what, in your experience, has been the accuracy of compass and chain surveys from, say, 18th and 19th century?
i am currently pursuing a 'historic' survey in my area, and got 1:900 with a suunto compass on a standee on a tripod, and measuring with a 100 foot steel tape. subsequent to correcting distances for temperature, sag, and tension, the accuracy improved to 1:1700.
when fitting different instruments together in my now colossal mosaic, i have reason to believe some of the surveys will have 1:100 accuracy
They didn't use 100ft tapes. This was a huge leap forward from chain technology.
Measure it again. (sorry, I couldn't help myself)
Steve
> They didn't use 100ft tapes. This was a huge leap forward from chain technology.
>
> Measure it again. (sorry, I couldn't help myself)
>
> Steve
OK, i want to emulate the historic survey within these reasonable bounds:
using a compass, however it is on tripod and standee. basically zero centering error
using a 100' steel tape, with corrections of temperature, sag, and tension. they will accumulate, considering the lengths of the old lines
Round Here
Typical is within 10' of distance per 1/4 mile, unless there is some sort of rough terrain.
Bearings, vary more than that.
Highly dependent on other factors. Typical NS Section lines don't vary by more than 7'. Except at points of change in declination.
EW Section lines, seem to vary more, such as up to 25', unless there are blunders.
This is my off the cuff comment, having lived it.
N
Round Here
ok then, nate. distance accuracy is only 1:130 and bearing errors would make overall accuracy worse, like a snowball effect. thanks, hope it's not going to be that severe in this survey, but i will be ready
Using a steel tape is so much easier (more accurate) than dealing with a real chain or half chain I think it taints the test more than you think. Just my opinion.
Steve
Round Here
Don't forget to bust out the isogonic chart. You probably have different declination than the original.
>1:1700
If that was all angle error, it would be 2 minutes. Can you read the compass that accurately, or was it just bad luck (offsetting errors) that made the traverse look better than it was?
I'm just working on a survey that has what I think is a chain and compass description as part of it. I can't find a recorded survey for it but I can tell by how its written it was most likely done with a chain and compass. Its a odd shaped four sided figure. On paper it misclosed by 5 feet which would be about 1 in 200. This also roughly matches what I have found in the field with the old fences. I think most of them in my area are in the 1 in 200 range, some a lot worse, and some a little better.
Consider The Original Tools Used
Prior to 1830 it was most likely a compass, 1/4° degree precision at best. If they meaned foresight and backsight they might report to 1/8°. More than likely a 1/4° was a mean from a 1/2° compass. Plus the fore and aft sights on the compass were close together.
If the deed distances are, rods, poles or perches there is a high probability they used a 2 rod chain. If they used a 2 rod chain, both chainmen may have carried a pole, to stretch the chain and keep it essentially level. More cumulative error for each reading.
Deed distances in chains imply they probably had a full chain. With a full chain there was a greater inclination to measure on the slope. If they measured on the slope they may or may not have used a locke level or inclinometer to improve their corrections or they may not have corrected at all.
I read something yesterday that when Abe Lincoln started surveying in 1833 he bought a compass but could not afford to buy a chain. Instead it is said he carried a coiled vine, which while looking unprofessional, did less to affect accuracy than one may think.
A good part of the Colonies had been already surveyed before the development of better equipment. It would be used on subdivisions and exceptions where you should find more reliable precision in those surveys.
Paul in PA
> what, in your experience, has been the accuracy of compass and chain surveys from, say, 18th and 19th century?
In Central and West Texas, the chaining typically has systematic errors as a result of:
- use of nonstandard chain,
- using 10 vara (27.78 ft.) chain plumbed by eye over chaining pins,
- holding parallel to slope of ground,
- miscounting chains.
Most of the nonstandard chains date from the colonial period before 1836 and continued to be used for decades thereafter. By the 1870's most of the chains seem to have been fairly standard. There were exceptions, however, such as one famous surveyor named Jacob Kuechler who used a 10-vara chain that were really a 10-yard chain. That introduced an systematic error of about 1:12.5 throughout his work.
I'd recommend getting a 2-pole chain and a set of 11 chaining pins and experimenting with measuring lines over varied topography with the chain suspended above the ground and plumbed by eye to see what sort of errors you find just in that.
As for directions, typically, the longer the line, the more accurate the direction is. This is because while pointing a compass over a segment 300 ft. in length may have an error of +/-5 minutes, or +/- about 0.5 ft. from true line, over a longer line with many setups of the compass, those errors accumulate at a rate proportional to the square root of the number of setups. So ten setups that align ten 300 ft. segments would have a deviation of SQRT(10) x 0.5 ft. = +/-1.6 ft. from true line, or an uncertainty in 3000 ft. of only about 2 minutes.
Naturally, other features such as the daily variation and local attraction can flood those errors with larger effects. At the latitude of Texas daily variation effects tend to be quite small and local attraction was seldom significant.
Accuracy has always been directly related to those doing the measuring and not necessarily the equipment. The same applies today whether it is steel tape, EDM or GPS.
Listen to Mr Penry
> Accuracy has always been directly related to those doing the measuring and not necessarily the equipment. The same applies today whether it is steel tape, EDM or GPS.
I watched a surveyor who rarely bothered to plumb his RTK GPS pole. He'd just "Stick it up there".
I'm not saying that the addition of 1-3 tenths broke the bank, but it was an attitude.....
N
> what, in your experience, has been the accuracy of compass and chain surveys from, say, 18th and 19th century?
I was recently reading in Brown's (Robillard's) Evidence and Procedures for Boundary Location and I believe it suggested a 1:80 precision.
> Accuracy has always been directly related to those doing the measuring and not necessarily the equipment.
That is certainly true in Texas once the issues of chain standardization are accounted for. It was a very common practice after a certain time for the chain carriers to be local residents in the area of the survey, not experienced assistants.
Some of the surveyors even later revealed the sources of some of the larger errors in even the compass work. For example, one surveyor I've followed ran about thirty miles of traverse between two springs in far West Texas in 1881 and only more than twenty years later revealed that he didn't use a flagman for the work, but simply sighted some natural feature and had his chainmen proceed toward it to the next point where he set his compass up for the next course.
It was a very common practice after a certain time for the chain carriers to be local residents in the area of the survey, not experienced assistants.
>
Kent, clarify the above statement. What is the importance of being a local as opposed to learning to chain properly, or be talented and experienced within your trade or profession?