Proper procedure to double angles when staking out

I turn out my known angle, and put a stake in the ground. Then put the plumb bob up and drill a small hole on line. Then rebacksight on face-two (or whatever terminology you use) and turn out the angle again, and we drill another hole if it doesn't match precisely. The rod man/woman sets a sight tack on the split of the two holes and you sight that split. Presumably you set the stake past the point where you want to set the monument. I like shooting to the center of the tack, and taping back the overage and getting line from the instrument-man (who sighted the tack). It takes longer than setting a rod right at the distance and angle. But I like the method better.

How much of a distance do you see between the two faces?

15", but that's probably not all instrument error (it's a 10" or 20" instrument...opinions vary). Some of it could be prism sway error. If you mean how much calculated distance that is, it's .02' at 288' +/-.

I could replace the Prism Wife with a tripod and plumb bob and re-measure the point we've staked, and if it's off, calculate the difference and move the mark...measure again, then take the mean between the two, something similar to Mark Chain's method.

> I set up on a known point and backsight to another known point at right angles to the property line I want to re-trace.

Okay, I'll admit that I haven't followed every installment of this saga, but when I read a non-licensed amateur surveyor with at best a very tenuous-sounding grasp of the ordinary measurement operations of surveying writing about retracing property lines, I have to wonder what he is actually trying to do and why. What did I miss?

> > I set up on a known point and backsight to another known point at right angles to the property line I want to re-trace.
>
> Okay, I'll admit that I haven't followed every installment of this saga, but when I read a non-licensed amateur surveyor with at best a very tenuous-sounding grasp of the ordinary measurement operations of surveying writing about retracing property lines, I have to wonder what he is actually trying to do and why. What did I miss?

Kent:
Please, give the "non-licensed amateur" thing a rest. You didn't miss anything. Yes, I'm an amateur. Yes, I'm a student. Yes, I'm reading Ghilani and Wolf, cover to cover. And, YES, I'm using my wife's 25 acre parcel, all of which has already been surveyed, as a real world "arena" for my field work. What better way to learn field work than to go from one previously surveyed pin to another? What better way to learn increased precision by running network traverses and applying least squares etc.? What better way to learn the use of an instrument than to use an instrument. Any ideas?

There's NOTHING in Ghilani and Wolf written specifically about what I'm trying to learn, nor describing the very practical method Mark Chain offered. I know that most in my place would go to work for an LPS to learn "ordinary measurement operations", but I don't have that opportunity, given that I already have a 60 hr/week job. Many of you studied this in school, many years ago. I did not.

So I rely on many of the good folks here to take their time explaining how they do this in the real world. If you think it would help prevent getting your and others hackles up, should I preface every future question with some kind of disclaimer, like "THE FOLLOWING QUESTION IS STRICTLY FOR EDUCATIONAL PURPOSES ONLY"?

I have every right to do this; I don't need a license, nor do I need to hire a LPS to do what I'm doing.

End rant. Thanks for listening.

I turn the angle in face 1, set something on line (typically a hub with a target), then sight face 2 to backsight, zero, and turn to set target. I then mean the angles, and move the target to the new line, and use that to set the final position.

But, if the difference is only one hundredth, the whole process is possibly not needed.

> Please, give the "non-licensed amateur" thing a rest.

Actually, it's an important distinction. You aren't merely doing some field exercises to practice the mechanical operations of surveying. As I understood your post, you're attempting to locate a land boundary that presumably defines the limits of someone else's property.

> You didn't miss anything. Yes, I'm an amateur. Yes, I'm a student. Yes, I'm reading Ghilani and Wolf, cover to cover. And, YES, I'm using my wife's 25 acre parcel, all of which has already been surveyed, as a real world "arena" for my field work. What better way to learn field work than to go from one previously surveyed pin to another?

Well, for starters, why not learn how to measure angles with the instrument that you have? Does the manufacturer describe the process in the Instruction Manual that was originally supplied with the instrument? It isn't rocket science, but without knowing how to get results of predictable quality from the equipment, everything else is an exercise in futility.

> What better way to learn increased precision by running network traverses and applying least squares etc.?

I'm afraid that starting at the basics is the best way to learn. If you're trying to run traverses without knowing how to make accurate survey measurements of uniform quality, then you've skipped Steps One through at least Four.

> What better way to learn the use of an instrument than to use an instrument. Any ideas?

Yes. Reading the manufacturer's instructions is Step One before using the instrument. Step Two is reading a description of the errors that enter into measurements with a total station, both centering and measurement of angles and distances. Step Three is
testing the basic adjustments of the instrument. Step Four is testing the accuracy of an angle measured with the instrument (by the method I've previously described here). Step Five is testing the accuracy of various targets and methods of centering them over ground marks.

