Control network--first baby step

A LS adjustment of a loop is almost identical to a Compass closure of a loop.

LS becomes necessary once you have two loops. Redundancy cannot be properly adjusted in the standard traverse closures.

I would suggest reviewing Carlson's SurvNet. Also, you can use F2F with proper coding to keep track of existing and lost points.

I was always taught to avoid crossing traverse lines if at all possible. Undoubtedly you will need to cross some at some point, I mean line...

I would start with a perimeter loop. Or at least a loop that is as large as possible. Follow standards of care with decent angles, avoid those close to 180 when possible. With the core, you can then start some sub-loops.

When are you getting the GPS involved?

>angles, avoid those close to 180 when possible

I believe that is a truth from one situation that has been perpetuated into situations where it does not apply. If you are finding a point by intersecting lines with measured angles, then it is true that small angles or those close to 180 are bad. If you are measuring angle and distance with approximately the same relative accuracy, it really doesn't matter much what angles you have.

> Aloha,
>
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>
> Can a control network created with traverse adjustment or it must be done with Lease Square Adjustment?

You can used a simple traverse and traverse adjustment as the start of a control network. I would suggest the traverse angular closure as well as the coordinate (Difference in Northing and Easting) closure be checked. If either is below your desired tolerance you will need to search for errors in the traverse.

>We are talking about 70+ acres. What are the closure tolerance for a good control network?

This depends on the planned future use of the network. As recently as 30 years ago control with a closure ratio of 1:5000 was considered sufficient for engineering and construction of small projects.

In Ohio the minimum standards for property boundary surveys, 4733-37-04 Measurement specifications, is "(allowable linear error = reported distance divided by ten thousand)" or a ratio of 1:10,000. That would equal just over one foot of error (1.056 ft) in two miles of traverse measurement. With the equipment available today and careful work students in my introductory surveying class commonly achieved 1:20,000 to 1:50,000 closures. Their training traverse was approximately 2,400 feet long.

>
> What should be my next step to establish a good network of control points?
>

The following would be my list of parts to the next step:

• ... Determine what type of monuments you need (reinforcing rod, iron pipe, driven rod, pin or pipe in concrete, etc.) for the points to remain stable. Also will this be a 3D (North, East, Elevation) control network? Vertical stability may require a different type of monument.
• ...Determine the approximate location of a traverse just inside the property lines. Have at least two traverse monuments visible (3 is better) from each monument. If possible include a few additional traverse lines across the outer traverse. East side to West side, North side to South side or diagonal.
• ...Check closure on the outer traverse and, if acceptable, adjust. I suggest compass adjustment, without prior adjustment of the angles.
• ...If you have traverse lines across the outside loop hold the adjusted coordinates at beginning and end of the crossing line to adjust.
• ...If vertical is included follow the same pattern working from the outside inward, large to the small, whole to the parts. This tends to reduce the apparent errors in both horizontal and vertical. Working from the small to the large may have the opposite result.

Aloha, J:
Thanks for the reply!

> A LS adjustment of a loop is almost identical to a Compass closure of a loop.
>
> LS becomes necessary once you have two loops. Redundancy cannot be properly adjusted in the standard traverse closures.
>
When you say "two loops" does that means you make two different traverse loops and use both loops to do the LSA? And this two loops could have common traverse points that they share hence the "redundancy?"

> I would suggest reviewing Carlson's SurvNet. Also, you can use F2F with proper coding to keep track of existing and lost points.
>
I looked into Carlson and other software and they are beyond what I can afford. I have TraversePC which is capable of doing LSA but I don't how to use it just yet.
What do you mean by existing point and lost points?

> I was always taught to avoid crossing traverse lines if at all possible. Undoubtedly you will need to cross some at some point, I mean line...
>
I can work toward not having the traverses line cross each other...

> I would start with a perimeter loop.
Okay, I can begin to work on this as my first step.

Or at least a loop that is as large as possible. Follow standards of care with decent angles, avoid those close to 180 when possible.
I noticed Bill commented on this.

With the core, you can then start some sub-loops.

"sub-loops" smaller loops within the perimeter loop right?
>
> When are you getting the GPS involved?
I don't have GPS setup; it is beyond my reach at this time--literally and financially;-) . So all will be done with TS. However, I did start to learn a bit about GPS. I follow a lot of the posts about GPS here and almost 90% of the discussion goes way over my head! OPUS, RINEX etc. I thought they were mammals existed before the ice age 😀

Why not try it to adjust long hand, that would be a good training session which will provide you satisfactory results. If you google latitudes and departures, you should find examples and procedures to follow.

