Being from Europe, is it true that you guys still use Angle Only on a regular basis? I heard that this was the case in a video somewhere that alluded to legacy control in the form of church steeples and the like but have been skeptical.
If three is the minimum then what is the maximum?
I have done quite a lot of Monitoring off of two, mixing configurations and shooting from different directions into the area of subsidence and achieving results well within the error budget. I know this sounds like heresy and would not be possible without expert level network development but it has been my experience. I have not been the guy reducing the network but I have been the one measuring the points and reducing the monitor so I know there is not optimization or funny business post control.
The super structure and building guys do like to shoot lot of points though, part of that seems to be related to ever diminishing line of sight and works almost as an system of local control networks inside their respective areas of concern.?ÿ
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No we are quite with the times!
Must have been something about mapping before EDM?
I did see it done once in Australia because his instrument did not have free-station program on it. The older model TC400 as I recall. Leica obviously thought it was an option that should be paid for. (like reference line).
I had very little confidence in it. I suppose if you resected from 3 far away stations and checked on to a 4th one nearby you could have a little confidence.
Have used up to 8 or 9 observations in a free-station, with retros it can be easy enough to have them in place. And if one moves drastically it is easy to spot.
Current sites don;t have good places for stable retros so I have a few good quality stations (pillars) and tie them to the control network in a tight network. Typically 4 round each bridge, so should be possible to sight 3 from most positions. I would even use 2 if I had to. It all depends on how confident you are in the stability of the control, and also the stability of?ÿ your setup (tripod etc;).?ÿIf I had just done a 3 or 4 point resection and all was perfect I would have less worries.
Jim Frame
Thanks for the info on this thread. You have me re-thinking things here.?ÿ
I sometimes do resections off record calcs just to get things started w/ a boundary and be able to find more points that day, I'm wondering if these principles you are talking about would apply to situations where you are not using your own control but fitting onto things that have quite a bit more slop.?ÿ
Some have mentioned here that the angles make no difference, but this doesn't seem entirely right because if you had a really small angles between 2 points, say 10 degrees, I wouldn't think this would produce a very good result.?ÿ
Might be might be from my engineering background but I tend to visualise it like a 2D structure.
eg if you represented your control points as bolts or pins fixed to a board
then your observations from the instrument to?ÿthe control points and the point being measured to could be represented as meccano strips. (maybe there's other names for the old construction toy).
and the errors would be represented by the holes in the meccano being bigger than the pins (centring error), or slotted lengthwise (distance error). Angular errors would be represented as slip at the meccano joint representing the instrument (bolt not tight enough)?ÿ
so you can imagine how much waggle (technical term) there would be at the instrument point, and also the point being measured from the slop in different arrangements.
I also think of it like a group of CAD lines being rotated to fit new points.
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- Don't resection points in the same quadrant.
- Do direct?ÿand?ÿreverse shots in the resection.
- After the resection is stored, do a new setup on the resection point. Backsight the furthest point. Foresight check the closer point(s).
It's a great tool. Like others have said, just check your work.
Hi,
I always made sure they were able to visualize it..
It helps if you think of it as a stone hanging on some wires.
So if the instrument is the stone.. and the observations are the wires to that stone... will the stone move when you try to push it?
In which direction would you need to attach another wire to make it more sturdy?
Personally I always believe that a lot of "rules" and fictive numbers don't make a lot of sense if they do not fully understand it.
It's not hard to get "good" values... but it can be hard to get "realistic" values...
Greetz,
Floris.
- Don't resection points in the same quadrant.
- Do direct?ÿand?ÿreverse shots in the resection.
- After the resection is stored, do a new setup on the resection point. Backsight the furthest point. Foresight check the closer point(s).
It's a great tool. Like others have said, just check your work.
Point 2?ÿ I absolutely agree with. Points 3, I (usually) shoot the furthest point I'm going to use first, that makes it set to zero angle. But I don't know that it really makes any difference to the solution.?ÿ
Point 1, I don't understand your meaning. Please elaborate.
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Personally I always believe that a lot of "rules" and fictive numbers don't make a lot of sense if they do not fully understand it.
The unfortunate fact is that not all field crew have a full conceptual understanding of what they are doing, or even seek to. In order to proceed with the material at hand we sometimes have to have some rules that can be applied. Not everyone can be trusted with "use your best judgement" as instructions.?ÿ ?ÿ
I refer you to my signature line, below....
