Carlson BRx7

Every RTK unit I've ever used, and I've used multiple examples of each of the big 3, yields a coordinate quality estimate. These are aspirational. A redundant measurement, preferably from an alternate base, is the thing to have.

"These are aspirational."

That sums it up nicely.

And, BTW, your idea of different solutions with the same results is essentially what JAVAD claimed with their approach.

Which leads to a kind of unrelated observation:

Unfortunately, the entire precision location through GNSS industry is predicated on exaggeration and secrecy and an intense desire to "black-box" and claim that their approach is best, but offer zero independent analysis that would prove this. Every test and lab analysis is cloaked with NDA's and vague assertions.

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I have been trying to break my javad for years.

It's pretty good. Not broken yet.

Nate

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I went out this afternoon with a solo guy to stake some property lines and another job for site plan. Anyway we he had the BRx6+. It was not a bad set up. It does seem clunky on all the steps to get connected to start the base and rover Bluetooth connection etc. I guess Trimble spoiled me in all that as it’s pretty seemless if you have the survey style or styles set up and ready. First time me running a Carlson surveyor 2. But me and the LS had a nice wet day and got what needed to be done done. He does want to test it in canopy soon so that will have to be another weekend for me to figure out its breaking points and how to best approach that. Redundancy is usually king when pushing any of them hard for sure.

Nate, I am a former Trimble guy who converted to Carlson. I considered Javad, but, at the time, I want an integrated GPS-total station-data collector work flow. When I made my switch, I felt most confident with Carlson. This is just me.

My focus was on the BRx7 GPS base/rover setup. I wanted to use it as much as possible. So, I was determined to use it in challenging situations. It hasn't disappointed.

To answer your question, Carlson uses a method it calls "SureFix". The Hemisphere S631 and Stonex S900 also use this method as they are essentially rebranded BRx7's.

SureFix basically uses all satellites available and calculates fixes with two different methods (algorithms). It then compares the two different solutions and uses statistical analysis to limit accepted solutions that maintain a precision specified in Carlson SurPC's survey style.You can also setup styles to include multiple sub-observations within an overall observation and an antenna dump at each sub-observation. You can set up custom styles with different precisions/techiniques/observation durations.

To sum up my experience, I would state the following. When I have checked my BRx7 GPS solutions with a gun, if SureFix says it's good, then horizontally it's good (within required survey tolerances). For vertical, I would say it's good 95% of the time. The other 5% I have found vertical error up to 0.15' in challenging situations. You just can't replace your brain with fancy equipment and software - we have to use our equipment responsibly.

Can you explain how Javad approaches its solutions and QA/QC methods?

Carlson's BRx7's and SurvPC use a method they call SureFix.

Surefix uses all available satellites and computes 2 different solutions from 2 different fixes. The two different fixes use different methods/algorithms.

Through the use of a setup survey style, observations can be of varying durations, have re-fixes at specified intervals, and require a certain precision in the two different fixes. This is all customizable.

When I first started using this setup, I ran several independent checks with a gun. In my experience, if it says SureFixed, horizontal is good. In a very few occasions, I had some vertical error up to 0.15'. So, be careful with the vertical in tough conditions.

Javad has been dividing signals, and developing fixes from differing points of view, for a long time. They finally came up with the idea that anything within 0.20' is a "Good Fix". I am not sure about vertical error allowance. The idea is that is the STARTING place. IF you are getting a shot on a power pole, or an old fence corner, usually 0.2' is good enough. Then, if you NEED more accuracy, leave it to cook longer. And, it can cook out most stuff. My usual goal for boundary work is 0.05'. But, it is a developing technology.

Nate

If a Leica, Trimble, or even a Topcon receiver is telling you that it is fixed you can rely on ±0.2' results. The questionable part is when they are telling you that the coordinate quality is 0.02', you may be actually getting anywhere between perfect and ±0.04', more or less. But a "fix" meaning better than ±0.2' is not unique to Javad.

Are you saying that coordinate quality is the RMS HZ and VT the precisions . I never heard that term used that way. Yeah when I am teaching guys in the field. I will often let them see it get down to the .02’ at DRMS then switch it to 95% confidence so they have and understanding visually that is not the accuracy. It’s an estimate at whatever sigma. They have set.

