Route Surveying for pipeline work

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> They initally set two GPS points, in this case with OPUS then traverse a few miles and tie into another set of GPS points. Problem is when they get there that they are off by about 6'. Distance from traverse to traverse vs. gps to gps is within a couple tenths but left and right 6'. I keep telling them that they need to just hold the GPS from end to end and not on just one end and rotate the field traverse to the GPS and then adjust. If your GPS points have a few hundreths of error in them when you traverse 3 miles it will explode that error way up to say about 6'. Harry doesn't seem to get the idea of rotational errors with GPS. In the past I have just used VRS to set control and then rotate and adjust.
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> Is this a similiar situation to one you guys may have had in the past?
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> Second problem is scale factor. Harry has been taking an average scale factor, in this instance 0.999896579 and scaling the control around a point in the middle. He said that the difference between ground and gid on this project is about 8' which doesn't seem like much when you think about 16 miles. o.5' in a mile is better than what these guys can close a traverse anyway but the field guys need help too (hard to believe they have been in business so long). So now to the question, how have you guys found is the best way to address this? In the past I have just done everything on grid, GPS on grid, traverse on grid, mapping on grid and had no problems but they can't seem to wrap their head around anything.
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couple thoughts
without the details of the gps base length, quality of solution, etc. you have to ask yourself whether you have good enough points to traverse 'a few miles' then measure into another gps base.
did you measure gps stations? 1 and 2, session a
2 and 3, session b
3 and 4, session c
session a sets first gps base
session b connects first gps base to second gps base
session c sets second gps base

did you?
test your edm on a CBL
check tripods, tribrachs, bubbles
set ppm values correctly
set prism constants correctly
hopefully ALL before this work started

so many others...

Perhaps you need to simply present your solutions as a cutting edge alternative without being argumentative about it hence offering a way for the guy up the ladder to save face.

It may also be time to move on, if the people at the top of a organization are no good there is really no fixing it from the bottom.

I have had this running joke in the back of my mind for years about a couples therapist who works with survey crews to improve party chief, chainman relations, if such a individual exists it sounds like they would have a little work at your shop.

What State is it in ? What coord datum are you using .

North Carolina NAD 83

The guy is not up the ladder, he has just been here for like 10 years. He is their go to guy for cad/computer stuff although his skills consist of looking stuff up on Google and You Tube. My thought is with 10 yeas to try different things and learn one would have to have it figured out by now, but I guess not.

Someone in that firm has it figured out, you need to find them and find out what was done in the past and ask some questions about why they seem to be changing the methods. You won't last 10 years like the one you are finding fault with has done using this tact. He may be an idiot but he has something to offer the company they seem to have liked. Lots of good surveyors looking for work, might think about that.
jud

In case you didn't see it, this [msg=147302]recent thread[/msg] is worth looking through.

An analysis like you suggest of taking the likely error in a GPS pair and extending it for miles SHOULD convince a reasonable person that it isn't the way to go.

The best answers come out of a least squares analysis with realistic estimates of the standard error for GPS positions, traverse angles, and distances. If that isn't possible in your office, then holding a GPS point at each end of the traverse is the next best thing.

Everything has been wrong for 10 years. This has always been a problem. This is not really a thing about Harry, I could care less about him, but we as a company need to do good work and it's just not being done now. If the company loses clients then people get laid off and companies go out of business. I do agree there are a lot of good surveyors looking for work but there are plenty of crappy wanna be's that have a job.

I guess I should have left Harry out of it but I wanted to give a background on the situation. What I should have asked is how do other companies approach route surveying with respect to GPS and the scale factor.

As for the traverse problem, it's not unique to route surveying. It sounds just as you think, and the real Harry Potter (please stand up) is an idiot.

As for scale factor, need to know more. Elevation, etc. Sounds like you need Carlson or some other survey package that will calculate the CSF at each point, but they better keep up with mark up and mark down the whole way and have a good geoid model.

Personally, the begin and end points should all be static not RTK and a sufficient distance apart to help mitigate the pointing issue. I like minimum 700'.

i've never messed with a route that long, but i would ask: what is the scale factor at each end?