After Step Five, you should be able to at least measure angles with some predictable uncertainty, so you move on to pre-flight checks relating to distance measurements. Otherwise, you're just radioing the control tower for advice on how to turn the airplane when you're a few thousand feet up.

Thanks. That sounds even simpler than Mark Chain's, but I'll try both, and compare the results. Not interested in distance at this point.

rfc, to me, life is like baseball. You don't have to swing at every pitch.

Here's a link to a good book:

Construction Surveying and Layout by Wesley Crawford

Lol!
I was ready to, but thought better of it.
Thanks for the link.

> rfc, to me, life is like baseball. You don't have to swing at every pitch.
>
Excellent reference. We just watched the move "42" last night. That man knew when to hold 'em.

Thank you Kent!

> Reading the manufacturer's instructions is Step One before using the instrument. Step Two is reading a description of the errors that enter into measurements with a total station, both centering and measurement of angles and distances. Step Three is
> testing the basic adjustments of the instrument. Step Four is testing the accuracy of an angle measured with the instrument (by the method I've previously described here). Step Five is testing the accuracy of various targets and methods of centering them over ground marks.
>
> After Step Five, you should be able to at least measure angles with some predictable uncertainty, so you move on to pre-flight checks relating to distance measurements. Otherwise, you're just radioing the control tower for advice on how to turn the airplane when you're a few thousand feet up.
>

Aloha, Kent:

I trust you are enjoying your long weekend!

As a perpetual student of Land Surveying--non licensed--I really appreciate steps outlined so clearly here by you!

Btw, I also printed out the entire discussion of two posts you posted on "Testing Centering Accuracy of Prism... and Testing Direction Accuracy of TS." Thanks to you and others who contributed to that discussions.

I have to admit those discussions was a bit challenging for me to follow as I am just getting familiar with many of the technical terms. I hope you will continue to post more these type of fundamental subjects. :good:

P.S: I of course had our land surveyed by a PLS. And only "play" within these boundary lines. 🙂

RFC; allow a lurker to give you some more basic info:

I have engaged in an odd hobby the last several years; reading most of the rules and regs for the 50 states regarding land surveying. The general rule is virtually the same in all states; you can survey your own land as long as you are not offering services to the PUBLIC that a licensed land surveyor is solely allowed to lawfully offer. Those specific items of surveying are always listed at the state website as to what constitutes land surveying. There are usually 8 to 15 or more items or subjects that a particular state website and board calls land surveying.

As far as your attempt at learning angle measuring; first it depends on what type of instrument you are using.

1.An old engineer's transit with a vernier and magnifying glass over the reading plate
2. a theodolite with an upper and lower motion(two sets of thumbscrews for operating the upper and lower plates or circles called a repeating instrument) or a theodolite with just one plate motion and one set of thumbscrews,(called a direction instrument)
3. Then there is the total station.

For example, I trained my son on the Wild T-16 theodolite which is a repeater.

The whole idea is to remove as much instrument error as you can; I won't get into personal or environmental errors here.

To do that you need to take readings with the scope in it's regular (direct position, and then the readings have to be taken with the scope upside down, called the plunged or reverse position. This is called by most manufacturers and guys on this website as Face 1 and Face 2 or similar jargon.

The circle or plate is not perfectly graduated and has errors built into it. The way to take this error out is to use the entire plate by turning enough sets of angles that use the entire plate. For ex., after you have turned your first 90 deg angle, on the repeater theodolite you would lock the upper motion so that the 90 degree reading does not change. Then plunge the scope to the reverse(inverse) position and back sight to the zero mark with the lower motion, leaving the upper reading plate still locked. Now loosen the upper motion and turn until you are reading 180 degrees. My T-16 misses the first temp set point by 0.01 feet in 100 feet, so I make the half-hundredth adjustment that splits the error to the fore sight point.

That is comprises one set of angles,just the basic idea. If you want to turn more sets, then use the formula 180/n to know how much to advance the plate for the next set,where n is the number of sets. So four sets,n=4 and 180/4=45 degrees. So the plate would then have to be set to 45 degrees instead of zero when back sighting to start the second set of angles. The third set would use 90 deg as the plate setting to start at the Back sight. And so forth. That way you will be using the entire plate for readings and be close to completely eliminating instrument error.

I still get out the T-16 when I am working with a engineering student from the local college; surveying was dropped from the curriculum a while ago. I feel obligated to teach them the basics, otherwise they are like their classmates; button-pushers. The only way to really get them interested and involved is to pay them out of your pocket,even though their production amounts to a business loss.

