Here is a quick sketch of what you are talking about I think, feel free to correct me if I am wrong.
Obviously you can not see directly from station 1 to station 2. Instead do several sets of measurements to points A and B from both stations and use a least squares adjustment to tie it all together. It is good to get other visible reliable points that you can see from both stations as ideally you want more than 2 points.
Use something pretty solid for points A and B such as spikes works pretty well.
...How much agreement in x,y,z for double tied points from different stations is desirable for an open traverse??ÿ
About the same amount as what would be considered good closure if the traverse were a closed loop. Taking into account just how sharply defined, and therefore repeatable, your check-in points are.?ÿ ?ÿ
When you run your closed loop traverses you follow a certain procedure. You use this for a backsight and that for a foresight. You set up the?ÿ instrument on such and such a tripod and turn so many sets of angles, blah, blah, etc., etc.. And, if you do your work without blunder, you achieve a closure within a predictable range. If you run an open traverse in the same manner, following the same procedures, and presuming the work is blunder free, your points will be equally precise. The check-ins are to detect blunders, which are commonly of large magnitude. So the checks are either pass or fail. There is no in between.?ÿ
Great advise Norman - thanks
I did my first open traverse yesterday and shot some common check points from the stations. I was disappointed with the results - the northings and eastings varied by up to 12mm (0.04'). The levels were good.?ÿ My closed traverses normally close within a 5mm (0.02').
I was using a Trimble MT1000 360 prims at a height of 5ft for the check shots which is not famed for its accuracy. I wonder if I should be used a Leica round peanut prism mounted 1 foot from the ground? This should give more consistent results.
I would also say also measure the inside. I can think of a few times in Florida where someone bought two units and changed the interior walls. Later filled in the openings and sold them. I knew a lot of surveyors that never went inside on condo surveys.
I wonder if I should be used a Leica round peanut prism mounted 1 foot from the ground? This should give more consistent results.
Rather than trying to shoot corners put a small pencil mark on the wall and shoot it relectorless. It may be that the repeatability of shooting a building corner is your bugaboo here.?ÿ
FYI - when tying buildings,?ÿ I shoot the wall faces reflectorless, then intersect the wall lines to generate the corners. I believe I get much more accurate results that way, and quicker.?ÿ ?ÿ
Your right - I am scared of shooting building corners reflectorless and using it as control. I've had some dodgy results shooting reflectorless in the past so I make sure I shoot loads of points nowadays in case some are dodgy.
Having said that though your idea of making a pencil mark and shooting it reflectorless could the best solution for control on open traverses so I will try it again.
Many thanks, Andrew
These targets have really helped in creating check points.
when doing an open traverse how many common check points should be shot/established per station setup?
?ÿ
Whatever your experience tells you is adequate for the situation. ?ÿHow much better is seven compared to two?
There is an ancient saying used by carpenters: ?ÿMeasure twice, cut once.
What bothers me is that we tend to lose sight of reality when we have readouts to several decimal places. When locating a house on a tract, what is the truth others are seeking. ?ÿBasically, why do they care what your presentation of data provides? ?ÿIs it totally on the tract? ?ÿDoes it not cross easement and setback lines? ?ÿPrecisely where is Structure A relative to Structure B so that some connecting link can be designed?
Where are the shots taken? ?ÿAt the structure/ground footprint? At the siding corners? ?ÿIs the wall actually vertical? ?ÿDo you consider projections such as window sills? ?ÿAt the eave corners? ?ÿWHAT DOES THE CLIENT NEED TO KNOW AND WITH WHAT ACCURACY? ?ÿIf you don't know the answer to that question, stop doing anything until you do. ?ÿAll the careful surveying practices and computerized number crunching mean very little to a client who is going to use an axe to cut at the spot that was located with a micrometer. ?ÿLaugh, but an example of that appeared on here yesterday where 500 random locations were to be pointed out to a backhoe operator so he could dig and replace a small patch of soil so as to reduce soil compaction in the planned root zone for trees to be planted.
Thanks for your reply Holy Cow. Unfortunately I don't have much experience of surveying yet so I was wondering how many check points others use per station setup when doing an open traverse.
My gut says one check shot isn't enough and to do two for each station setup?
@ fobos8
My mentors ask that for every hub location to have at least 3 nearby objects reference by angle and measured distance and to make at least one traversed tie across the middle of the property.
With GPS, observations at beginning and end of a TS traverse will do the trick.
On critical properties, I place targets that can be seen from all directions,many on posts and signs on adjoining property.
It makes it very easy to check my work and to be able to do free station setup when my hubs have disappeared.
Thanks for your reply Holy Cow. Unfortunately I don't have much experience of surveying yet so I was wondering how many check points others use per station setup when doing an open traverse.
My gut says one check shot isn't enough and to do two for each station setup?
One is enough IMHO. In addition, of course, to the foresight and backsight points of your open traverse. BTW, once the veracity of the control points has been proven, there is no need to continue to tie points other than your for control for checks. But I always demand a shot on the backsight be recorded, and a check shot to another known point be recorded as part of every boundary and topo data setup.?ÿ ?ÿ
That's great guys - thanks a million.
Should I be able to determine traverse accuracy ( 1 in xx,000) if I perform check ties on an open traverse. Should least squares work?