> Why not try it to adjust long hand, that would be a good training session which will provide you satisfactory results. If you google latitudes and departures, you should find examples and procedures to follow.

Have not checked the accuracy of the data in the link. However Adjusting a traverse page may be of help.

Aloha, Dallas: Thank you so much for the detailed response! See my notes below...

> > Aloha,
> >
> ---------------- QUOTE CLIPPED ------------------
> >
> > Can a control network created with traverse adjustment or it must be done with Lease Square Adjustment?
>
> You can used a simple traverse and traverse adjustment as the start of a control network. I would suggest the traverse angular closure as well as the coordinate (Difference in Northing and Easting) closure be checked. If either is below your desired tolerance you will need to search for errors in the traverse.
>
Okay this is clear to me.

> >We are talking about 70+ acres. What are the closure tolerance for a good control network?
>
> This depends on the planned future use of the network. As recently as 30 years ago control with a closure ratio of 1:5000 was considered sufficient for engineering and construction of small projects.
>
> In Ohio the minimum standards for property boundary surveys, 4733-37-04 Measurement specifications, is "(allowable linear error = reported distance divided by ten thousand)" or a ratio of 1:10,000. That would equal just over one foot of error (1.056 ft) in two miles of traverse measurement. With the equipment available today and careful work students in my introductory surveying class commonly achieved 1:20,000 to 1:50,000 closures. Their training traverse was approximately 2,400 feet long.
>
I am careful with my work and I will strive to achieve 1:20000 to 1:5000 closure. I will check out the link above.
> >
> > What should be my next step to establish a good network of control points?
> >
>
> The following would be my list of parts to the next step:
>
>

• >
• ... Determine what type of monuments you need (reinforcing rod, iron pipe, driven rod, pin or pipe in concrete, etc.) for the points to remain stable. Also will this be a 3D (North, East, Elevation) control network? Vertical stability may require a different type of monument.
  I want to carry my elevation. Was thinking about cotton gin pin in concrete to distinguish it from the 1/2" set by my PLS for the boundary lines.

  >

• ...Determine the approximate location of a traverse just inside the property lines. Have at least two traverse monuments visible (3 is better) from each monument. If possible include a few additional traverse lines across the outer traverse. East side to West side, North side to South side or diagonal.
  Okay, I understand this and I can do that.

  >

• ...Check closure on the outer traverse and, if acceptable, adjust. I suggest compass adjustment, without prior adjustment of the angles.
  Compass adjustment is lat. and dep. right?

  >

• ...If you have traverse lines across the outside loop hold the adjusted coordinates at beginning and end of the crossing line to adjust.
  I didn't understand this one...sorry! Let me study this a bit perhaps with a sketch.

  >

• ...If vertical is included follow the same pattern working from the outside inward, large to the small, whole to the parts. This tends to reduce the apparent errors in both horizontal and vertical. Working from the small to the large may have the opposite result.
  Is there an example you can share on this?

  >

Thanks again for all the insights Dallas!

You might check with your surveyor. He would have had to run a control network to determine/survey/mark your boundary . Ask him if he will share his control and boundary information with you.

> Why not try it to adjust long hand, that would be a good training session which will provide you satisfactory results. If you google latitudes and departures, you should find examples and procedures to follow.

Aloha, James: I just purchased Barry Kavanagh's Surveying Principles and Applications. I think he explains it how to adjust long hand. I am just beginning to study it.

Related question...when I traversed and have a loop. Then I do the necessary adjustment to get best closure. Now the points in ground is no longer accurate right? They will have new coordinates. Do you have to redo the monuments to reflect the adjusted new position. If no...then when I setup on the this points for any future work, wouldn't the accuracy of that work be questionable?

I really appreciate yours and everyone's patients answering my questions!!

> You might check with your surveyor. He would have had to run a control network to determine/survey/mark your boundary . Ask him if he will share his control and boundary information with you.

Aloha, Kevin:
My PLS was very generous. He knows I am no competition to him 😉 He shared all the field data his crew collected in ASCII file format. So I got the coordinate. He do not have any network. They had several baselines (?) created with their RTK GPS setup. From there his crew work with their TS.

I asked him about creating Control Network. His answer was "you don't need do that" :-/

Your raw data is unadjusted. By adjusting the traverse, you are correct, you have a new set of coordinates; the adjusted coordinates. Those are the ones you would use moving forward if you are satisfied with the results of your adjustment by latitudes and departures.

