What happens to your positions when someone measures the rtk base station height wrong but the rover is correct. Also you move the base to another point and height is still wrong and rover is still correct. ?ÿDo you just say I don??t care about vertical and only horizontal. ?ÿ
Things to remember is 3 dimensional. The earth is not flat.?ÿ
The way RTK works in the trimble world is that the vector is stored in the data collector as antenna phase center (APC) to antenna phase center. The HI's that are in the file are applied to display mark-to-mark vector components. So, if you are using TBC then you can just change the incorrect HI(s) and re-compute. I don't process RTK vectors in TBC, I use software that I wrote, and in the database created I store both APC-to-APC and mark-to-mark. It won't affect the horizontal.
I have argued with knowledgeable people in the past that if I just want 2D then it does not matter. Never got them to see it that way, though.?ÿ
I don't know about other data collection systems, though
?ÿ
?ÿ
?ÿ
?ÿ
I agree with mark to mark or APC to APC. But disagree on horizontal only as the height will change the reduced horizontal distance. The lines vectors are not parallel. ?ÿ
Think of it kinda like an old theodolite with too mount edm. You adjust the edm the correct way to hit center of prism as your cross hairs aim below center of prism. Now the vertical line and edm distance are parallel. Correct slope distance can be reduced correctly. Now I had a guy bind one and adjust the edm to shoot center of prism while aiming center of prism. At certain distances and elevation change not much not a big deal but lots of vertical relief and it shows up quickly.?ÿ
[Me running a field training class]
Repeat after me:
"There's no such thing as a 2D GNSS measurement"
"There's no such thing as a 2D GNSS measurement"
"There's no such thing as a 2D GNSS measurement"
-----
We often process and adjust mixed data (static, RTK, and terrestrial) from multiple days' worth of observations. I can't process anything - 2D or 3D - if we're just throwing up a base every day and not noting its height. No way to get a good network solution with that kind of data.
That being said, I agree with @john-hamilton, it's certainly possible to perform a 2D GNSS survey. We tend to not like to acknowledge this because the next thing we know, a crew will go out and do a boundary + topo, forgetting that only the boundary needs to be 2D, and not even bothering to plug in base OR rover heights.
I don't know about other data collection systems, though
I think this is the critical piece here. Trimble is handy in that it is possible to post-process and change the measurement location as well as HI. I'm not going to say I haven't "backed in" the base height using common rover points from a good session and processing both the good and bad sessions with zero-height APC-to-APC vectors to figure out the difference....
...but it's just janky to me, and won't pass internal or external QA/QC standards for most of our clients.
It's just too easy to get that measure-up.
I'm guessing the horizontal will be off by the error in base height times the sine of the difference in latitude or longitude (or a combination thereof), which is probably negligible for you.?ÿ
My reasoning is that the computation has to move from the rover APC down to the ground point, moving along the normal to the ellipsoid.?ÿ Since the normal is not the same at base and rover there is a tiny horizontal error caused by moving the wrong amount vertically.
That heuristic model would say that if you had set 0 on the base but put it on a 2 meter pole, and were 0.1 degree away in lat or lon (~10 km) it would make 3.5 mm horizontal error.?ÿ As I said, probably negligible for most jobs.
I routinely submit .t02 to centerpoint RTX post processor with incorrect HI's. It is easy to compute corrected ECEF XYZ coordinates for the mark by using the following formulas...
