Avoiding mistakes when not traversing?

If you do a topo, and the map includes the two stations, and their physical descriptions as well as the bearing or azimuth you assumed between the two (and distance), then that is your baseline. Why do you need an additional closure?

That said, always check in and/or close a traverse. Even if you simply shoot a common point from each station as a check.

With only 2 control points, and no connection to a grid system, you risk -if just one of the control points gets lost, damaged, or even occluded - lost losing any ability to jump back onto your control to do a stakeout after design. I really like to have at least 3 control points for even the smallest of jobs.?ÿ

I do have GPS, so I'll touch them with that, then measure the angles and distances with the total station, and pour both into a StarNet adjustment. This adjustment process takes a very few minutes if everything is good. If it's bolloxed up then whatever time I spend fixing it is worth it.?ÿ?ÿ

For each setup of the instrument, the first and last "topo" shot is on a known control point, and somewhere in the set will be a shot on a third point with known coordinates. This is commonly known as the "third point check". This can be:

• the first "topo" shot is on the backsight, the final shot is on another control point. (most common)
• the first and last "topo" shot is on the backsight, with some other shot in the middle of the set on another control point.
• the first shot on some known point other than the backsight, the last on still another known point - and so on...?ÿ ?ÿ

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Naturally, this practice means that I need to have at least 3 control points.?ÿ ?ÿ?ÿ

@norman-oklahoma I do outbound and topo surveys on average lot sizes of one acre for urban home demolition, subdivision and reconstruction and strongly agree with you.?ÿ I set the law down for my crews 5 or 6 years ago, no matter what surveys we are doing, small ones like 1 acre to much larger ones, always set as many points that will remain, outside of the project limits so that when points get obliterated there are always back up points on the same grid system, whether it be local or State Plane, to fall back on without recreating the wheel.?ÿ I do a ton of large commercial surveys where the envelopes are pushed as to what will legally fit in and losing points is an every day thing.?ÿ My crews report back to me on what points were lost and what new points were set so that I can keep job control files current and update control sheets.?ÿ It's quite a task for me with 5 crews but well worth the time to be on top of it while new work set up is crushing down.

@norman-oklahoma

Norman thanks for your reply. I'd be grateful if you could expand on what errors it guards against, errors in setting up control, or errors in detail pole height or prism constant selection.

I've thought about using this technique before, but normally tripod legs are in the way.

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@fobos8

First, lets define some terms. There are errors, and then there are blunders. Errors you (mostly) live with, blunders must be trapped and fixed.?ÿ

It's OK if tripod legs are on the way. Tripods are for carrying targets as well. You can shoot the target on the tripod as a topo shot. That's OK. Just account for the measure up. OR - finish your control work, put the tripods back in the truck (van? lorry? ute?) and proceed with topo.

The most common mistakes are measure up errors. The second most common is getting your point numbering crossed up. Third would be getting onto a monument (nail?) that isn't yours, but is nearby enough to be mistaken for it.?ÿ This third point checking will reveal an error of any of those type. First, it provides elevations on shots to compare with elevations on the control. The only way you get a match is if both the control and the topo shots are correct. In a similar manner, the horizontal coordinates of the check shots you include in your topo data set must nearly equal the control coordinates you determined for them. Again, for that to happen both your control work and your topo work must be correct. And both instrument point and backsight must be on the intended points.?ÿ So you collect these check points in your topo, compare them to the control coordinates you determined by other means, and when they substantially agree you can be pretty sure that you haven't made a blunder.?ÿ ?ÿ

BTW - double angles on control work and boundary monuments.

So... your work flow goes like this..... arrive on site, determine suitable locations for 3 or more control marks ...... set your monuments ..... Set up on one (typically the middle one) and turn a set of angles and distances between backsight and foresight.?ÿ Now you have coordinates on 3 control points.?ÿ Tie whatever boundary marks you need to, IMO it is preferable to do this by sets of angles/distances as well. Now, put the backsight and foresight tripods away. Reset your instrument backsight with your topo rod on the backsight. Then record your first topo point on the backsight point, coding it "CHECK" or something similar. Confirm that the coordinate you just recorded is substantially the same as the corresponding control point coordinate. Proceed to collect your topo as needed.?ÿ When you have done all you can from that intrument position, complete the topo collection with a shot on the other control point. Code that last point "CHECK", or whatever pleases you. If necessary, set up over one of the other control points and repeat the procedure as you continue collecting data.?ÿ

One more thing - If you are set up for a long time on a control point while collecting topo data it is a good idea to maybe get one of these third point check shots every so often. Maybe every hour or so? Maybe every hundred shots or so? It sometimes happens that your initial check shot is good but the end one isn't. That means the instrument got bumped (or something) somewhere along the way, and the data collected after the bump will be suspect.?ÿ If that happens you will hope to have some means to isolate the error and mitigate the damage.?ÿ ?ÿ

@norman-oklahoma

If I'm reading some of your procedures correctly, the software some of us use makes some of those things easier.....

