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Setting up control for construction site

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(@on_point)
Posts: 116
Member Member
Topic starter
 

How do you all set control on a new construction site? Does it make sense to set at least four control points with the total station set up over the 5000,5000,1000 point and then localize the gps/vrs with the control? 

 
Posted : December 7, 2022 6:58 pm
(@gradsmeters-2)
Posts: 18
Member Member
 

Hey, for me it goes something like this.

Internal accuracy of your control points is what matters most when it comes to construction.

Best way to achieve good internal accuracy is to setup total station into middle of the site and let it settle to temperature for 30min or so. Direct sunlight/melting snow under the tripod is bad.

Shoot enough retro targets/prisms/nails as permanent control points. Id say that 4 is usually not enough. Im doing like 5-10 when starting a site.

Make sure that they are fixed into solid places with good unobstructed view that you can allways get back into. Prefer fixed prisms over retro targets if possible. Nails on pavements outside the site is ok too.

Its important to shoot all targets from one station using both faces if possible. More stations and time between shots makes your internal accuracy worse. Check your prism bubble if your shooting points into ground (nails/rebars etc). You can mitigate prism bubble error by turning prism 180 around between shots and shooting the nails twice averaging the result.

The above is the most usual case on normal sites. Usually i free station into the middle of the site with few gps control points and start shooting internal control.

If the site is really big or complex shaped you might have to traverse your points or use GPS and free network adjustment. I dont have experience of that.

External accuracy is secondary. You can be few centimeters off from state grid and its usually ok. It doesnt matter if your whole site is 2cm this way or that way as long as the internal network is tight. Height should be quite accurate because your site connects to surrounding streets. Double check height from known location and dont rely on gps height.

You can measure gps coordinates to few of your control points and tie your internal site grid into state grid. Be carefull not to rescale your internal points when transforming them into state grid with the measured GPS coords as this will destroy your internal accuracy. Only move and turn the points, dont rescale.

 

Internal accuracy = distances and angles between your site control points

External accuracy = your internally tight control point packages relation to state grid coords.

 

 
Posted : December 8, 2022 2:46 am
ncsudirtman reacted
leegreen
(@leegreen)
Posts: 2158
Topcon/Microstation/3DMC Specialists Member
 

Every site is different.  Are you doing site work or BIM such as concrete and steel layout?

I tried to avoid any type of localization or calibration.  It is an adjustment balancing errors. I like to setup a good static GNSS network for site work and tie it to CORS. For BIM projects I preserve the Architects BIM coordinate system and tie this to the static network using LDP.

You will lose control,  just image loosing all four. 

 
Posted : December 8, 2022 4:36 am

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 JPH
(@jph)
Posts: 2230
Member Member
 

No need for GPS, in my opinion, unless it's needed for tying into the site.

Sometimes you need to run a loop, other times just a baseline is needed.  Depends on the situation and site conditions, size, etc.  

Just make sure to set points where they won't get disturbed, cage them up, and also set a couple off-site points, in case everything on-site gets wiped out.

 
Posted : December 8, 2022 4:45 am
MightyMoe
(@mightymoe)
Posts: 9029
Member Supporter
 

Every site we do is projected. No site I've done in a long time was done on site 10,000,10,000 control. This includes construction back to the early 1980's. Long before GPS this was the standard. 

I can't imagine today setting up control for a site using local coordinates. That being said GPS is normally used to set points around the site, levels are run between them and horizontally/vertically they are checked with and if needed slight adjustments with a TS.

I don't think it's going to be much longer that almost no staking for construction will be done.

I'm seeing it now in our backwater location. The last subdivision we set control up for this fall was complete machine control construction (except maybe for sewer, not sure, we weren't around for it). But all the over grading, streets, curb and gutter, walks were all machine control. We gave them our control and they built it.

The surveying company involved didn't stake much of anything beyond some fill in points for a robot that controlled the machines. I'm also seeing it next to the office where a bank is being constructed. Haven't seen any surveyors there at all, they do have a permanent tripod set over one of our control points. Taking construction staking away from surveyors is going to happen,,,,,,,,and soon. 

 
Posted : December 8, 2022 5:44 am
jflamm
(@jflamm)
Posts: 225
Member Member
 

Posted by: @gradsmeters-2

External accuracy is secondary. You can be few centimeters off from state grid and its usually ok. It doesnt matter if your whole site is 2cm this way or that way as long as the internal network is tight. Height should be quite accurate because your site connects to surrounding streets. Double check height from known location and dont rely on gps height.

You can measure gps coordinates to few of your control points and tie your internal site grid into state grid. Be carefull not to rescale your internal points when transforming them into state grid with the measured GPS coords as this will destroy your internal accuracy. Only move and turn the points, dont rescale.

 

Internal accuracy = distances and angles between your site control points

External accuracy = your internally tight control point packages relation to state grid coords.

 

 

With all due respect, this is why the PLS needs to have oversight over construction layout persons.

