Issues getting a Fix

ndoring

New Member
Hi Everyone,

We often work in Marin County which generally consists of steep terrain and heavy to moderate tree cover. It has been my understanding that JAVAD should have no problem in such terrain. We have been having a hard time getting a Fix at certain locations (usually around steep terrain). I was wondering if people have been experiencing similar issues. The signal to the base station is 100% and we seem to have had enough satellites (generally 9 minimum if I recall correctly). Any insight would be helpful.

Thank you,

Nick
 

Shawn Billings

Shawn Billings
5PLS
I wouldn't say that the LS has no problem in difficult places, but that often works in places that others will not.

Is your base in a wide open place? This makes a huge difference. Some users see blue sky straight overhead and assume that is good enough. It's not. As best as possible we want horizon to horizon. It isn't usually possible and compromises must be made. But that's the goal. 9 satellites is a pretty low number when you consider that's the combination of two constellations.
 

Nate The Surveyor

Well-Known Member
Nick, it's ALL relative. Here are a few facts. You CANNOT get a "fix" in a well. There are places where even a Javad won't work. HOWEVER,

Check all the following:
Interference. I had a spot, on a job a few months ago, where NOTHING would fix. Turns out, that I was at a unique location, between 2 cell towers, that there was enough interference to shut me down. Move over 100', and all was normal. I imagine that there are spots like this, that will not allow enough GPS signal. Spots that are large. Use the spectrum analysis (5th button to the right, on top the LS) to see if this is it.
Use the satellite button (One button left of the middle button, on the collect / stake screens) and "Reset RTK" or "RESET tracking".

There are places with interference (noted above) where NOTHING works.
There are places were it will run slow. (waiting for satellite configuration to allow it to work).

But, it's the "Strongest game in the pile".

Another thing, one time, on a job, it ran just POORLY. OK in the field, but nothing spectacular. And, NOTHING in the woods. Turns out that I was NOT tracking the Russian Sats. Somehow, an upgrade, and reboot had left them off. I went home, hooked it to the internet, and got it working.

Anyway, what does your support team guy say?



N

PS
Shawn above is 100% right. You should for SURE set your base in the 100% sky. If possible.
N
 

ndoring

New Member
I generally try to set up the base in a place with the best sky visibility with the horizon in consideration when possible. For this project we have 2 days of GPS out there and set the base in two separate locations, After having issues the first day I decided to move the base to a more open area at the top of the hill. We were simply trying to have one technician collect a few topographic shots to compare the Lidar data we have for the area to our results. In an open flat area he was unable to get a fix even after letting it sit for a few minutes. The sky was open directly overhead but is surrounded by very tall and large Eucalyptus Trees. I am guessing those trees are the issue but thought JAVAD would be able to power through. I have attached a quickly put together image of the area and terrain to help explain the conditions.
 

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John Evers

Well-Known Member
5PLS
In addition to clearing NVRAM on the base, my first solution whenever experience tells me I should be able to get this shot, and it is not, is to perform a hard reboot on the LS. Press the power button for 13 seconds and it will completely shut off. Wait 2 seconds and turn the LS back on. This will correct any issues that originate with the LS.
 

ndoring

New Member
Thank you everyone for the input. I will be sure to try the suggested fixes. We are planning on going out there tomorrow and will take some time to test out the GPS.
 

Nate The Surveyor

Well-Known Member
Another factor, that could be affecting you is the recent solar flares are ADDING to the noise levels. I do not know for sure, all about stuff like that... but I have had VERY (With my old GPS system) good success surveying after the sun went down!
 

Darren Clemons

Well-Known Member
All the above are good tips/pointers. If none help it very well may be as Nate describes, just "one of those places". We've had a few here and there since becoming Javad users. Not really a pattern or explanation as they are not specifically usually in high interference type areas. Just kind of seem like Bermuda Triangles.....