Do you have descriptions to accompany the coordinate file?

Sounds like he established a handful of RTK GPS control points and ran his terrestrial traverse off of that. You have his control, but you just don't recognize it. I would try to determine what his control points were (and where they are)... nails, rebar, pipes etc.

Enjoy!

> Do you have descriptions to accompany the coordinate file?
>
> Sounds like he established a handful of RTK GPS control points and ran his terrestrial traverse off of that. You have his control, but you just don't recognize it. I would try to determine what his control points were (and where they are)... nails, rebar, pipes etc.
>
> Enjoy!

Aloha, Kevin:
Each point in the file do have descriptions; however, he didn't carry the elevation. There are total of seven of them that he established with RTK GPS. He use 1/2" pipe for those. Other traverse points are either hub and tack or mag nails. I have located all of them physically and have them protected.

> Your raw data is unadjusted. By adjusting the traverse, you are correct, you have a new set of coordinates; the adjusted coordinates. Those are the ones you would use moving forward if you are satisfied with the results of your adjustment by latitudes and departures.

Aloha, James: I think I understand what you wrote here. But...
Let say I have traversed through five points A, B, C, D and E. The distant between B and C is 100' and the AZ is 160º 30' 00"
If the end of the C is adjusted during the adjustment, would't that change distance between B and C when I setup on point B and take shot to point C? During traverse the data collected had a different coordinates and after adjustment I have different coordinates that I am using to setup and to backsight between these two points.

Thank you!

Yoginatha,
For your purposes you shouldn't need a really tight control network. I would begin by setting up a traverse all the way around the property. It will be obvious that in some areas your traverse point will likely be destroyed. Use 30d nails (or other inexpensive, simple mark) for those. In areas that are more secure, set a long rebar with concrete around it (or other more durable mark). Remove brush and undergrowth so that you have clear lines of sight from point to point. Try to strategically set your marks so that you can see monuments and features that you want to locate. You may have an area or two that you can see across the middle of the property. You might have to have several set ups to get from one side to the other. We like to have all the points set and brush cut before we take the instrument out of the box. The longer the instrument sits on a point the more it will settle or drift, so we try to turn the angles and measure the distances to the traverse points first and sideshots to monuments or features last. Turn the number of sets needed to meet your standard. I would think that two angles per point would be enough for your purposes. The least squares program I use needs "degrees of freedom" to adjust the data. Redundancy, redundancy, redundancy. The more angles/distances to each point, the more confident your solution is.

> > The following would be my list of parts to the next step:
> >
> >

> >
• ... Determine what type of monuments you need (reinforcing rod, iron pipe, driven rod, pin or pipe in concrete, etc.) for the points to remain stable. Also will this be a 3D (North, East, Elevation) control network? Vertical stability may require a different type of monument.

> I want to carry my elevation. Was thinking about cotton gin pin in concrete to distinguish it from the 1/2" set by my PLS for the boundary lines.

Changes in soil moisture and freeze thaw tend to be more of a disturbance vertically than horizontally. Local soil types and depth to bed rock also should be considered. Trigonometric elevations with a total station can be good. Direct leveling, surveyors level and level rod, are usually more accurate.

>
> >

• ...Check closure on the outer traverse and, if acceptable, adjust. I suggest compass adjustment, without prior adjustment of the angles.

> Compass adjustment is lat. and dep. right?

Lat. difference and Dep. difference when you return to end your traverse on your beginning point define your error of closure. Compass Rule is a math equation used to spread that error through your traverse and cancel out the error. See the link in my response to James Johnston of an explanation and the equation.

>
> >

• ...If you have traverse lines across the outside loop hold the adjusted coordinates at beginning and end of the crossing line to adjust.

> I didn't understand this one...sorry! Let me study this a bit perhaps with a sketch.

Once you have applied the compass rule equation to your outside traverse the coordinate (North and East) values of those points become fixed. The connecting lines begin at fixed North and East values and end at fixed North and East values. When you compute your crossing line traverse the end values WILL NOT match your fixed North and East values. Use the compass rule equation again on only the crossing traverse line to correct the error. This is creating the loops others have mentioned. LSA adjustment programs will handle multiple loops in one pass and produce results very close to what I am describing.
>
> >

• ...If vertical is included follow the same pattern working from the outside inward, large to the small, whole to the parts. This tends to reduce the apparent errors in both horizontal and vertical. Working from the small to the large may have the opposite result.

> Is there an example you can share on this?
>
May have something that will help. Will take a while to find that and get back to you. Do you have any surveying texts available to you? I may be able to direct you to chapters that will help you.

