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:
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.
@ Norman_Oklahoma
Aspirational. I had to look that up.
@ bm-nolan
The SureFix engine works by running two unique RTK engines in parallel.
I've heard JAVAD uses three RTK engines. We use network RTK. Does a base station always yield better results than network RTK? I've heard a base station does considering the close proximity of the base to the rover. However, is this the only reason?
I do not think anybody here will fault you for "trust, but verify" checking. Being a "doubting Thomas" in surveying can be a good thing.
That being said, we have had some good checks on it. We have pretty good results doing one/some of the following:
-running a base on site w/ SureFix
-checking at different times of the day on the same point (especially if in heavy vegetation)
-logging RINEX if we want a stop-and-go/PPK/static check on the point
-setting the HRMS to 0.015m (ie. the "rule of thumb" where 2 sigma's is double that as most manufacturers, per my understanding, show the HRMS at 1 sigma)
-setting 3 nails, RTK measuring them, and then hand taping to the monument. All 3 distance intersections are then the check on the measured coordinate of the monument.
-running GNSSAnalysis and getting it down to around the 0.02m mark (different times of the day even better)
-setting 3 RTK points, running a total resection of them, and noting the distance "schluff" in the calc (ie. if it's within your level of comfort, fire away; if not, a traverse may be in order)
Heck, we even double-check/measure with a total station every now and then 😉
If you are signing it, you have to do what you can sleep with. I will not ever fault anyone for doing what they consider to be their professional duty.
It seems my other comment got lost in the intarwebz.
For Chris-Bouffard:
I do not think anybody here will fault you for "trust, but verify" checking. Being a "doubting Thomas" in surveying can be a good thing.
That being said, we have had some good checks on it. We have pretty good results doing one/some of the following:
-running a base on site w/ SureFix
-checking at different times of the day on the same point (especially if in heavy vegetation)
-logging RINEX if we want a stop-and-go/PPK/static check on the point
-setting the HRMS to 0.015m (ie. the "rule of thumb" where 2 sigma's is double that as most manufacturers, per my understanding, show the HRMS at 1 sigma)
-setting 3 nails, RTK measuring them, and then hand taping to the monument. All 3 distance intersections are then the check on the measured coordinate of the monument.
-running GNSSAnalysis and getting it down to around the 0.02m mark (different times of the day even better)
-setting 3 RTK points, running a total resection of them, and noting the distance "schluff" in the calc (ie. if it's within your level of comfort, fire away; if not, a traverse may be in order)
Heck, we even double-check/measure with a total station every now and then 😉
If you are signing it, you have to do what you can sleep with. I will not ever fault anyone for doing what they consider to be their professional duty.
Doing checks, double checks and triple checks are fine, and I appreciate that you understand where I am coming from.
With all of the redundant checks, including using a TS, what time are you really saving over running a closed traverse?
I did see that you replied to me, but when I went to look for it, it was nowhere to be found. I appreciate you following up and reposting to me.
Well, we do not do ALL of those checks. We would typically do the following:
-run the base on site (most of our jobs also have a vertical component)
-log the RINEX (it does so in the background and does not greatly impeded average shot times with Carlson in my experience; this opens up a static or PPK/stop & go option back in the office if desired--if not desired, we keep the RINEX as a record of the work done as hard drives are cheap)
-set a tight HRMS
-run GNSSAnalysis
-sometimes measure at different times dependent on the day (ie. if there is a point under heavy cover midway down a line, hit it on your way up and hit it on your way back). My days of doing work in Northern Ontario are behind me (barring someone making a stupidly large $$$ offer) so there's usually an opportunity to check in on something. If not in the collection stage, one can always measure it when walking by if returning to monument things.
I would also caution that methodology of the tool is an important aspect overlooked. Just because one uses a closed loop traverse does not guarantee a more precise result. Just off the top of my head:
-are we in a mucky spring/fall?
-was the rod checked in a plumb jig or equivalent?
-when were the tribrachs checked?
-were nodal prisms used?
-was a 360 used?
-what's the centering accuracy of the prism?
-what degree off line of sight was the prism turned?
-does the prism have a reflective coating?
-how many seconds was the TS?
-were single, double, or sets of faces used?
-were short "legs" in the traverse predominant?
-what quality are the legs that the TS is set on?
-when was the TS collimated?
-what is the weather like?
-are we "flat earthing" in a mountainous area?
And I know that you know all of these things. I'm just listing them as that I am trying to illustrate that there are "many roads that lead to Rome." If one can retrace a boundary with RTK except one corner in the bush, is it cost effective to traverse the whole thing? Would it give a more precise result? Would it be "precise enough" per the regs and one's comfort level? Would a good, tight resection based off RTK points in the corner with one line of site run hacked through to the monument be a better use of one's time? Or would the RTK shot be "good enough?' I think one needs to examine what they are comfortable with and what they know their equipment is capable of on every job site before deciding the field work methodology.
Caveat: in Ontario, we do not have ALTA like specs required of us for our plans. Nor do we accept coordinates as a monument as in Alberta. And, unfortunately (fortunately?), the expected technical expertise expected of GNSS users here is FAR less than my, admittedly meager, understanding of an American PLS. Without going too far "down the rabbit hole" as this would not apply to anywhere outside of Ontario.......
Relevant GNSS info:
O. Reg. 216/10 Section 5
"Measurements and calculations for integrating cadastral surveys shall be proven by
mathematical closure of independent redundant checks. Positioning methods using a single
GNSS receiver require redundant occupations of a point using methods that result in
independent position determinations."
No acceptable methods to show independent position determinations are provided.
O. Reg. 216/10 Section 14
"The regulation was intentionally silent on whether the accuracy standards were referring to
“absolute (network) accuracy” or “relative (local)” accuracy. Although in the longer term
surveyors will likely strive to meet “absolute (network) accuracy” for now most surveys will be
striving to meet accuracy standards associated with “relative (local)” accuracy. This is
particularly true where surveyors are integrating using existing control that in itself may not
meet urban standards of “absolute (network)” accuracy.
(2) The coordinates required under subsection (1) shall be accurate, at the 95 per cent confidence level, to,
(a) 0.05 metres in urban areas;
(b) 0.2 metres in rural areas; or
(c) one metre in remote areas."
No acceptable procedures to achieve this are outlined.
The Ontario Survey Review Department (SRD) only requires a text export of one's GNSS coordinates to qualify as having met the requirement of raw GNSS data having been stored (ie. no RINEX, no .RW5, etc.).
I am not a GNSS expert--far from it. However, my general impression of the members of the Association is that they lack the technical prowess of our American friends. This is reflected in what is deemed acceptable for GNSS usage in Ontario. The Association simply has not put forth requirements nearly as stringent as those south of us.
