your chances of hitting the mark with your arrow?
there's your answer regarding Glonass/GPS signals.

I have CHC I think it has the same board as the Trimble units. 1 test I do for tough shots under canopy is to get a fix on the monument, dump the fix, tape in a nail 50.0 feet away, then get a fix on the nail. After all that I inverse between the 2, if the distance checks you should be good to go if not then you may need to try something different.

[USER=10211]@FrancisH[/USER], thanks for your replay, so actually Glonass or GNSS have no real added value, except in outside woods where classic Gps dual frequency signal is already good enough. Awaiting for Galileo's Signal witch uses a coded signal not phase measurement, so supposed to be resistant to multipath, GNSS is just like a car's extra option we pay for but do not use it.

Sbaksso, post: 412786, member: 8769 wrote: Hello guys,
My question is for GNSS surveying veterans, According to your experience, is there any real added value for GNSS (mainly GLONASS option as we dont receive Beidou in our area and Galilio is not yet operational) , for surveying in canopy environnement.

I used to work for a firm that had a set of Trimble R8 model 1s (GPS only) and model 2s (GPS + GLONASS). The model 2s were WAY better in the woods. The model 1s stopped working when you got near the edge of the woods, even with the leaves off. The model 2s could work most anywhere with the leaves off in flat terrain.

Anybody whos advice you use...find out what units they have, and in some cases like the r8 from Trimble, there seem to be a number of different "flavors" it comes in. Same model, different features.
Due to the expense of this type of equipment, many of us have a somewhat limited experience range. This is where learning from others can be invaluable. It also can be a slippery slope, if that person has a limited range of experience.
All gps seems to perform well, under wide open skies.
Even older gear.
Where it starts to show differences, is in challenging environments. Trees, and such.
Well, with modern gps, and as various technologies come to life, they are not all created equal.
There are advantages to staying with whatever data collector you are used to, such as shorter learning curve. However, a change in collectors may be in order, to get the most advanced system.

So far, the ones I'm aware of are:
Trimble/tds
Carlson
Leica
Topcon
And Javad... Who re wrote the data collector, integrating it with the gps, and radio, so that it's one unit.
So, it's diffecult to decide, when everybody wants your business, but you have to decide whose advice to follow, when those dispensing advice, have a limited experience range.

N

Here is a video I made.
[MEDIA=youtube]TAwPkR-1g2o[/MEDIA]
Glonass does help.
All the modern receivers are improving.
N

Thanks guys, I appreciate your comments and experience sharing.

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Nate The Surveyor, post: 412806, member: 291 wrote: 1.)
3.) Next on our lineup, is Javad gps.
It has the highest confidence in woods, of them all.

Sales talk? :p

How about truth talk?

Nate. That 0.12' H and 0.27'V needs to be explained. I can shoot a rebar on Monday with residuals like this and come back on Tuesday and have almost identical residuals but inverse and its 0.04' from each other. The greatest thing about Javad, I think, is DPOS and its simplicity on processing static sessions on every point I shoot each day. So easy! DPOS, 5Hz RTK and mainly the Javad Team. Only company that I know that actually listens to user comments and incorporates their suggestions in future software releases.

My motives for being happy with, and talking about my gear, are not monetary. As a business person, I'd be better off, keeping it secret.

I truly love my profession. And want others to benefit from what I have learned.

Since I don't work for any mfr, I have liberties to share my experiences.I have asked to work for Javad.

I did not sign any non-disclosure agreements...In talking with others, who have evaluated equipment, they SIGN non disclosure agreements, which means, they can't talk, like I do.

And, finally, if I find anything better, I will change horses. AND, if you have something better, I wish you'd share it with me.

I'd like to see the end users in the drivers seat. Not the snazzy, glossy, ads.
Is it ok to be altruistic, towards your profession, Above a particular brand? I think it's good.

I will also note, that I was a Topcon fan, when it was the best game going.

May the best be in the woods...in my hands!

Nate

Urban Canopy. Great results with GNSS.

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