GPS setup along interstate

An Interstate?

Unless you are in an area where DOT only uses VRS, then they should have control set along the Highway. I would get with them and occupy that control with the projection parameters the control is based on.

I would find a good spot with open sky 800-1000feet away from all the action and vibration for the base station. If this is a long project then find several spots and tie them together with your GPS. I use a network rover that gives me NAD83 coords and NAVD88 elevations directly for the base stations but you could use an assumed coordinate (go big) and elevation and then correct up to any DOT control that you find along the way.

If all they want is to replace the CL where it was before grinding it up then just shoot and record the existing painted CL (including pvmt elevations and I would get approximate 25 foot stations) and then use the stakeout program to set stakes back where the paint was with fills to the original pvmt.

Thanks,

The question is more of how to tie the bases together. Collect the CL for about 1000 feet, set a control point at that point, move up the base station and than collect for another 1000 feet and repeat as necessary for the length of the job?l

Theoretically a base/rover RTK setup should be good for around 15 km, radios will be your Achilles heel. If you have access to a repeater radio you could cover 30 km with one base.

If you don't have access to an RTK network solution or know control I would just set up the base at a location favorable to GNSS and out of the construction zone. Collect raw data at the base and start off with an autonomous position. If it turns out you need another base set-up, then set another control point and take a couple of longer RTK observations on it, preferably with 4 hours of separation.

Base with internal radio (or external if you have two) and a high-mast whip antenna, set in a central location with good sky and not in a hole. Running off external battery of course.

Truck with repeater radio running inside the cab, cable out the window to antenna attached to magnetic mount on cab.

Drive along corridor, step out of truck, fire up rover, get to work.

why does it seem like no one else uses RTK over cell? It is just so much easier than having to worry about the radio coverage....

Just did some work today, probably less than 1000 feet from the base but used rtk over cell. No need to worry about radio interference, battery for the radio, etc

And the bandwidth is much bigger, used all four constellations in the woods.

Interstate projects are highly controlled, even a simple overlay. It's difficult to imagine one without site control. I can see not using it causing all kinds of issues, plus with either site monuments or a defined type of DOT VRS it's a no brainer to hook into it.

I suppose that this varies from state to state. I've done a fair amount of DOT work in both Oregon and Oklahoma. Neither state has had reliable control for any project I've been on in the initial topo/boundary resolution stage.

Oregon's DOT maintains a VRN which is used to establish control for their projects. That takes a lot of the challenge out of it. Absent that, I'd establish a string of well monumented base station positions outside of the right of way. Spacing would depend on radio range, up to a maximum of about 20 miles, but likely no further apart than every couple of miles, for convenience. I'd 4 hour OPUS each base and measure duplicate vectors between each in the string, and simultaneously adjust - allowing the OPUS positions to adjust accordingly. I've done this when I've had only internal radios with about ±1/2 mile range, requiring base positions every mile. It works out fine. Set your base on these and RTK your boundary monuments.

why does it seem like no one else uses RTK over cell? It is just so much easier than having to worry about the radio coverage….

That had been my go-to method for years when outside of a reliable NRTK area or I when needed better vertical. Unfortunately, the demise of 3G left me without modem on any of my bases which lack LTE modems or wi-fi. I just need time to figure out a reliable solution for the GS16. I'm thinking a MicroHard Bullet but I need to figure out the cabling.

One reason on not using cell is cell coverage and the other is latency. I don’t mind using cell and have done it both with single base and VRS FKP etc. In rural areas cell coverage gets spotty. In good cell areas certain times of the day usually when kids are getting out of school and the tower can’t handle all the traffic and we get latency which intern can give us suspicious data or less than desirable positions. Years ago when I ran a VRS I had some program I ran under the hood that monitored the latency and such. I have not looked into that lately to see if there is some app or maybe some software’s actually run it. What I have done is run the same r12s head to head with one base right beside the other one running cell me running internal radio. For most of the time testing not a nickel’s difference except around the time buses started trucking kids home and when in canopy that latency caught his gear . But cell is a great option and tool to have in the toolbox for sure especially in areas where you need a bit more distance or a get over some terrain.

If I am understanding the scope correctly. You are just locating center line and that way you can come back and basically put it back where it was before the milled. Being on a datum known coordinate systems is a plus but not necessarily a must in this situation. It’s all relative. I would simply follow @rover83 set a point here position if you have no control for the base in a great open area away from disturbances. Off site set control in both directions of your project. Locate cl re shoot the control move up maybe even paint a dot on cl or make a scribe once moved base to new point to check and keep trucking. You want it all relatively tight so shooting locating a point or two you shot with rover every time you might have to move the base gives you a check nothing went hay wire especially if this is all done in a day. I honestly wouldn’t even worry about an OPUS just set good control every so often that you could reconstruct what you did if you have to come back. The coordinate system and datum are not that relevant except they need to be the same for that work.