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- Don't resection points in the same quadrant.
- Do direct?ÿand?ÿreverse shots in the resection.
- After the resection is stored, do a new setup on the resection point. Backsight the furthest point. Foresight check the closer point(s).
It's a great tool. Like others have said, just check your work.
Point 2?ÿ I absolutely agree with. Points 3, I (usually) shoot the furthest point I'm going to use first, that makes it set to zero angle. But I don't know that it really makes any difference to the solution.?ÿ
Point 1, I don't understand your meaning. Please elaborate.
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My guess is he means don't have all you control points within 90 degrees of each other, for example all N-E of your setup.
I've violated this rule with the scanner. After registration everything matches.?ÿ After setting up control and running everything I go over to an area and think I really should do a setup here.?ÿ So I free-station it instead of resetting up on a control point to throw a fly point (some call it a work point) over there.?ÿ I like to have three control points in view.?ÿ This is how scan registration was traditionally done before it became convenient to run it more like a total station.
- Don't resection points in the same quadrant.
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Small angle between points could be ok if you're not far away from one of them.
Like when your control point is in the bushes and you can't set up on it.
This is what I'm thinking - If the site was clear, no obstructions, would you set up and backsight the control you propose to resect to, and stake out the resection point? If the answer is yes then, maybe, you are good to go with the resection geometry.?ÿ ?ÿ?ÿ
People don't like resection because can't see the errors in it , unless is all arbitrary.
Trav adj. = pnt positions with errors. Residuals are good. Client is happy, lets say????.
Site job:
Resection from this trav (Resection by cords only!)=?ÿ
Errors in distance due to adjusted cords.
-Need to check every trilateration , if OK keep going.-
How can u get over the problem of the adjusted trav, have a confidence in your resection and carry out ur job?
1) fake resection- normal set up: Arbitrary.
Set up PNT 0,0,0?ÿ
Shoot BS azimuth 0 00 00?ø.
FS next station.
2) real resection with the same Stations, after u have resolved the triangle.
You know:
- Azimuth trav STNs ( from G_cords )
-Distance of same trav STNs from arbitrary, this time.
-Distance trav STNs from arbitrary PNT.
- Internal angle in P.
Compute trilateration errors, give cords to PNT and Smash it.
Side shot:
Use trav STN cords (Fix) and stick instrument on top. TBM.
BS dist and azimuth trav STN ( Free ) , accept.?ÿ
Instrum is orientated.
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First thing i do is READ the manual and understand the math behind what and how it does a resection or free station. Trimble Access actually has two different main mathmajical formulas that it uses depending on user choosing and number of pionts and if hz and vt is used. From that you can build the field procedures.?ÿ
A trick I use when I am limited to two points. Is once resection is done re do a station set up but bs the fs and do a check. I know this is old fashioned and was a field procedure some used when we computed them longhand. Kinda helped make sure you were not reversing a bearing or azimuth etc. ?ÿi like around 30 to 55 degrees geometry depends on what I am doing. And which method. Jim made some very good ?ÿpoints and it shows he has checked the math. I still see companies refusing to allow resections because of the past issues. ?ÿAnother field ck is once completed have them set a temp point randomly where it can see two of the main points or a third point of overall traverse. At some point the either occupy it and ck to something not used or occupy something not used and turn to that point.?ÿ
dont know what software but not all software uses the same math to get to the position. So that will dictate your field procedures. ?ÿGood luck. ?ÿ
A very interesting topic.
Resection is very useful in construction conditions because it saves time and reduces errors associated with positioning successive stations, and increases accuracy due to the absence of station errors.
Colleagues wrote very important and interesting things.
For my part, I would like to add that in the case of construction sites, it is hard to get the geometry of the setting due to the possibility of preserving the view.
There are problems with the geometry of the distance, some points are closer, some are further away, this affects the accuracy. In the case of high-rise buildings where the points from the laser plummet are close, it is worth adding an angle to another, one further point.
Many points do not mean better, the geometry is important. Having an angle and a distance makes it easier, but you can't help but have an idea of how math works. Three points spread out about 120 were taught in school, but in construction conditions it's hard to keep them, I'll count with ellipses what Jim Frame wrote about, because it's very practical.
A trick I use when I am limited to two points.
My trick is such situations is to set up on one, backsight the other, and spin in a new point.?ÿ The rule is 3 points used in resections. Period. No tricks.
