Hi Guys
I've been surveying for just over a year. At college it was drummed into us to always close a traverse and so that what I've been doing. With thoughtful station positioning I can almost always find a decent way.
However sites like the on in this diagram pose a problem. The house is split over two plots of land. There is a thick wall in the centre of the house to divide it up - this is a fairly common arrangement in the UK.
Of course its possible to do close loop traverse on this site but it doesn't really lend itself to it as you cannot go around the perimeter in a loop. Its possible to make a loop around the open side of the house but this involves a number of additional necessary stations.
What alternative are there? What do you guys do in the real word?
Best regards, Andrew
In reality you can not just survey 1/2 of a double. As a surveyor you need to survey both halves, but not necessarily disclose all information that some might consider a "freeSurvey" on your map. If corners were set in the past, you would be locating at least 6 markers. Easiest way to show is broken line "ties" to the corners on the right parcel. In many cases no markers were set and the only monuments you have are the houses themselves. Then it is necessary to show the entire building and the splits from the corners. There are times when you find that both halves of a double were not built at the same time. Let us assume that your PQ side was constructed first, the common wall could be entirely on the left lot. When the right half was erected they built to the face. The center of the common wall does not become a new lot line, but in essence the dwelling to the right has marginally more interior area. Were the left house to be demolished the entire common wall on that side would have to remain as support for the right dwelling. One should be able to obtain permission to enter the right welling yard are to do the survey, but that is not always the case. It is not uncommon to run a survey line through the dwelling. In the majority of cases one can reliably hold the splits, occasionally a common wall may be off angle to the lot line. In that case you give some left and right offsets but you do not use such words as "encroachment". As long as the line is within the wall +/- 0.10' there is no need to consider any type of lot line adjustment/agreement.
A few years ago I surveyed an entire block for one single family dwelling, 2 doubles to the East and row houses to the West. The most adjacent double split to the East was more than a foot off the lot line, but since it had been erected before the map was filed it was shown out of place on the filed map, but did not affect the lot lines for any other purpose.
Paul in PA
As for a closed loop traverse, save that for your control network. Your lot is small, correct?
An open leg will not be a problem on the lot itself. One way is to set two points when getting ready to traverse.
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Set and sideshot a point that can be observed from where you're set up and where you're going to traverse to. Set another point to traverse to. Pick up, set up and backsight your previous TP. Turn to the point you set as a sideshot point as a check. This could work better if the check shot was a "control" point.
This is not a recommended practice to adjust a network. It's just a way to confirm your backsight orientation is good. Today's modern equipment and good survey practices should negate and blunders on a small lot survey once you get the control to the site.
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Another option is to burn two GPS point to serve as tp 1 bs tp 2 and two closing GPS points to serve as a known closing leg.
You have to balance the cost of the survey to what you're prepared to do in the field
If you only need two control points then only use two.?ÿ Last shot is to the original backsight, and the difference is your closure.?ÿ
Always double or do more repetitions at each setup and turn doubles to your monuments and most important points of the location.
Repeat any observations that do not fall within your instrument's capabilities, aka tolerances.
Geez, we ain't building' watches, ya know?
Set on one point and shot the 4 corners of a quarter section, then split it in half, then created a six-sided tract out of one of the halves. ?ÿThen, rezeroed and shot everything a second time as a check. ?ÿDone.
Hi Guys
I've been surveying for just over a year. At college it was drummed into us to always close a traverse and so that what I've been doing. With thoughtful station positioning I can almost always find a decent way.
However sites like the on in this diagram pose a problem. The house is split over two plots of land. There is a thick wall in the centre of the house to divide it up - this is a fairly common arrangement in the UK.
Of course its possible to do close loop traverse on this site but it doesn't really lend itself to it as you cannot go around the perimeter in a loop. Its possible to make a loop around the open side of the house but this involves a number of additional necessary stations.
What alternative are there? What do you guys do in the real word?
Best regards, Andrew
If you tie to the same point (building corner or something else) from a different setup point you are in effect "closing the traverse" between those setup points.
If you get the same calculated position from both ties, you are good.
another way... make cross ties on your "open traverse"... no angle is necessary to use that as a check.