Thanks. This is kind of what I have done in the past as needed. keep it simple. Maybe i just over thought it thinking it. I usually question myself as I have had no real survey education. I was given some GPS stuff and told to learn it in two weeks. Crazy how they let the new kid control the job that way. I am always wondering if there is a better way. One of my concerns was if I set a base point at the beginning the further along the job i went, any potential error may increase. Again probably over thinking.

i generally use RTK as the CORS coverage in Maine is not the best and hills and trees don't help. I like to control as many variable as I can.

The area has hills and forest cover that blocks and hinders the signal at times so the distance can be limited.

I have always heard of putting repeaters in trucks. Do you have a picture or description of your in truck setup?

One reason on not using cell is cell coverage and the other is latency. I don’t mind using cell and have done it both with single base and VRS FKP etc. In rural areas cell coverage gets spotty. In good cell areas certain times of the day usually when kids are getting out of school and the tower can’t handle all the traffic and we get latency which intern can give us suspicious data or less than desirable positions.

This has been our experience by and large. That and we would have to get an external modem because the receiver internal modems are all 3.5G. We often see high latency even in large metro areas. Our RTN is full-constellation, and even running RTCM3.2-MSM it's about a 50/50 chance whether we see all four constellations in the solution.

We also work in enough out-of-town areas (at least my office does) that it is almost always easier to just run UHF corrections from the start.

We're a larger firm, and corporate is loath to pay for anything that isn't being used day in, day out.

We use a microhard bullet. I originally bought it because it has a serial port and I was using that with an R7 as a base (which only has serial ports). Now I use it with an Alloy as base, or sometimes R10's. If you get one with wifi then the R10/R12 units can function as a wifi client, whereas the Alloy connects directly to the ethernet port on the modem. If you have a static IP then it is easy to connect directly to the base receiver. If you don't get a static IP then you can run SNIP on a computer in the office and send the corrections there, and then connect to SNIP from the rover.

I recently found a great option...simbase.com. You can get a sim from them that will work pretty much anywhere in the world. They charge $0.01/day for service, which you can enable and disable anytime from a dashboard. Data is charged at $0.01/MB, which comes out to $10/GB if you use it a lot. A public fixed IP is $0.30/day, which is $110/year. I was paying AT&T $56/month for a static IP sim with 5 GB, but I never used anywhere near 5GB, and there were months I didn't use it at all. But I like always having that option active. I switched over to simbase after testing it, and it works fine.

As for latency, I have not noticed it at all, but we almost always are doing static occupations (2 to 3 minutes), not anything kinematic (i.e. moving while collecting like in a vehicle or walking and doing continuous points).

My comments are based on these assumptions and 45 years of experience in route survey:

1) There is no need to replace the centerline vertical component. If this were a requirement the comments would be much different.

2) The horizontal centerline component is being identified by a visual estimation. (eye balling) This means the location may be off a few tenths of a foot or more from where it may actually be based on a centerline survey using centerline control monuments from as built plans. This of course is the proper way to do this which there is no time for as stated. I would have a problem with that if I were approving the work but luckily for you I'm not.

Before RTK the easiest way to preserve estimated centerline location was to simply tape offsets to hubs set out of harms way and pull it back as needed. This would still work in a pinch. This may still be a consideration all things considered. Particularly for an inexperienced RTK user.

To use RTK start in the middle and work out both ways setting control as far from the first base as the radio link will allow. Set your control on hilltops so as to cover the valleys. The first base position coordinate can be assigned or approximate. After additional base points are set and occupied check back to the base point it was set from for your warm fuzzy. Because your centerline locations are estimated to start with your concern for RTK accuracy is a mute point because your estimated locations are well within the tolerances for fixed RTK survey.

With interstate pavement, the centerline seam is vitally important. Usually after the mill there will be a straight side, normally the parking side and the seam is laid out from it simply pulling a tape over. There will probably be two lifts. Those lifts should overlap so the first layout will be maybe a foot past the seam and. The final seam should be packed very tight and the goal is to make the painted centerline on top of it. The idea is to keep as much traffic from running along it since it's the weakest part of the pavement. I'm assuming you were asked to locate the existing seam and then lay it out. One caveat is that design comes into it when there are things like turning lanes. In those situations you may need plan sets for more complicated pavement layout.

the interesting thing is there are two jobs on this interstate separated by 3 miles. It is a 3 lanes, southbound interstate. The engineer on the first job wants to collect the yellow line next to the median as the controlling feature. On the second job, the engineer wants to collect the crown which is between lane 1 and 2, Lane 1 is next to the median. I will probably collect both features just in case. The goal is to collect the information and than will use them to lay out the paving widths with a Tiny MobileRobot. Its great to hear all the answers. They all have information to use.