I did not want to hi-jack the prior posts concerning RTK and its uses (or misuse).
I have also been using GPS for quite a while and started with Post Processing everything with static observations and OPUS comparisons.
Since we have been using network RTK we rarely post process any longer since we typically have very good results with the RTK as compared to static. Often we will tie into a close geodetic monument when we can and typically we are under a tenth in both position and elevation, often much better.
Most of our use is setting 3-4 points for boundary and topo surveys around the perimeter and tying into those points conventionally.
Our process is to collect each point for 45 seconds, twice in the morning and then again twice in the afternoon and let the software weight and average the points. Using this method we typically tie into our RTK points within hundredths when comparing conventional to RTK.
Interestingly in the weighted average sometimes the checks within the same points are hundredths, sometimes a tenth or a bit more.
With enough redundancy and averaging though they almost always check to our ground control very well.
This goes along with the prior statements that when used correctly they are a great tool. We have been doing less and less conventional traversing since we use the RTK points as our closing and check points.
So, I am curious of a couple things. One, how many people are using RTK for stakeout work and two, when doing so is it with a network solution or a base and rover solution?
We will certainly use it for stakeout but only for rough grading. Many think I am crazy for not using it for curbs, inlets, manholes etc...
I personally am not comfortable enough in the differences in elevations (and the once in a while outlier point) to use it for these items and we either use a robotic or conventional instrument. Many items we are staking these days have pretty minimal slopes and grade changes so I would rather have the confidence that it is checked properly.
I can definitely appreciate the ease of use and the idea of not having to set up an instrument all the time. It obviously helps when there limitations on line of site as well.
Curious what others do and/or your opinions.
Thanks
We use it almost exclusively for layout, off of both base and networked gps (depending on how far out of town we are, away from the network base). We let the contractors know which elevations are gps, though- we will mark up water line with gps elevations, but not anything with a gravity flow- it just isnt close enough.
All of our curb layout is done with gps, but graded with a level- it ends up being the fastest way (for us) to do it, as horizontal is not nearly as critical in curb layout. I've seen a lot of curb graded with gps, and it never seems to look right on the string line.
Mark Davis, post: 365753, member: 9317 wrote: We use it almost exclusively for layout, off of both base and networked gps (depending on how far out of town we are, away from the network base). We let the contractors know which elevations are gps, though- we will mark up water line with gps elevations, but not anything with a gravity flow- it just isnt close enough.
All of our curb layout is done with gps, but graded with a level- it ends up being the fastest way (for us) to do it, as horizontal is not nearly as critical in curb layout. I've seen a lot of curb graded with gps, and it never seems to look right on the string line.
Thanks Mark - I have thought about using that method with the level as well.
I have also seen guys staking foundations with it - that's not for me
We have no use for GPS here. Sounds funny I know but it's true. No open areas and no large jobs.
We only use it for elevations for elevation certs. I've checked many times into USCG benchmarks and it is spot on +/- 0.1' usually but most of the time closer.
I've only used it a few times for horizontal and that was to tie one set of control to another on the next street so I didn't have to traverse through a jungle/swamp. How close was it? Close enough. Call me what you want but I wasn't looking for 0.001 agreement. I shot a prism less house corner from one to the other and was within 0.1' good enough for what I was doing.
I personally wouldn't use RTK for high precision work.
We use GPS, both VRS & Base corrections for staking mass grading, overlot, foundation sub-ex, water pipe and general checks. Anything relating to fine graded elements especially parking lot curb, sidewalk, foundations & gravity pipe is all done with a robot. With the ADA slope requirements I don't feel like GPS is good enough when the designs are always bumping into the max/min slope limits. I would consider using it for street work so long the longitudinal slopes were in excess of 5% and the distances were long enough to see an increase in production speed using GPS over a robot.
I've started using GPS for foundation layout but only on stick frame architecture which for me is almost exclusively residential. Anything commercial or industrial or with structural steel is always done with glass.
Generally I run 1-person crews for construction staking so the GPS/level model isn't an option.