Think "measure everything twice with different methods"... at least the critical parts
Something I wish was taught is the difference between "condition equations" and "observation equations."?ÿ A closed loop traverse is basically a condition equation: the condition is that the sum of interior angles of the whole figure equal (n-2)*180, and if not, adjust accordingly. Before the age of electronic calculators and computers, it was the only way to adjust anything in a reasonable amount of time. Once electronics came along, it became feasible to use "observation equations," wherein all the angle and distance observations (polar form) are converted into coordinates (rectangular form) and then a weighted mean is calculated from all the coordinates of a point. From there it evolves to least squares and all the fun stuff. Remember that the British Empire was mostly surveyed by intersections to points never occupied from resection occupations that were never intersected.?ÿ (With thanks to Mike Potterfield for posting that info about condition and observations equations on the old board about ten years ago.)?ÿ
In reality you can not just survey 1/2 of a double. As a surveyor you need to survey both halves, but not necessarily disclose all information that some might consider a "freeSurvey" on your map. If corners were set in the past, you would be locating at least 6 markers. Easiest way to show is broken line "ties" to the corners on the right parcel. In many cases no markers were set and the only monuments you have are the houses themselves. Then it is necessary to show the entire building and the splits from the corners. There are times when you find that both halves of a double were not built at the same time. Let us assume that your PQ side was constructed first, the common wall could be entirely on the left lot. When the right half was erected they built to the face. The center of the common wall does not become a new lot line, but in essence the dwelling to the right has marginally more interior area. Were the left house to be demolished the entire common wall on that side would have to remain as support for the right dwelling. One should be able to obtain permission to enter the right welling yard are to do the survey, but that is not always the case. It is not uncommon to run a survey line through the dwelling. In the majority of cases one can reliably hold the splits, occasionally a common wall may be off angle to the lot line. In that case you give some left and right offsets but you do not use such words as "encroachment". As long as the line is within the wall +/- 0.10' there is no need to consider any type of lot line adjustment/agreement.
A few years ago I surveyed an entire block for one single family dwelling, 2 doubles to the East and row houses to the West. The most adjacent double split to the East was more than a foot off the lot line, but since it had been erected before the map was filed it was shown out of place on the filed map, but did not affect the lot lines for any other purpose.
Paul in PA
As the op is only surveying for a year and is based in the UK I would say he hasn't a clue what you are going on about.
For the op the simple answer is as Peter said, to tie into a building corner or some common point. Personally I would start and finish on a gps point or else traverse back the way you came.
I believe that the UK is similar to Mexico... Occupation is superior to the land net. I see this type of survey more often than not, it serves the purpose well.
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If you insist on a closed loop?ÿ ?ÿyou could?ÿ set 2 tacks on each hub?ÿ and have along skinny closed loop about 0.06'?ÿ wide
Thanks for the replies guys.
For the purposes of this survey its not necessary to survey the adjoining property. This client has to have a topo done of their land in order to get permission for an extension (addition to their house).
From my understanding of your suggestions to perform an open traverse I think I need to do the following. I'll use the diagram below as an example. I'd be grateful if you could let me know whether I'm catching your drift or not.
1?ÿ?ÿ Occupy STN1. Backsight CHECK1, foresight STN2. CHECK1 can be a prism on a tripod. Do detail survey.
2?ÿ Occupy STN2. Backsight STN1. Shoot CHECK1 as a check for blunders. Foresight STN3, foresight CHECK2. CHECK2 can be a prism on a?ÿ?ÿ tripod. Do detail survey.
3?ÿ Occupy STN3. Backsight STN2. Shoot CHECK 2 as a check for blunders. Do detail survey.
In the example given I've used two different check stations but I could use one check station if it can be seen from all three traverse stations.
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Good points and good options having been made, a couple of things to add:
in your alternative above (using tripod mounted prisms for your checks), go ahead and set them over nails. You never know when you??ll be back and that??s 2 more chances ?ÿyou??ll already have control ?ÿestablished when you get back that way.?ÿ
Keep on top of your jurisdictional reg??s/ Board rules. I remember some craziness from the early nineties where SC (US State) began requiring a formal closing angle for any boundary traverse. This was largely understood to require three separate and unique physical setups on the smallest boundary. May have gone the way of the dodo, I left SC before i became licensed. But, felt it is worth noting.?ÿ
Think in terms of redundancy rather than dogmatically closing traverses.?ÿ Closed figures are very desirable, indeed, but there are other ways to skin this cat.?ÿ After all, if you are going to insist on closing all traverses what are you going to do when you get your hands on RTK??ÿ?ÿ
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Think in terms of redundancy rather than dogmatically closing traverses.?ÿ Closed figures are very desirable, indeed, but there are other ways to skin this cat.?ÿ After all, if you are going to insist on closing all traverses what are you going to do when you get your hands on RTK??ÿ?ÿ
I can't remember the last time I closed a traverse.?ÿ Redundancy (double tie from independent locations) has been my sop.?ÿ Same for gps, shoot 'em twice.
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I can't remember the last time I closed a traverse.?ÿ Redundancy (double tie from independent locations) has been my sop.?ÿ Same for gps, shoot 'em twice.
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True corner - could you expand on what you mean please by "double tie from independent locations" instead of closing a traverse. I think we use different terms this side of the pond.
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a diagram of "forming a double tie from independent locations" would be really cool. I have trouble visualizing from words.
Cheers, Andrew
A double tie is the same as your check points, but are to other important points that need to be located.?ÿ The same point is located from different station points.
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Ed
thanks for you help guys
did an open traverse today. I used the corners of a house as checks from successive stations. How much agreement in x,y,z for double tied points from different stations is desirable for an open traverse??ÿ
Cheers, Andrew
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Depends what you're doing.?ÿ Boundary survey, I'd want to have a tie at least 0.02-03', or less.?ÿ Topo, you could allow a bit more H error, but would like to have the V about 0.05' or less.
I'm sure there are some here who'd demand it tighter, and maybe adjust everything.?ÿ But as the cow said, we're surveying, not building a precision timepiece.
