Checking control

If it's control, why would you want to "skin" it?

What are the control points?
How large is the site?
What is the datum?
Do you have access to any of the notes and calculations for the control as it was established?
Do you know what if any adjustment was used on the control network or traverse?
What are you going to use the control for?

I NEVER "automatically" trust anything, especially [so called] "Control."

Just because there are 3 or 4 (or whatever) "Control Points" out in a given area, doesn't make them "golden" (even if they have been used several times since being originally set/positioned).

I would CHECK each and every one using the same procedures/techniques that I would use to establish NEW Control for THAT particular Project.

If (maybe big IF) one or more of them has "moved" relative to the others, OR the whole bunch of them stink, then I would want to know that going in, NOT AFTER I had done a bunch of work ASSUMING that they were solid (spatially and otherwise).

Loyal

I don't know if I'd always go so far as Loyal does, but I might. It depends on what was being done with the control, how much I knew about how the control was established, and the quality of the monuments, etc.

If the monuments were of a type that were likely very stable, and I knew that the original work was well documented and of high quality, and I could set up somewhere in the middle where I could see all 4 points, I might just do that.

Rankin_File, post: 444897, member: 101 wrote: What are the control points?
How large is the site?
What is the datum?
Do you have access to any of the notes and calculations for the control as it was established?
Do you know what if any adjustment was used on the control network or traverse?
What are you going to use the control for?

The control points are punched 3" aluminum discs set in concrete.
I have no idea how stable they are yet. The site is roughly 500'x500'.
No access to notes or calc. I've just been given the grading plans with benchmark info. The original survey was done back in '89.
I'm laying out piers and cable trays in a gas compressor site, and performing an as-built survey of the existing equipment and buildings. Tolerances around .03' for the cable trays and piers.

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I would occupy all 4 points and record 8 sights. I would do all location from my current work and adjust my work if necessary back in the office. Then I would compare my work to the prior work. Given the original date of the control, I would not be particularly inclined to adjust it into my work and would most likely do a best fit of my work to the previous and call it done.

Paul in PA

Will the infrastructure you are laying out need to match existing features or will it all be new build? If existing features are there and will need to be matched into you may need to verify those features are in the correct location otherwise the control may not matter. If it's new build then the control just needs to match itself....

I would sit on each station and traverse through all of them, then if possible tie them in diagonally. Then go back to the office and Starnet it to figure out the residuals of the stations.

I found some old traverse control points from the 1950s, I was surprised how good they checked. On another project I found some 16s (not a typo) set around 1990, at least they are sub-tenth. 16s, now that is really old school.

Agreement with Loyal!

The amount of time, effort and money that can be wasted because of a defective position for just one control point is incaluculable until after the fact. The control is to be considered "all bad" until proven correct.

How, if the situation occurs, will you explain to your client that there was a bad control point - that you didn't check?

Man you guys are over killing it for goodness sake. Check the control....of course but you don't have to reinvent the wheel.

I've laid out thousands of piers and even more anchor bolts for everything from the cable trays you mentioned to huge piers supporting steel going hundreds of feet in the air.
There are a couple of things you have to remember when laying our piers.
Don't zig zag the darned piers, keep them straight.
Know your tolerances. Your base plates usually have 1/8" tolerance all the way around, so between two baseplate you may have an allowable 1/4" of wiggle room.
Tolerances add up.....so know where you are tying in. If it is a hard tie in point (existing structure) don't let those 1/4" tolerances sneak up on you.
Keep the lines straight. Nothing worse than zig zagging piers! Albeit 1/4" at a time but still crooked is not good.

Depending in the load many piers for cable trays are sonotube and only about 4 feet deep. Easy cheesy.

arctan(x), post: 444910, member: 6795 wrote: The control points are punched 3" aluminum discs set in concrete.
I have no idea how stable they are yet. The site is roughly 500'x500'.
No access to notes or calc. I've just been given the grading plans with benchmark info. The original survey was done back in '89.
I'm laying out piers and cable trays in a gas compressor site, and performing an as-built survey of the existing equipment and buildings. Tolerances around .03' for the cable trays and piers.

Sent from my SAMSUNG-SM-N920A using Tapatalk

500' x 500'. Verify the control as part of the as-built. Know what is being used. Can't be but a couple of hours worth of work. Sleep well at night knowing all is well.

I'd check the control. An airport job we did they supplied us with the control. We knew the Surveyor who had done the control and didn't trust his work. After checking his control one point was .45 feet off and the NGS control cap he gave us his coordinates on was 35 feet off. He had given us an Azimuth reference cap and thought it was the NGS control station. Obviously we would relied on that point to be the most accurately. Don't even trust yourself check your control.

Skeeter1996, post: 444936, member: 9224 wrote: 35 feet off. He had given us an Azimuth reference cap and thought it was the NGS control station

Pedantic post here: in NGS data sheet terminology, at that distance it would have to be a Reference Mark and not an Az mark.

Bill93, post: 445034, member: 87 wrote: Pedantic post here: in NGS data sheet terminology, at that distance it would have to be a Reference Mark and not an Az mark.

You are correct it was a Reference Mark.

As surveyor_a and Just A. Surveyor said, it's more important to be true to the existing structures, utilities, and equipment on the site. So, go ahead and check into the existing control points, but also shoot whatever your new stuff is tying into.

If the 4 points are only 500 ft apart, you could traverse/triangulate around it, starnet, minimally constrained. Then apply existing control values tight, best-fit, not fixed.

You could that faster than not.

JPH, post: 445110, member: 6636 wrote: As surveyor_a and Just A. Surveyor said, it's more important to be true to the existing structures, utilities, and equipment on the site.

arctan(x), post: 444910, member: 6795 wrote: Tolerances around .03' for the cable trays and piers.

With respect to nearby structure...

It's unlikely anyone cares whether they are within this tolerance from a point hundreds of ft away, so long as everything fits together.

It seems unlikely the old control was established, transferred to structures built from it, and remained stable all to that tolerance.

Larry Scott, post: 445130, member: 8766 wrote: If the 4 points are only 500 ft apart, you could traverse/triangulate around it, starnet, minimally constrained. Then apply existing control values tight, best-fit, not fixed.

Commonly I get control from the topographic/boundary survey phase of a project, by others, to use for the construction layout. And just as commonly that control consists of nothing more than Mag Nails in the asphalt and sidewalk cracks reported only as points in a CAD drawing file. Naturally, the control is just where it will be the first thing destroyed by site demolition.

What I do is establish more stable, more permanent points (capped rebar or brass plugs epoxied into solid sidewalks or curbs) across the street for the construction site. I then traverse through these points and side tie the pre-existing control and boundary monuments. Sometimes I'll incorporate RTK ties as well if the site conditions are favorable for it. I adjust the lot in StarNet with the pre-existing control fixed or with a very small standard error (unless the control is found to be to loose for the purposes).

For layout control I resect my instrument positions to these newly established points.