Accuracy Issues

Adam Davis

Member
Hello all, I've had the Javad Triumph-LS and 1M system for a little over a month and after much trial and tribulation I cannot seem to get the Javad to shoot a single check point consistently without an error of around .06' My current boundary settings are 150 epochs/240 seconds/Only RTK Fixed/Verify with V6 Reset/Confidence Level 15/Confidence Guard .131/.023/Consistency Level 30/Minimum RTK at least 2/Validate ON/Correct for Tilts Off.

I set up my 1M on a known base point (the only one i have used throughout the job) and orient it north. I also orient the LS north. The pole was just calibrated. I am trying to take as much potential human error out of the equation that I can. Maybe I am expecting too much but when I shoot the same monument 2 hours apart the results are .06 different. Granted I have got some shots to be .01-.02 but not with the amount of consistency I would like. Am I missing something? I understand I can take multiple shots and average them out but I am looking to be able to set monuments with the LS in real time and not worry that they are potentially almost an inch away from where I say they are. Sorry for the long winded question, I look forward to any replies! Thank you!
 

Sdrake14

Active Member
Hi Adam,

Are you using the level offsets function on? If so it needs to be calibrated every time you start the base. From my experience I was seeing dirt like this from that oversight in the past.

On the other hand....hmmm...lets see 2600/0.06 = 1:45,000+/- right? If I had that and didn't have to traverse I'd be like... bang! Even if it was single shot with the total station, come back tomorrow and if I saw 0.06' difference I'd call it systematic.... now this is just me...

Adam is the tolerance you are expecting required for the job? What specification are you working under? If I expect more out of my work than required than I am wasting time. Or if you need geodetic tolerances then you possibly need a different method, say static baselines with post processing.
 

Aaron S

Active Member
Adam: I think your results are fairly good for GPS in general, but now that I use the Triumph LS, I/we have higher standards.

I've gotten to the point with my LS that anything that checks outside of 0.04' causes me concern. My check shots are generally within 0.03' consistently while using RTN - even in poor conditions, and without even trying too hard.
 

Aaron S

Active Member
By the way, I didn't realize it matters which direction the rover or base were oriented. I thought that was a thing of the past? How does that affect the results?
 

Adam Davis

Member
First off, thanks to everyone for their replies.

Matthew, is there a specific reason you asked about the monopod?

Sdrake, the tilt correction is off, I already went through that bit of a rough patch thinking I could keep it on all the time. I understand 1:45,000 is spectacular but that's not necessarily what i'm getting. I'm looking to set 2 control points to work off of in order to set monuments on the very far side of the job without having to traverse it. They are approximately 200' apart. My first control point difference between the two shots 2 hours apart was .03 which is acceptable but the one i'm having an issue with is the second which is .06. They were both open areas and I'm just confused on how one could be double the other error-wise.

Clifton, It's not something that we typically do but we were looking to help mitigate any potential problems.

Aaron, what does your boundary profile set up look like?

James, where did you read or hear about the 600 epochs? I generally have about 1100 epochs over my 240 seconds on the shots.

Matt, what length of time do you suggest? I look forward to testing that out.

Everyone, do most of you use the monopole and J-pod? Also is there a functional purpose to the flashlight blink feature?

Thanks again, very much appreciated responses, like Nate says, the Javad community is incredible.
 
Last edited:

Shawn Billings

Shawn Billings
5PLS
My own testing leads me to believe the precision of the Triumph-LS to be about:

"He(RMS) = 5mm + 0.7ppm x BL and Ve(RMS) = 10mm+0.7ppm x BL

This is not Javad's specification, this is my own observation using 240 second observations at 1 Hz. I determined this before Beast Mode was released. A 15.9 mile (25.6km) vector would have a potential horizontal error at 1 sigma of 0.075' (0.023m), a vertical potential error of 0.09' (0.028m). For the 2 sigma error you would multiply the 2D by 1.6 and the vertical by 2, so that would be 0.12' and 0.18'. Again, this is all based on my personal observation and not Javad's published specifications. But it certainly appears to be a pretty good rule of thumb."

From: https://support.javad.com/index.php?threads/dpos-vs-long-range-rtk-15-9mi.1495/#post-12979
 

Shawn Billings

Shawn Billings
5PLS
You've been given some great input.

Matt Sibole's mentioning of the monopole is worth considering. It's possible that there is some eccentricity in the pole at one of the joints. The best way to tell this would be to find a sturdy shelf about 5' above a smooth floor and drop a plumb bob from a mark on the bottom of the shelf to the floor, then mark the floor. Extend the pole till it compresses between the floor and the shelf. Calibrate the bubbles, then turn the pole 180°. If the pole is straight the bubbles should still be centered.

However, you mentioned that you maintain the orientation of the LS during the observation, which would likely cancel out any error due to eccentricity provided that the eccentricity in the joint(s) is consistent. If the joints are wobbly, then you've probably found your problem.

As Matt Johnson pointed out, from a statistical point of view, the best estimate for the true position of the point (which is never truly known) is the average of the two which would suggest that each has an error of 0.03'. From my own testing, I'd generally expect the accuracy (at 2 sigma/95%) to be 0.027' for each of these observations. The repeatability of two observations on the same point with an accuracy of 0.027' in each observation would be 0.038', so your 0.06' does seem a little high, but not unbelievable. (Note that my accuracy estimate does not include centering errors.)

Lastly, keep in mind that the discussion of epochs largely comes from a time before beast mode and thus epochs and seconds are virtually interchangeable. Of course, two epochs over 4 minutes is not the same as 240 epochs over 4 minutes or 1200 epochs over 4 minutes as are more data points to average. But time is still important, which means that 240 epochs at 5Hz can be done in 48 seconds but isn't going to be as good as 240 epochs over 4 minutes.

In my own testing, I found that there is a point of diminishing returns with more time on site. The difference between the accuracy of a 30 second observation and a 4 minute observation was about 10-15% (if I recall correctly). Past 4 minutes, the accuracy improves very little, even out to 20 minutes.
 

Jim Frame

Active Member
Everyone, do most of you use the monopole and J-pod? Also is there a functional purpose to the flashlight blink feature?
I don't use either, preferring a Seco carbon fiber pole with a 10-minute bubble and a Seco bipod. I have a Leica quick-release connection on the pole and the Triumph-LS so I can use the same pole with a prism when operating with a total station. But I typically work in places that don't require packing equipment in on my back, so having a pole that collapses to just a couple of feet isn't valuable to me.

With regard to the flashlight blink, I think it's intended for use when the receiver is above head height so the operator can tell when the shot is stored.
 

Aaron S

Active Member
Aaron, what does your boundary profile set up look like?
I have mine set to 360 seconds and 300 epochs, with the usual verify & reset of the factory settings. However, I usually end up getting way more than 300 epochs during that time.

I use the J-Pod for long hikes & backpacking, and a Seco carbon fiber with bipod for short trips near the truck.
 

Jim Campi

Active Member
I have mentioned this several times with little to no interest. One more shot. I noticed immediately that the LS time to a fix and total fixed engines is correlated to the Azimith of the LS. Rotating about a point can mean the difference of multiple fixed engines per shot as well as the time to a fixed solution. In my view that can translate to minutes per shot under a canopy. Has anyone else noted this and is this an expected behavior?

Sidebar: My 18 year old daughter assists me from time to time when not in school and she noted the same on her first use of the equipment.

Is it best practice to orient the LS with an Azimuth of 0 degrees (assuming the base is oriented in the same direction)?

Presumably, fewer fixed engines under a canopy could have decreased accuracy?
 
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