Understood. Those numbers are a statistic based on probabilities expressed in sigmas blah blah...... That's a coordinate quality estimate in my mind.

Its a statistic based on probabilities expressed in sigmas blah blah blah ..... THat's a coordinate quality estimate in my mind.

Carlson’s BRx7’s and SurvPC use a method they call SureFix.

I thought you had to subscribed to the Atlas service to get the SureFix. Does Carlson offer that service without an additional cost?

Running BRX7s without Atlas. Get SureFix all the time...

Carlson's Surefix is not a proprietary service that they sell. It is built into the hardware. I am currently using SurvPC which reports Surefix data in the DC.

I am aware Surefix is available in the other BRx7 antennas (Stonex S900, Benchmark S631). I cannot tell you how these other "differently" branded receivers or the softwares that are designed to use them function as compared to Calrson.

Carlson SurvPC has a GNSS Analysis function I have used. Still somewhat of a "black-box", but it purports to perform a least squares analysis and adjustment on the redundant observed vectors of a single point, giving you the most probable position. It also provides a supposed quality rating from 1-4, based on some unknown criteria. Quality 1 is 'City Center', but again, the specs for what the means is not provided.

That said, in my experience the results of this seem to pass the smell test. In the wide open, a few observations are sufficient to reach 'Class 1'. In more challenging conditions with higher HRMS, it requires more observations, and I can watch the rating climb from low to high as I provide more data and disable apparent outliers. After completing, you can export a report that has extensive statistical information, much of it beyond my understanding.

I think good field procedures are still a requirement (such as a time delay between sets), as it can only work with what you give it, but it does give you something you can hang your hat on. Unfortunately, at last test, using GNSS analysis precludes your ability to run a field least squares adjustment on the entire project.

Here's a write up on the routine:

https://web.carlsonsw.com/files/knowledgebase/kbase_attach/892/SurvCE30_GNSS_Analysis.pdf

Nothing beats good field procedures and survey "design" (redundancy with control point adjustment).

Just to add to this, the Carlson BRx7 is made by Hemisphere GNSS (the Hemisphere S631 is the OEM version, Stonex no longer has access to the Hemisphere boards since the acquisition of Hemisphere by CNH). The SureFix engine works by running two unique RTK engines in parallel. One is the Athena RTK engine, and the other their older version. Once the two engines are in agreement a fix is reported, with the idea that this eliminates any bad fixes.

My understanding is that GNSSAnalysis uses a procedure based off of "Kuusniemi, Heidi & Lachapelle, Gérard. (2004). GNSS Signal Reliability Testing in Urban and Indoor Environments. 2004" per Mark Silver's video on it.

The paper is listed here if you want to get into the "guts" of it:

https://www.researchgate.net/publication/255574236_GNSS_Signal_Reliability_Testing_in_Urban_and_Indoor_Environments

I seem to remember further testing was done inside an arena in Calgary, but it was many moons ago that I looked into it. I cannot remember if it was the velodrome from the Olympics or, stereo-typically Canadian, a hockey arena.

Nolan is one of the better resources for input on any Carlson GNSS receivers with a Hemisphere board as he works at their Calgary Benchmark office last time I checked:

https://www.youtube.com/c/benchmarkequipment

He, René, and David are all there in the pic of the "Benchmark Advantage" video on the Youtube homepage. I have had good luck with all of my dealings with them (don't let it go to your head, though, guys 😛 ).

I will never be convinced that any manufacturer is going to yield reliable results under dense canopy. Signals are bouncing all over the place and getting distorted before they reach the antenna. They may show you some statistical numbers but, in the end, it's all theoretical without the software approach knowing the density of coverage.

I'm not taking the chance of working under canopy with GNNS without field proofing the work with a TS. 0.2' +/- just doesn't work for me. In addition to that, vertical matters to me, I carry vertical on every job that I do because they usually turn into something either construction or environmental permitting related.

A used car salesman will always try to tell you that everything is good under the hood until you kick the dry rotted tires and they burst.