Norm, one of the early (maybe the earliest) drivers of machine control were the great PRB coal mines. They would do presentations about it frequently. One of the construction companies that worked in the PRB moved to a coal mine in a more mountainous area. Chaos ensued.
After doing a 200 sq mile mapping project they decided to design and construct a road 6 miles south, holding their mine calibration. I think they picked up about a foot per mile of extra slope on their way to the intersection of the new and old road. So 6 feet, couldn't understand why they were cutting in a fill area. This always works in the PRB was the comment from the construction crews.?ÿ
One of the "interesting" techniques the surveying crews would use was to do a daily calibration; "as a check" before starting. Basically, calibrating on top of an existing calibration. I don't think the machine control crews were doing that, only the mine surveyors.?ÿ
The mapping was based on Geoid 03 and about 8 panel points scattered around the 200 sq miles. The survey checks on the Lidar were amazing. How they did that big of an area that accurately with almost no ground control was eye-opening.?ÿ
Well, there you go. I figured I wasn't the only one.?ÿ
MI-Other-Left, are you calibrating to control county wide?
No, but I don't see why you couldn't if you had reliable data (levels/traverse) for an area like that.
(Remember, it's pretty flat and low in the southern half of the lower peninsula. You get up into the top of the mitten and those folks sometimes refer to us as "flatlanders".)
I've always thought the "county coordinate systems/SPC (from NGS/States)" idea was intriguing. I know some states have that, but I've never worked in a place that uses them.
I'd say that all depends on the project goals and vertical accuracy requirements, as well as how terrestrial work is handled. With proper procedures, RTK/NRTK observations can absolutely be used in lieu of static work.
I second this.?ÿ We've done substantial projects involving miles of road, water, sewer, parks, trails,?ÿ concrete structures of all sorts with contractors that are using machine grading (based on initial site control I set) and there have literally been zero vertical issues.?ÿ We check there data weekly and it's always well within the project tolerances.
I think we know RTK is used the great majority of the time to calibrate to existing control. Some will average RTK observations and some won't if they're in a hurry. Even if I did believe in calibrating, I wouldn't do it using RTK observations. I wouldn't do original project control with RTK observations either. Control -existing or new- requires a solid static survey with the proper number of repeated sessions. This is particularly true in the vertical component.?ÿ
Are we going to talk about surveyors doing CORS/NRTK topo with 1 second shots and 20+ mile vectors? (Because that happens.)
Asking for a friend...
MI-Other-Left, are you calibrating to control county wide?
No, but I don't see why you couldn't if you had reliable data (levels/traverse) for an area like that.
(Remember, it's pretty flat and low in the southern half of the lower peninsula. You get up into the top of the mitten and those folks sometimes refer to us as "flatlanders".)
I've always thought the "county coordinate systems/SPC (from NGS/States)" idea was intriguing. I know some states have that, but I've never worked in a place that uses them.
Got it, I was simply curious. I've seen Geoid contour maps that covered the midwest areas and some of the areas are very benign and some were surprisingly busy (Ohio I think).
If you try to calibrate here it's not pretty for elevations past a small area. A section is way too big, we learned that doing the local small airport, no chance a calibration will work there. Same with the 120 acres that makes up the local college. A lot or a city block, that can work. I'd imagine that if you're in an area with straight parallel evenly spaced geoid contours it would work much better.?ÿ
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Well, I've tried using a network a few different times and so far they have inspired almost zero confidence in my ability to get consistently accurate measurements (especially vertical), so I'll take even RTK over that...
But like others have said I think multiple and/or overlapping static sessions are overkill on certain projects, and yes, even ones where vertical matters.
I shudder at some of the stories I hear about the ways in which others are using their gnss.
There are times when using your gnss is a bit like using your Schonstedt: it's "finesse, feel, and experience". The more time you spend with it in your hands, the better you are at being aware of what it is trying to tell you.
Are we going to talk about surveyors doing CORS/NRTK topo with 1 second shots and 20+ mile vectors? (Because that happens.)
Asking for a friend...
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I've actually done that, works way better than I ever expected. I was on a remote location, base didn't work cause of a power cord and no spare way to get it going. So I surveyed the site with the rover on continuous one second PPK topo to fill in the site with additional topo. Check the two control points and then processed it in the office using the local CORS 50 miles away. Checks were less than 0.1' and all the mixed topo points looked really good. Saved me a long trip back out there.?ÿ
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I've actually done that, works way better than I ever expected.
That's a very unique situation, and that's a good way to salvage the day and save the 2nd trip. (Apparently your site had enough open sky for the gnss to stay fixed during the continuous ppk.)
I've had to resort to that method a couple times too, but I really don't like doing it. Usually it's at the end of the day and the big base battery died (no radio) and I've got about 30 minutes worth of work to complete.
Dial in to the NRTK and away we go. But that's usually just to see that my rover will get a fix. I store those nrtk shots as a last resort rtk value, if needed.
Then I ppk process that 30 minutes worth of work against my gnss base.