> Thanks again for all the insights Dallas!

You are very welcome. I enjoy helping you understand the basics.

 

It would be a lot of fun to run your own traverse through his points and compare your coordinates with his when you're done. Try not to peak as you go. You may surprise yourself or maybe realize how tough the surveyor's job really is. 🙂

Aloha, Stacy: Thank you the great suggestions!

> For your purposes you shouldn't need a really tight control network.
I agree 100%. I tend to set very high standard for myself work hard to achieve that standard. That helps me stay within the margin when I get sloppy. Not just in survey but in every aspect of my life as monk 🙂

I would begin by setting up a traverse all the way around the property. It will be obvious that in some areas your traverse point will likely be destroyed. Use 30d nails (or other inexpensive, simple mark) for those. In areas that are more secure, set a long rebar with concrete around it (or other more durable mark).
Will do this. Some places on the property we run heavy equipment regularly. It is almost impossible to preserve this.

Remove brush and undergrowth so that you have clear lines of sight from point to point. Try to strategically set your marks so that you can see monuments and features that you want to locate. You may have an area or two that you can see across the middle of the property. You might have to have several set ups to get from one side to the other. We like to have all the points set and brush cut before we take the instrument out of the box.
Great idea!

The longer the instrument sits on a point the more it will settle or drift, so we try to turn the angles and measure the distances to the traverse points first and sideshots to monuments or features last.
Will do this.

Turn the number of sets needed to meet your standard. I would think that two angles per point would be enough for your purposes. The least squares program I use needs "degrees of freedom" to adjust the data. Redundancy, redundancy, redundancy. The more angles/distances to each point, the more confident your solution is.
Thanks for the emphasis on redundancy Stacy!

> > > The following would be my list of parts to the next step:
> > >
> > >

> > >
• ... Determine what type of monuments you need (reinforcing rod, iron pipe, driven rod, pin or pipe in concrete, etc.) for the points to remain stable. Also will this be a 3D (North, East, Elevation) control network? Vertical stability may require a different type of monument.

> > I want to carry my elevation. Was thinking about cotton gin pin in concrete to distinguish it from the 1/2" set by my PLS for the boundary lines.
>
> Changes in soil moisture and freeze thaw tend to be more of a disturbance vertically than horizontally. Local soil types and depth to bed rock also should be considered. Trigonometric elevations with a total station can be good. Direct leveling, surveyors level and level rod, are usually more accurate.
>
Fortunately, we don't have freezing issue here! However, soil do the get soft due to a lot of rain. For my purposes trig level would be sufficient I think.
> >
> > >

• ...Check closure on the outer traverse and, if acceptable, adjust. I suggest compass adjustment, without prior adjustment of the angles.

> > Compass adjustment is lat. and dep. right?
>
> Lat. difference and Dep. difference when you return to end your traverse on your beginning point define your error of closure. Compass Rule is a math equation used to spread that error through your traverse and cancel out the error. See the link in my response to James Johnston of an explanation and the equation.
>
> >
Thanks. This is clear now. I also read the link which defines various adjustment.
> > >

• ...If you have traverse lines across the outside loop hold the adjusted coordinates at beginning and end of the crossing line to adjust.

> > I didn't understand this one...sorry! Let me study this a bit perhaps with a sketch.
>
> Once you have applied the compass rule equation to your outside traverse the coordinate (North and East) values of those points become fixed. The connecting lines begin at fixed North and East values and end at fixed North and East values. When you compute your crossing line traverse the end values WILL NOT match your fixed North and East values. Use the compass rule equation again on only the crossing traverse line to correct the error. This is creating the loops others have mentioned. LSA adjustment programs will handle multiple loops in one pass and produce results very close to what I am describing.
> >
Okay this is clear now.
> > >

• ...If vertical is included follow the same pattern working from the outside inward, large to the small, whole to the parts. This tends to reduce the apparent errors in both horizontal and vertical. Working from the small to the large may have the opposite result.

> > Is there an example you can share on this?
> >
> May have something that will help. Will take a while to find that and get back to you. Do you have any surveying texts available to you? I may be able to direct you to chapters that will help you.
I have two books Charles Ghilani's Elementary Surveying and Barry Kavanagh's Surveying Principles and Applications. I just began to study both these books. Got started with Mr. Kavanagh's first which appears easy to understand.
>
> > Thanks again for all the insights Dallas!
>
> You are very welcome. I enjoy helping you understand the basics.
It is very much appreciated and means a lot to me!