Maintaining the relationship to the boundary and the original control point network used for the boundary is the most important thing. Being tight to state grid coords really doesn't mean anything. It's the relationship to the boundary and R/W's that have gotten distorted since you're now on 2nd, 3rd or 4th generation control from the original boundary traverse control network.  I'd be more worried about laying anything out over building lines, easements, right-of-ways and boundary lines before I cared about how I checked into State Plane.   

 

 
Posted : December 8, 2022 6:09 am

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(@bstrand)
Posts: 1665
Mapper of Things Member
 

Many of the projects I work on are on the smaller side-- pedestrian ramp rebuilds, lift stations, etc.  I try to set 4 control points.  I don't typically level through them since the staking surveyor will probably just localize and hold one of them for elevation anyway.

 
Posted : December 8, 2022 6:32 am
 JPH
(@jph)
Posts: 2230
Member Member
 

@mightymoe 

I guess it depends on what kind of construction site.  If it's a building, no site work, then I'd have no use for GPS/SPC.  Especially on some of the sites I've done, an addition on an existing building, which is basically your starting control

 
Posted : December 8, 2022 10:17 am
Rover83 reacted
not my real name
(@not-my-real-name)
Posts: 843
Member Member
 

It depends on what you are constructing. In most construction I have participated in greed and power were the motivation for the owners. It was difficult to do things properly. I met a lot of people who had more money than brains, and a lot that were just plain stupid. The one thing they had in common was that they were bull-headed, and always thought that bossing people around would get things done correctly.

 
Posted : December 8, 2022 11:13 am

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(@wa-id-surveyor)
Posts: 787
Member Member
 

If your setting new control on a construction site the first thing you need to do is tie into the existing project control.  The means and methods will be dictated by the location of the existing control. After that, you determine the method that is most efficient for the project while maintaining the required project accuracies.  There is no standard way, each project is different.  

 
Posted : December 8, 2022 12:18 pm
Brad Ott and jflamm reacted
MightyMoe
(@mightymoe)
Posts: 9029
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Posted by: @jph

@mightymoe 

I guess it depends on what kind of construction site.  If it's a building, no site work, then I'd have no use for GPS/SPC.  Especially on some of the sites I've done, an addition on an existing building, which is basically your starting control

I know what you're saying.

But everything I do is projected, highways, bridges, reservoirs, coal mines, oil and gas, no matter the size, subdivisions, house layouts, all of it. 

Start doing it and you won't regret it. 

 

 
Posted : December 8, 2022 3:32 pm
(@on_point)
Posts: 116
Member Member
Topic starter
 

Wouldn’t you still have to scale your SPC’s other wise your gps and edm measurements would be off? Also, I was under the impression you were better off with site coordinates that look nothing like State plane to avoid any future confusion?

 
Posted : December 8, 2022 6:12 pm

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Samlucy3874
(@samlucy3874)
Posts: 63
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Crank 4 sets D & R. within a box that kinda mimics site. do it trig levels, then run good optical levels. and tomorrow as new things occur do those again. worth the time and people are watching your procedural things. 

since 1985, only 1 bust because of h.r.

 
Posted : December 8, 2022 9:59 pm
MightyMoe
(@mightymoe)
Posts: 9029
Member Supporter
 

Posted by: @on_point

Wouldn’t you still have to scale your SPC’s other wise your gps and edm measurements would be off? Also, I was under the impression you were better off with site coordinates that look nothing like State plane to avoid any future confusion?

No, if you wish to work in SPC, there's no reason you can't with modern equipment. The DC will calculate everything correctly. Of course, you need to understand the equipment and how the software works. 

I don't work with SPC coordinates but if you want to you can, we use projections that closely approach ground distances, I like to keep the ground/grid error under 10ppm.

The DOT procedure is to multiply the coordinates by the project scale factor. Since they placed control all over the state starting in the 1960's we generally used those monuments for our geographic control along with NGS monuments that are scattered through the region. This has allowed us to have extensive interconnected networks of coordinates wherever we go. Long before GPS/CORS/OPUS. But now with all that available why not use it. 

As an example, I have a small job in a town some distance away that I haven't worked in. Done lots of work surrounding it but not in town. I was able to get a control sheet from DOT and occupied one of their points in town and now I'm on that control. This is good cause an engineering company is doing a water project through the main street and they are using the same control. There are lots of found monuments on a couple of ROS's using the same control network. It's all interconnected. 

If it's some small lot survey we occupy control that we have spread about our town, if we don't have control it's a few minutes to set control with the R10 then occupy it with the robot,,,,,why not? All those survey monuments get put into a city control drawing and anywhere there's a new project we usually are able to calculate within tenths search points for monuments. 

A quick screen capture of a city drawing. 

All the points are on the same projection. 

We have similar drawings for other towns and areas. 

 

 
Posted : December 9, 2022 6:37 am
Brad Ott reacted
 JPH
(@jph)
Posts: 2230
Member Member
 

@mightymoe 

I use GPS on many jobs, even when I don't think it's needed.  Sometimes it makes solo recon for remote points a bit easier

 
Posted : December 9, 2022 6:51 am

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