Thank you Kent!

> Btw, I also printed out the entire discussion of two posts you posted on "Testing Centering Accuracy of Prism... and Testing Direction Accuracy of TS." Thanks to you and others who contributed to that discussions.
>
> I have to admit those discussions was a bit challenging for me to follow as I am just getting familiar with many of the technical terms. I hope you will continue to post more these type of fundamental subjects.

I don't believe that you'll find either of those topics treated in that detail in a surveying text. I'm sure that any questions on either would be welcome. It may sound condescending to suggest that the fundamentals are where to begin, but that is truly the most direct path toward proficiency.

Thank you Kent!

> I don't believe that you'll find either of those topics treated in that detail in a surveying text. I'm sure that any questions on either would be welcome. It may sound condescending to suggest that the fundamentals are where to begin, but that is truly the most direct path toward proficiency.

Aloha, Kent:

You are right...non of the books I have give that much detail. Will post questions as I work on them.

No, I don't think it sounds condescending at all! It is a very sound advice!

I give this as lesson one.

Imagine a telescope with cross hairs that are offset to the left, by a small amount Say 1 arc minute. On this LEFT side of the inst, you place a small chalk dot. You set ZERO on a backsite. Then, you flop the gun, and set another stake some 200' away. This places a kink in the straight line, at the instrument. And the kink is a small deflection to the RIGHT. (Remember, we are looking with an inverted scope at the foresite, so it is a kink toward the chalk dot on the now right side of the inst). Now, leave the scope inverted, and spin the inst 180°, to the backsite again. Now, the chalk dot is on your RIGHT. Set it perfectly. Now, flop the inst, and look at the foresite. Now your chalk dot is on your LEFT, as you look at the foresite, and you are some 0.12' to the left of your previous mark. NOW, you split the two dots on the foresite, and you have PROJECTED a straight line, with an instrument, that is consistently out of adjustment, by one arc minute.

What Kent above says about the idea that you area already flying, and now you are radioing the tower, with instructions on how to land, is true.

Unfortunately, that was how I learned. This means that I am quite able to explain some of this stuff, and some of it I am weak in some of the details.

What Kent is trying to say is that if we get you on the ground, then you will STILL be weak in some of this stuff. And, that, he does not want.

Kent is capable of being rude, but sometimes, it just looks rude, when really there is an important concept behind his abruptness. Kent is pretty smart, and you can learn from him.

My opinion on the above. Ok?

N

>I'm afraid that starting at the basics is the best way to learn. If you're trying to run traverses without knowing how to make accurate survey measurements of uniform quality, then you've skipped Steps One through at least Four.

And... game, set, match.

I give this as lesson one.

> Imagine a telescope with cross hairs that are offset to the left, by a small amount Say 1 arc minute. On this LEFT side of the inst, you place a small chalk dot. You set ZERO on a backsite. Then, you flop the gun, and set another stake some 200' away. This places a kink in the straight line, at the instrument. And the kink is a small deflection to the RIGHT. (Remember, we are looking with an inverted scope at the foresite, so it is a kink toward the chalk dot on the now right side of the inst). Now, leave the scope inverted, and spin the inst 180°, to the backsite again. Now, the chalk dot is on your RIGHT. Set it perfectly. Now, flop the inst, and look at the foresite. Now your chalk dot is on your LEFT, as you look at the foresite, and you are some 0.12' to the left of your previous mark. NOW, you split the two dots on the foresite, and you have PROJECTED a straight line, with an instrument, that is consistently out of adjustment, by one arc minute.
>
>
Thanks for describing the technique.
I don't expect everyone to read carefully, the questions I ask, and I'll grant that my language skills are not always the best.

That said, I am NOT asking for instructions on "making consistent angle measurements" with the instrument I'm using--I've been doing that; getting increasingly accurate measurements; have learned where the errors are coming from, and making corrections when needed. I know how to turn angles, how to double, and how to identify and correct both systematic and random errors in the measurements.

What I was asking (and got three excellent answers--yours included), was: What field techniques are typically used to find the spot when you know the angle, as opposed to finding the angle when you know the spot--while still using procedures to remove systematic errors in the measurement. That calls for slightly different techniques, as the responses from Mark Chain, dmyhill and you bear out.

That to me is not akin at all to asking for "instructions on how to land the plane" when you don't know how to fly. It's more like learning to use the VOR or GPS instruments to find the airport closest to your (known) track, as opposed to finding the track to your destination airport.

Different objective; different procedure.

:good:
Crawford's book is a good one for the type of questions being asked here. Explains everything in detail.