My standard "this ought to be getting this shot" routine is usually something of a combo of what everyone's said.
1st - check the sky plot, are several sats right on top of each other? If you have 9 (and as Shawn says that's usually the bare minimum - 10 or more is definitely the magic number) and they are clustered together, the geometry is probably just too poor to acquire a fix.
2nd - reboot the LS - you should be back trying to acquire a fix within a couple minutes. That, as John says, will many times solve the problem.
3rd - If after reboot, I see the same "struggling" I'm probably heading back to the base to do Shawn's suggestion of clearing the nvram on the base.
4th - Is your radio signal strong (not the green 100% on the collect screen but the signal latency and strength in the radio parameters screen). Is the battery pushing the radio signal strong? Many, many days, towards late evening we will start "struggling" mightily to get shots - the battery gets weak and the radio signal carrying corrections becomes intermittent. Satellite numbers and geometry of course are critical but with all our years of RTK, the radio signal and strength are equally important, especially in coverage.

If all that fails - you probably just have an extreme area and/or some kind of interference disrupting things.
 

Darren Clemons

Well-Known Member
So if I can translate what Sibole is saying. If 9 is the true number we need mission planning on the LS. Matt is pushing it! Correct translation?
Mission planning on board would be a great addition. With the areas we're speaking of, down in 100-200' deep ravines, the situation is there may not be more than 8 or 9 visible at ANY time. That being said, it makes it crucial to know the best time to be at that point. Best thing is though, with the LS and PPK, even if you don't get a completed RTK you can still post process and have a trustworthy reliable coordinate.
 

Phillip Lancaster

Active Member
That is so true Clemons. Ndoring, you need to start collection on a float and over time you may be able to process this point through DPOS.
 

David M. Simolo

Active Member
I would just like to emphasize that in tough wooded ravine environments you might occupy a point for several minutes with seemingly poor results. Given enough time, things can turn around for you and patience really pays off. Yesterday for me 15-20 minute occupations were the key to good, verifiable results in the dense canopy. This will also improve your DPOS potential.

Your issues out in the open and not getting a fix sound like something else is going on, though.
 

Sean Joyce

Active Member
I am getting a sense that our enthusiasm is giving the wrong impression about the capability of this equipment with new or potential users.
I have some prospective buyers that I have to remind that this is still GPS equipment, the BEST GPS equipment but still has limitations.
If you can't get a position with Javad (and I would rather have it that way) then you probably would have gotten a bad one with other makes.

In regards to mission planning on board the L.S.;
WHAT IF there was mission planning on the Javad website and (given a local position where we will be generally working on our project) we could download a predicted satellite coverage file into J-Field for a time range, which had a new subroutine to display the data in relation to the present position in the field. (Maybe we could add estimated skymap horizon angles and directions while on point to fine tune.
This would detach us from the need to have cell coverage. Not perfect but this would help a lot to see if we might be wasting our time on a particular point.
 

Ron Booher

Member
I am looking to bid on a 400+ acre mountain ground with cover and a double tower(side by side) power line running through it, should I be concerned about too much interference from the power lines?
 

John Evers

Well-Known Member
5PLS
Ron,

I have never experienced any interference from AC transmission lines with my GPS gear. I have used my LS with the low point of a power line sag very close overhead. When I moved your fingers along the carbon fiber pole, or across the housing of the LS I could feel a strong 60 cycle hum. There was zero performance degradation to the LS.

I have however been stung in the eye when I leaned forward to look through the eyepiece on a T-16 while standing under a transmission line on a foggy morning. Not fun.

The T-16 that I now have was my fathers. It was a retirement gift the field crews gave to him. I think I now have the only T-16 with "enjoy your retirement" messages written all over it, residing under glass:)
 

Sean Joyce

Active Member
I am looking to bid on a 400+ acre mountain ground with cover and a double tower(side by side) power line running through it, should I be concerned about too much interference from the power lines?
FYI a powerline diagram. Like John I haven't ever noticed any interference but I try to avoid being under them if possible. I just took in a job where I have to locate some towers.
 

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