@michigan-left very good point. I would add that when I did site calibrations and was holding vertical around the site I would as an extra check throw a fly or even set up a level and get a few verticals in each of the 4 quadrants and middle. I would not tie these as part of the site calibration because tying to a point will always ck within reason. I would after i had completed my site calibration go observe these different points as a check. when we first started doing these i am sure you learned just like me. It almost mimics how we planned gps control for static. Take our project on paper plans etc. roll it our and eyeball about center and make a big cross. Then we would start plotting existing control horizontal and vertical known points where we had none we would set it via traverse or running levels. My mind slips me but we wanted at least a H and V in each quadrant and a V near center if possible. This was all in the planning stage. Making sure to surround our site and not clip any of it as we truly did not want to go outside our baselines. Now this was before a good hybrid geoid model days of course. But similar principles can apply to site calibration when we need to hold more vertical than just the one. One is the best and then check outside points. ?ÿBecause if one held and no cks then a bad point or bad observation can cost ya. ?ÿ
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@norm It still happens. I have seen it the last few years of coming back to the private sector side. I have even seen it done so often that only a really focused brain could keep up with it.
i have seen surveyors try and calibrate to a whole county worth of monuments with lots of vertical change and I don??t understand and all I am told is the same old BS line. That is how we follow the footsteps because everyone around here does it the same way. Which is totally not true. It is a professional working outside their knowledge base and understanding. ?ÿBut I have no way other than being a jerk to say here is the math here are the principles and your wrong. I hate telling anyone they are wrong. But i am just stubborn enough to fight against it to a point then i have to close my mouth and wait and watch knowing the storm is on its way. Try explaining as a non licensed surveyor to a licensed surveyor why he can??t tell a crew to calibrate to every ?ÿpoint along a 5 mile route and hold everything hz and vertical and then go 2 miles perpendicular to that route and call the data good. And the control is all around 300 ft lines traversed by rod only. And i could not make them understand using fast static type methods on some projects would be better than rtk control. To long to much time. To many things can go wrong. Rtk is good enough and we know its good by the rms values. This i have seen and it blows me away. I understand land surveying is not geodetic work and it doesn??t need to be chasing a mm all of the time for a topo or some things. But geezers some of it seems basic logic not to do.?ÿ
...why he can??t tell a crew to calibrate to every ?ÿpoint along a 5 mile route and hold everything hz and vertical and then go 2 miles perpendicular to that route and call the data good.
Forget 5 miles perpendicular, that doesn't even seem to work half the time on an area the size of 1 city block if the control was initially set with RTK. ?????ÿ
@bstrand yep it happens and i have seen heard and been told i was not correct when advising against such practices. Things like it doesn??t matter its all relative etx etc. ?ÿI honestly believe that those folks that ran traverse no gps off ngs monuments on nad27 and did the math long hand where far more prepared for gps and grid coordinates. Even those who did astro shots for azimuth etc. now it??s so easy to turn on push a button and say its right. ?ÿSomehow the knowledge was lost in many ways for today as we can literally push a button. The problem is not understanding what all the breaking points are and what the software is doing. ?ÿ
same on route surveys. Cad is so easy but ask someone what curve definition they are using on a route. Railroad or regular. You will be surprised i am told never heard of anything about different ways or deggree of curves. ?ÿNo one does that anymore its not needed. Thats what I am told. Seems it would be pretty important to know those things even for a boundary along a roadway vs railroad. I have to re learn everything now I guess. ?ÿBecause it seems a lot of what i was taught was way wrong or it doesn??t matter anymore. ?ÿAll i need to ck is rms value and its good. ?ÿ?????ÿ
@bstrand I should have said he should not be telling a crew to do that. Sorry for typo. Should never try and calibrate in a straight line. And hold hz and vertical. And go perpendicular.
@bstrand on a linear project i think holding 1 vertical and 2 horizontal and checking is about as good as anything. So basically translate rotate and using one vertical and hoping and checking the hybrid geoid model in that area. ?ÿ
heck traversing sometimes on linear routes we ran parallel traverse because not a lot of geometry and or strength of figure.
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The problem is not understanding what all the breaking points are and what the software is doing.
Yeah, it was actually kind of frustrating in school because they'd touch on things long enough for one to get a loose understanding of what the software is doing, but not long enough to be able and turn around and explain it to someone else.?ÿ I wish I knew then what I wish I knew now so I could have badgered the instructors for that information.?ÿ It's not impossible to learn things later of course but it sure is less convenient.
I don't think I've ever heard someone call curves railroad or regular.?ÿ heh?ÿ Do you mean spiral or horizontal?
Perhaps on the next project when I set the original 4 control points I??ll run levels and adjust the vertical on them but when I localize I??ll only hold the first one or one that??s set in concrete for vertical. Not sure how it can get much more precise than that. ???
@bstrand look up definition of railroad curve vs highway curve definition. ?ÿ Regular was a very poor choice of word. ?ÿThe degree of a curve is different which results in different values for solving. Radius to chord endpoints etc. Most elementary surveying books or route surveying books has these in them and how to solve.
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I may or may not have had a question in this regard on a test as well ?ÿso much material to cover in a classroom for sure so we have to take that foundation and dive into it on our own . Never ever stop learning it keeps you young ?ÿthats what i tell myself especially when my kids practice counting by using the white hairs in my beard lol. I am sensitive so I run to my room and read when they make fun of me ????. ?ÿI honestly think i study more now as it was for setting the example in front of the kids because they learn more by watching us than us telling them what to do. So as they started doing homework and such and i was debating coming back to land surveying i would just study in front of them as they did . I just hope they become more knowledgeable than I and use that knowledge to become wise.?ÿ
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@bstrand I should have said he should not be telling a crew to do that. Sorry for typo. Should never try and calibrate in a straight line. And hold hz and vertical. And go perpendicular.
This is exactly what happened on a project I worked on about a year and a half ago.?ÿ The project was for a dam in the mountains so of course there was major vertical relief in the canyon and not much room to spread out the control.?ÿ A former employee calibrated in pretty much a straight line to topo some existing buildings and fence line, which did not require elevations.
I rolled out there completely new to the project to shoot some power line sag (which just so happened to be perpendicular to the calibrated control) so a contractor would know where to place cranes, which obviously requires good elevations.?ÿ The office techs got the data and saw a massive tilt which caused a mess for a while...
This was just another reason I hate, hate, hate stepping into ongoing projects.?ÿ You never know what the hell has been going on before you get there...
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