Is there any situation where a traverse adjustment would not be necessary? For example a topo of a 1 acre site with 5-6 setups and a closure of 1:20000+. Is it really necessary to adjust such a survey? Just curious what other peoples opinion on this is.
If adjusted what would be the preferred method?
> Is there any situation where a traverse adjustment would not be necessary?
Sure. I would venture that more people would not adjust such a traverse than would.
I would, using StarNet. It's not to somehow improve the result. It's to provide a paper trail proving what the result was. Properly collected such an adjustment would take 10 minutes, tops.
The only reason is if you were to setup on your closing point and backsite the last point in your traverse. In the example you gave it probably wouldn't matter but say its a longer traverse and the actual closure error is 0.30'. If you setup and backsite that last leg of the traverse, all the error is at that setup and if you were to say set property corners from that setup, the error would show up.
Hope that made sense.
> ... Properly collected such an adjustment would take 10 minutes, tops.
And, I might add, if improperly collected it needs me to spend whatever time is necessary to get it right, doesn't it?
Adjustment provides a mathematically consistent set of data. Better that it compute out exactly, even though we know it isn't really perfect.
You don't know where the error is, but that 0.04 probably isn't all in the last leg, so better have several points moved a little. That will, on average of all cases, make the rms of the actual (unknown) errors smaller.
Least squares works great for this and handles whatever redundancy you have (did you set up on the last point?), but if you don't have significant redundancy, then compass rule is probably almost as good.
For me, it's more about the actual misclose distance. If it's less than 0.1', forget it. I feel that you have to adjust if it's more than that because you'll basically be forcing a closure on the boundary if you don't.
When it is convenient and does not take away from the task at hand, yes.
I always do an angle closure adjustment first on a traverse and that will just about fix most closures when the adjustment is less than the amount of your instrument's potential per setup. For the 5sec TS the adjustment is rarely over 3sec per setup.
The Carlson Surveyor1 Cogo program I've used since 1983 will also do a vertical adjustment.
I will give deed plots a Crandall adjustment so there will not be two points 0.002ft apart.
Most of todays traverses are open ended and starting from and closing into GPS control points at each end.
Most of the closures I make are done on the data collector. I download the original file to filename.asc, make closure adjustments and download those results to filename_adj.asc
There are many parcels that I do not adjust when the coords are still on top of the hubs.
😉
> > ... Properly collected such an adjustment would take 10 minutes, tops.
> And, I might add, if improperly collected it needs me to spend whatever time is necessary to get it right, doesn't it?
Yeah, that's the major value in collecting and adjusting observations: for the purposes of quality control. That means looking at relative uncertainties in the positions of things, including elevation uncertainties and it means examining results and documenting them. The time required is quite minimal and the results are always worth the effort.
Most small jobs i do the closure is lass than 0.1 and angle
Closure is on seconds. So adjusting the traverse might only
Change each setup 1-3 seconds and this would result in moving
These points thousandths of a foot. I personally do not spend
The time for something so minute. That's just me.
I dont believe in adjusting construction layout. If your closure error is greater than what you can tolerate then re run it. This comes from working on projects in Florida where you don't have much elev. to play with. You don't want to introduce a few hundreths here and there when the real error is in one setup and now your staking stuff up hill.
> Is there any situation where a traverse adjustment would not be necessary? For example a topo of a 1 acre site with 5-6 setups and a closure of 1:20000+. Is it really necessary to adjust such a survey? Just curious what other peoples opinion on this is.
>
> If adjusted what would be the preferred method?
It is common for us to close our small traverses with .01' Horizontal and Vertical distance check, with closing angles less than 5". Unless there were cross ties, the value in adjusting each control point by a couple of thousandths seems very small. If it is an ALTA, where you are certifying to a certain error ellipse, that is different.
Now...for a legacy project (one I expect to visit multiple times, at various stages of development) I always create and maintain a StarNet file, simply because as control is added in, it provides a means of incorporating new traverses, and seeing how the play with previous control. I do this regardless of raw checks and closures.
Preferred method is StarNet, using their conversion software to convert Raw Data to their format.
Don,
When I think of Least Squares, I think in terms of 'analysis and adjustment'. While I agree with the thought that adjusting points less than the frost heave between site visits is generally useless I consider the quality control of my data paramount. Nothing gets published with my name on it without full QC. Data doesn't even go to drafting without being checked. It saves repeat work and embarrassment. When I can run least squares and quantify my results in just a few minutes I see no reason not to. It's very cheap insurance...
Tom
I agree with this as well. If I'm going to send some data out with my name and number on it, I want to feel confident that I crossed my I's and dotted my T's (or something like that).
The biggest hurdle I get is when one of my field crews comes in with the initial data (GPS or conventional) and I go through the effort to review and adjust the data, but then, they fail to put the new control data in the controller.
I had a party chief tell me once that it took too much time to redo the calibration onsite and so he just used his original control for everything and asked that any calculated points for staking or setting monuments be adjusted to his control.
I had a few choice words for him after that exchange of words.