MARK-X = OLD X + Cos(latitude) * Cos(longitude) * deltaH
MARK-Y = OLD Y + Cos(latitude) * Sin(longitude) * deltaH
MARK-Z = OLD Z+ Sin(latitude) * deltaH
where deltaH=processedHI-actualARPHI
At typical antenna heights there is no change in position
@olemanriver Computations are not done using horizontal measurements. They are done using ECEF XYZ and DX DY DZ vector components. I stand by my statement that at typical HI's there is no effect on the horizontal position.?ÿ
I am of course not advocating a 2d adjustment, nor even saying it is possible. But what I am saying is that if HI's are neglected or wrong, the horizontal should still be good. Depending on what LSQ package is used, it may show large residuals in all three components. Some packages do the adjustment in ECEF XYZ, others convert the ECEF XYZ to NEUp and can therefore isolate the HI blunders
The processing is sensitive to inaccuracies in the starting coordinates, if I recall off the top of my head it is 1 ppm per 6 m error in starting coordinates. I always seed my processing with accurate ITRF14 coordinates, but that is probably overkill. Autonomous pseudorange positioning nowadays is typically accurate to better than 2 meters, so that is hardly an issue. But it can be it there is an incorrect position in the rinex header, for example.?ÿ?ÿ
?ÿ
I have seen observations done by non-surveyors where they didn't record any HI's. They were trying to get azimuth to orient and test large radar arrays. Height did not matter. I was able to give them good azimuth and (horizontal) distances
?ÿ
Actually, I recall that there was a research paper done by Tom Meyer that addressed this issue.
?ÿ
Edit: found it...
?ÿ
https://opencommons.uconn.edu/cgi/viewcontent.cgi?article=1003&context=thmeyer_articles
The possible errors he found were for extremely long baselines, which does make sense. But for typical length lines it is negligible
You really don't need to wonder. Do it and you'll be surprised.?ÿ
@john-hamilton yes sir I understand that its not horizontal for sure and I truly hope I was not coming across as bucking you. I was hypothetically asking and the edm top mount was Kinda like.?ÿ
Here is the true issue I discovered and I knew something was written and was told it was not. But was able to confirm it today.?ÿ
base station set up logging data 0.5 ft antenna bust. Sent to opus with wrong antenna. Update base coordinates recompute rtk vectors. ?ÿSet up on other end of project same thing collect logging data at base while doing rtk tie points in middle of site from each base. Both bases had incorrect height rover rod was correct. ?ÿMove base to one of the rover positions. Base still wrong tie to some of the same points again do other rtk work. No one ever caught the issue in field .
?ÿ
me ask questions how did you set up a fixed height tripod and not have an extension so base radio antenna could stay on. No way base is 2m to arp. Yes it can i was told. Well I discovered i was right. So i get to go edit and fix everything including traverse data as the adjustment and everything pointed to what I thought but no one believed it happened.?ÿ
second project is over 20 miles long. Same issue all along the whole project. Now we all agree if we are going to do a LSA along this route we might need to fix the height issue.?ÿ
that paper is a good one. Read it a while back. ?ÿAnd again not bucking you at all. Just throwing it out to get the wheels turning.?ÿ
because my LS after i showed him this said man i was assuming they were doing it correctly. He was in the field and missed this. He assumed that 2m was 2m was 2m. He is no slouch. ?ÿBut when crews are told its a 2m rod make sure they know that is tip to top. And may not be to ARP or any other item in between. ?ÿIf his crews misunderstand and he made the assumption then their are others. Also i have caught in the field someone accidentally placing the pin in the fixed height tripods that are not truly fixed place the pins at 1.9 or 1.8 or whatever instead of the 2m spot. I teach a quick picture of bottom of rod and picture of top so i can see which adapter is on top. Some of the gps tripods are truly fixed some are adjustable and often after getting beat up hang up at the bottom sometimes.?ÿ
John I sure hope i didn??t come across as rude. I respect and learn a lot from your comments. And all the others here. We all learn together.?ÿ
@rover83 So I met my LS today to get some equipment and showed all the ways things can go wrong on some equipment and now I have to teach a class. I love your Quote. What is bad is I have told others that when the see the vertical precision go sky high but hz is good enough to be very careful because something is going on and your horizontal may not be as good as you think it is. I use the vertical a lot in canopy to be a extra little indicator of what I am trying to achieve horizontal ?ÿnot always but it can indicate a bad fix quicker than the hz precisions. Especially when you look at the azimuth and elevation of the satellites and understanding of what??s around you. I might have to send you royalties on that quote.
me ask questions how did you set up a fixed height tripod and not have an extension so base radio antenna could stay on. No way base is 2m to arp. Yes it can i was told. Well I discovered i was right.