Cheers :hi5:
I run network GPS and robotics like you. I might stake a footing with GPS if I was going to go back and pin it. I think I have done that before, but I always pinned it with the robot.
I just staked a ton of curb today, and I did not use the GPS at all. I did the whole thing with the robot. Like you said, the 0.1' up and down could really screw up your curb layout.....same with sanitary and storm inverts. There are too many cases where the fluctuation in elevation measurements is too extreme to reliably layout those utilities.
Here are the rules for road setout in Western Australia:
It is the responsibility of the contract surveyor to determine and undertake all construction pegging requirements. This section has therefore been included as a guide only based on past MRWA practice.
RTK GPS complies with vertical accuracy to Sub-Grade only. It is not to be used for vertical set out on base course final level or for structural set out (vertical or horizontal).
RTK GPS provides an acceptable accuracy for horizontal set out of all sub grade, sub base and base course pegging.
Gregg Gaffney, post: 365755, member: 1111 wrote: Thanks Mark - I have thought about using that method with the level as well.
I have also seen guys staking foundations with it - that's not for me
I staked a few foundations with rtk. I set hubs without tacks at every corner, then chose a good long line to set two tacks. Check the distance with a tape, adjust and let the form guys do the rest.
Yes, I had feet to the the setback and the client wanted it cheap. The foundations came out within the usual 0.05' I am used to seeing.
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Cameron Watson PLS, post: 365758, member: 11407 wrote: We use GPS, both VRS & Base corrections for staking mass grading, overlot, foundation sub-ex, water pipe and general checks. Anything relating to fine graded elements especially parking lot curb, sidewalk, foundations & gravity pipe is all done with a robot. With the ADA slope requirements I don't feel like GPS is good enough when the designs are always bumping into the max/min slope limits. I would consider using it for street work so long the longitudinal slopes were in excess of 5% and the distances were long enough to see an increase in production speed using GPS over a robot.
I've started using GPS for foundation layout but only on stick frame architecture which for me is almost exclusively residential. Anything commercial or industrial or with structural steel is always done with glass.
Generally I run 1-person crews for construction staking so the GPS/level model isn't an option.
Cheers :hi5:
I was thinking the same thing about the slope of the roads. With enough slope in there you would never see the minor errors, the large ones should jump out easily enough. Of course most of what we stake is relatively flat
Thanks guys - sounds like we are all on the same page.
I have a new guy starting soon and he was a bit shocked that we don't stake most items with RTK.
Always good to have someone challenge your thought process a bit so you can examine other methods.
Gregg. I have one employee who I turn loose with robot, I use GPS. I check into one of his stakes about every few minutes and adjust to match the robot elevation. This goes real quick and keeps your elevations tighter. My .02
We use network GPS quiet a bit but never for anything that needs a great deal of accuracy. For the most part we use it to establish grid on jobs that need to be tied to state plain coordinates. Other wise it gets used for doing topo work or shooting parking lots on large jobs. I don't think i have located more than 2 or 3 actual property corners using GPS and those were done because it would take all day to traverse to one corner.
I saw a former coworker one day, who now is a high up engineer in a large construction company. We got to talking about GPS and he said a salesman came by telling how good it was. He said, "It's accurate down to a quarter of an inch". My friend asked, "Can I lay out a bridge with it." The response? "Brother, I don't think I'd do that."
We use Topcon GR-5's for RTK stakeout (Base and Rover solution). It has performed well for horizontal stakeout but i wouldn't recommend it for vertical/elevations for anything more than TOPO's or other non-critical elevation tasks.
Today we experienced something strange: Has anyone else experienced dissimilar readings depending on which way the user is oriented while performing a point stakeout? ie: stake a point facing north, and then pivot the rod and stake the same point facing south. I was under the impression that it shouldn't matter what orientation the user was facing with a base and rover, but we're getting as much a 4 inches difference between north oriented stakeout vs south on the same point.
I use GPS for layout and rough grading also, but not usually for curb or paving stakes or foundations. The exception might be if the pavement had a lot fall and grades were not that critical. I will layout the pavement and curb with the GPS but then come back and set grade with a level. We use a base and rover setup.