We do this type of work all the time. Rotate the traverse to the ending pair and be done with it. Distances should be very close...assuming correct field/office procedures are followed.
Like Kris said, keep your initial BS distance as far as possible (700+ feet seems like a good rule of thumb)...this will help minimize error at the other end.

We stay on Grid coordinates whenever possible.

My solution would be to stay on the grid. I'm not sure how NC's SPC zones are set up, but long directional lines can cause a bit of distortion and "combined project" scale factors won't work so hot.

Here in Texas, we have long, narrow, East-West Lambert conic zones. If you're running East-West, you can maintain a pretty decent CSF. If you're running North-South, not so much.

We have the opposite problem with UTM. North-South lines work well, East-West not well at all. I had to run a East-West pipeline route and the Company insisted it be on UTM. It drove me crazy and I tried to explain to them how bad that projection was for the route, but they wouldn't budge.

Wouldn't ground distances and grid bearings make it simpler to work with? I have seen surveys using that method, allows measured distance to match the drawings over distances where it would be noticeable and grid North along the grid are all parallel at every grid line.
jud

> Wouldn't ground distances and grid bearings make it simpler to work with? I have seen surveys using that method, allows measured distance to match the drawings over distances where it would be noticeable and grid North along the grid are all parallel at every grid line.
> jud

I suppose ground distances would be just as easy to work with. Personally, I like State Plane Coordinates. The geo-referenced data, and consistent coordinate system is invaluable. That's why I like to stay on grid. I did things different when I was the only surveyor working here. For us it is simpler to see a coordinate like N 558087.00, E 2375752.00 and know that it is SPC, and not some manipulated ground-hybrid thereof.
I switch to ground when needed (often)...but our default is grid.

> My solution would be to stay on the grid. I'm not sure how NC's SPC zones are set up, but long directional lines can cause a bit of distortion and "combined project" scale factors won't work so hot.
>

FYI, North Carolina has only one zone.

Larry P

> Wouldn't ground distances and grid bearings make it simpler to work with? I have seen surveys using that method, allows measured distance to match the drawings over distances where it would be noticeable and grid North along the grid are all parallel at every grid line.
> jud

Jud, let's do some supposing.

Suppose you had a pipeline project, say 50 to 100 miles. Also suppose that from one end of the project to the other had some significant changes in the combined factor.

Which combined factor are you going to use to convert grid to ground?
Hold one end and convert the entire project?
Create an average and use that for the entire project?
Heaven forbid you decide to break the project into small chunks and apply lots of factors.

No, trying to work using ground coordinates brings in way more complications than the few it solves.

Larry P

1. Like Kris, I need to know your software? Carlson would do the job as
he explained.

2. Most route surveying is open end traverse, which has no checks?

3. NC is a Lambert zone. Scale factors do not change much as you
traverse east and west.

4. As mentioned, RTK is not a very confident solution to truth transit-traverse.

5. Taking star shots on the ends and every four miles of traverse might localize
an angular error quickly.

6. Although we surveyors have great confidence in GPS, you need more than checking
the two endpoints to diss transit-traverse precision.

7. Assuming all traverse angles were turned perfectly except one. Were all angles
doubled or two sets of angles turned at each traverse point?

8. I've seen MMM's swing technique used in open end traverse; it is bogus because
it throws all of the angular error in the swing point.

Your dissing of using many scale factors is not any big deal in Carlson software.
I hope your continuing education is good enough to educate NC DOT, TX DOT, UT DOT,
and MO DOT who use a fixed scale factor for a district or one scale factor for the
project or multiplying the coordinate positions by the factor (in error).

First of all opus will have an error in it sometimes tenths of a foot . A couple hundred foot backsight will produce crappy results miles down the road . Set opus only to get you on grid and then static local control in from the couple opus points this will give you better results . Also keep your control closer and set pairs every mile or so . you start an new trav every mile . Stay on Grid coords the entire project . Have you checked your total station , your poles ,have you set the temp in the gun, have you doubled angles? Run it through least squares and it will be fine .