It's still surprising to me how many crews just turn their brains off during what is arguably the most critical part of the day - making sure that the ONLY reference point for ALL the day's measurements is 100% correct.
We found some crews putting the 0.15 meter lever arm extension on the 2 meter fixed heights for simple static observations (no UHF antenna on the unit), and calling their measure-up 2 meters - to the ARP and not the bottom of QR. So not only did they have the incorrect height, but would have had the wrong reference point too.
Seems that they thought because they used the lever arm extension with traditional tripods on other static work, they needed to use it with the fixed heights too. And because it was a fixed height, they needed to record "ARP" instead of BQR. Ugh. No reason for it other than "that's what we thought we needed to do".
?ÿ
On a lighter note, I couldn't stop laughing when I recently watched a crew set up a receiver on an unknown point and, before starting the RTK base, stand there for five minutes straight tapping the "Here" position in order to "get the best position" before starting work. I didn't know how to begin to explain that one so I shrugged my shoulders, it was only five minutes and didn't hurt anything.
There is a LOT of misinformation and misconception floating around, and bad info travels faster than good.
@rover83 The extention lever is exactly what bit the crews for me. It is 0.49 ft and they typed in data collector 2.05 meters. Why i have no idea. ?ÿNow I am one usually that takes full blame for anything a field crew or field members under my care do. I am not licensed but if someone places me in charge then it is my fault even if one of my folks just mess up. I try and figure out a way for that not to happen again. Hence the i want a picture thing. But this work was all done before I was hired and i am still new so i have the whole learn how they do things first and don??t rock the boat. But I had to make the call to two different PLS folks today and explain. Was not fun. Not to mention this job my direct LS again before i hired on. Did some crazy stuff making stuff work and I been sifting through it all slowly plus learning TBC more. From you and others. It just proves to me how having good field procedures just about eliminates the craziness. Like point naming. Keeping everything on grid so your not mixing and matching data.?ÿ
Taping in the here position huh. LOL. ?ÿI love it. I almost went full blown USMC today as my boss said hey get the base and rover from that crew so we can have it next week. I said he has no base and rover just rover. Boss said well he is supposed to have one. I ask the crew chief he said they took that from me a month ago because I don??t need it on this job. I am new here remember. I am like telling my boss nothing is getting done until i have a complete sn# list of everything and i can have every crew chief do an inspection and inventory and with pictures. The. When we are planning i know who has what. In the USMC we called this junk on the bunk inspection or poncho inspection.
I deployed folks all o er the world with Trimble 4000ssi msgrs units and all the freaking cables and never once had someone leave without something they needed. Now did they come back with everything nope but they had everything on my watch leaving. We would have to dummy chord canteens to folks so they would not lose them. Dummy chord is parachute chord tied to whatever and the person. ?ÿ ?ÿ
On a lighter note, I couldn't stop laughing when I recently watched a crew set up a receiver on an unknown point and, before starting the RTK base, stand there for five minutes straight tapping the "Here" position in order to "get the best position" before starting work.
SMH.
My concern there would be if they know to not do the "here" position if they have to extend control on a project.?ÿ Given some measurements reported, I'm almost positive a colleague followed someone that did just that.?ÿ It appeared to be a few clusters of points based on "here" positioning with bearings matching within RTK expectations, but offset by a few feet in different directions.
@john-hamilton oh I also have not heard anyone except myself lately use the term seed my position. You do go back when S/A was still active and trying to use gps to tie in HARN control that not always met what we thought it should meet.?ÿ
It is absolutely amazing besides my favorite which is retracing boundary surveys especially the old ones like done in chains but measuring to between in whatever form levels etc and seeing just how well things were done with almost no electronic equipment. I have been blessed to do this in the good ole USA and other parts of the world. One thing that I have learned is tgat it takes discipline to do good work and pay attention to details. Look at the history of NGS and all the level runs all across the country. ?ÿYes some have moved some maybe were blundered or pencil whipped humans and maybe a bad hangover. But for the most part truly amazing work done. I for fun and a okd digital transit turned to some old azimuth marks smoke stacks basically from an old 1934 fond monument and played around digging through the ngs data sheets around the Dahlgren VA area a few years back. This was a Home Depot type piece of equipment. But I was well within tolerances with what I had to work with wrapping a few angles to another mark. ?ÿI always wanted to do static around those and re observe with good equipment to see just how close i could come to published. Lots of great surveyors that did work without a button to push. Now we can almost be sloppy and still get a decent answer. I mean the robots compensators are so good it is amazing. I use to check zeros several times a day as a I man and re level and check centering. Now I still do but it??s usually so tight I don??t have to worry. Years ago it was much more crucial. ?ÿEspecially if you were on a point for several hours. ?ÿ
I don't know about other data collection systems, though
When the Javad Triumph-LS first came out there was no way to correct the exported RTK vectors for a bungled base/rod height.?ÿ At my request the design team fixed that, which has saved my bacon more than once since then.
which has saved my bacon
I thought they did (or were trying) to get rid of bacon in CA?
Either way, keep an eye on your bacon!
This thread is a nice reminder to check your equipment and verify that it can record rtk vectors, and why it's important to use vectors instead of just coordinates.
And check your HI. And check your ARP. And check your level bubble. And check your antenna make/model. And check...
And verify you brought the: data collector, job folder, extra receiver batteries, all the rover parts/pieces, a lunch, 9v batteries, put the fuel lid back on the vehicle, dry clothes, bug dope, extra boot laces, a slide rule for the old guy on the crew, ephemeris tables, more than one handheld radio, turkey baster, fishing pole, camera, pins & caps, tire chains, pencil lead, coffee, iPhone, iPhone charger, iPhone cable, iPhone case, iPhone 12v cigarette lighter charger, iPad (in case you lean that way), mobile hotspot, RTK bridge, laptop, and on, and on, and on...
@michigan-left Check check and recheck for sure. And ASSUME nothing. ?ÿAll you all PLS surveyors that have years of knowledge and experience make a list of the little things because your crews just might be not doing what you think or assume. When my LS allowed me to show him a few issues with fixed height tripods for gps that are not always fixed but can be multiple heights was like I knew that but didn??t remember that until I physically showed him also things like gitney as what i call the brasa insert where antenna sets in can get stuck and not seet all the way in. Now that??s usually not much but its going to be aware of it. Besides GPS things like -30 and 0 offset prisms not being put on correctly or missmatched because crew is scared to ask for a new one. Some of the old topcon prisms do not screw in all the way to a seco -30 and 0 offset prism. Not much a few mm but it is an issue.
I routinely submit .t02 to centerpoint RTX post processor with incorrect HI's.
Isnt' that kinda hard to do unless it's just a static file?
Base/rover would have the HI, and Fast Static/Static allows you to enter an HI.
Unless you're one of these Trimble 4000 aficionados? (Which still allowed an antenna height input, if memory serves.)
?ÿ
I have argued with knowledgeable people in the past that if I just want 2D then it does not matter. Never got them to see it that way, though.?ÿ
That being said, I agree with @john-hamilton, it's certainly possible to perform a 2D GNSS survey. We tend to not like to acknowledge this because
(*CRINGE*) This sounds so naughty and it makes me feel dirty, like I need a shower.
I know that you both know what you're talking about, but some people don't and may not understand the principles you're referring to.
Favorite line in this thread:
[Me running a field training class]
Repeat after me:
"There's no such thing as a 2D GNSS measurement"
"There's no such thing as a 2D GNSS measurement"
"There's no such thing as a 2D GNSS measurement"
This one time (at band camp) I had to spend the better part of an hour explaining that GNSS does not directly measure ortho heights between marks, to a 30-year surveying veteran.
Even after all the explanation, he was not convinced, and said he'd look into it and get back to me.
I have processed a LOT of data over the last 36 years, and for a lot of different users. The stories I could tell...