I can use "check point" to shoot a check on a third point which shows in the raw data but doesn't store an extra unneeded point. We were ending up with like 10+ points on some control because of all the frequent checks.?ÿ

I can use check backsight to shoot an angle to the backsight proving my set-up was still good with raw data but not using up another point number also.?ÿ

Creating linework as you go and keeping an eye on the screen to make sure things look right is also a good idea IMO.?ÿ

@350rocketmike

I'm aware of those functions, most data collection has something along those lines. I still like to have those check shots packaged up with the topo raw data. I frequently re-run the raw data in the office - perhaps after adjusting the control - and those points serve as QC in that process. I appreciate a field guy who will keep an eye on things but I also need stuff in the data set that will prove, if necessary to a third party reviewer, that an eye was kept on things, perhaps months and years after the fact. ?ÿ

The check points get sorted off to a discrete layer in the CAD drawing (via field to finish) which is simply turned off most of the time and gives me no trouble.?ÿ?ÿ

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@norman-oklahoma

Suppose I number the three control points 1, 2, & 3. And my topo collection starts with 10000 (which is my typical way of doing things). Then the first third point check shot will be point number 10000. Say, the topo data set runs up to 10251. Then the point number of the closing third point check will be 10252. And these check shots get coded with a?ÿ

Specifically, I do not number these check point shots 1, 2, or 3.?ÿ I'm not sure why, but this has been a point of confusion for field staff.?ÿ

If I'm running control which is going to get resolved and adjusted back at the office it is quite acceptable to number the shots on control as their actual number. Because control and topo is different and gets treated differently in the office. As a rule of thumb - if you are shooting things with a single one-faced shot it gets a unique topo point number. If you are doubling angles to a point it gets numbered with the point number you first gave it the first time you tied it.?ÿ ?ÿ ?ÿ ?ÿ ?ÿ

Posted by: @mark-mayer

Specifically, I do not number these check point shots 1, 2, or 3.?ÿ I'm not sure why, but this has been a point of confusion for field staff.

99% of the time it's poor understanding of, and/or training for, the field software package(s). Field crews seem to think that every single time they observe a point it will "change it" somehow.

Which is weird, because when software literally gives you the option of "store as a check" or "overwrite" or "average", which of those do you think is going to affect the current position of the point? It sure as heck isn't the first one...it's right there in plain text on the screen.

Personally, if a point has been defined, adjusted, or otherwise set, I'm storing the point as its actual number/name, and storing a check shot. Makes post-processing and QA/QC far easier, since I don't need to perform inverses between each one and the control/adjusted value. I just run a point derivation report with defined tolerances, and anything outside of those tolerances gets flagged.

If there are flags, I know exactly which observation/check it was, and can then hunt down any possible blunders.

But when I have crews shooting in point 101 as 101A, CK101, 101-2, 10453, 101chk, or whatever happens to come into their minds at the time of observation, it makes it far more difficult to perform office processing. Multiply that by ten, twenty, fifty different control points and/or monuments, and it gets downright ugly trying to merge everything so we can review.

@norman-oklahoma

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Thanks Norman

Up till now I always leave my backsight and foresight tripod up after shooting the control. I regularly check into the backsight if there's kids around, its windy, sunny or my face has been pressed up against the scope. If the backsight check shot has a discrepancy I check the foresight too.

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I understand the reason for your method of breaking down and then setting up again but wonder if there's a more efficient way of working?

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Regards, Andrew

@mark-mayer

I think the problem is our office staff doesn't have the time to sit down and deal with all those extra points when I'm doing maybe 5-10 different jobs a day with who knows how many check shots.?ÿ

We bought out another company and the "check point" method is the way they've been doing it for a while apparently, so I just picked that up from them.?ÿ

Some of our subdivisions just keep getting bigger and bigger to the point that the office computers can barely handle exporting an upload. It also makes it hard to pick the point off the screen when there is 10+ "CHK" shots hiding the original control point in the point clusters.?ÿ

Posted by: @mark-mayer

The check points get sorted off to a discrete layer in the CAD drawing (via field to finish) which is simply turned off most of the time and gives me no trouble.

Automatically. ?ÿNo fuss. ?ÿNo muss.

@brad-ott

Maybe I'm weird, but I like my drawings clean, and don't want any check points in my drawing files, even though ours are automatically sorted onto a no-plot/frozen layer if some happen to make it through the review process.

Our workflow has all QC occurring during post-processing, so there's no reason to be inversing check shots in CAD. Search points, calcs for construction, anything that is not a final/adjusted value for an observed entity in the field all reside in a separate drawing or drawings.

If it doesn't actually exist and wasn't observed, I don't want it in my topo or boundary CAD files...but I can see how if a surveyor is not using post-processing software it would be useful to keep them there.

@fobos8

I've described a work flow in that way to illustrate the point that collecting control is one set of tasks, collecting topo is another, and you should regard them as such. If you choose to leave the tripods up and to use them that is OK, it's more in where your mind is at while doing so.?ÿ?ÿ

@350rocketmike

Hmmmm ... so you say that your office staff doesn't have time to do routine QC functions? Oh, great.?ÿ

I gather that you are doing a lot of stakeout work. A lot of time with that sort of work the structure is built before you can get back to the office with as staked recorded shots. So there is no real push to check the data ..... UNTIL ..... one day, maybe weeks or months in the future .... a problem with the location of the works is discovered and the finger pointing goes immediately back to the stakeout and the surveyor. THEN you really need to be able to pull out that one as-staked file and PROVE that you did your part of the work correctly.?ÿ

You can do staking work for a thousand days and have your profit for the whole lot wiped out because of a single mistake on the thousand and first day. I record the check shots and the as-staked shots and?ÿ archive the file religiously. I rarely do anything more except for the few occasions when something has been questioned. I've had my ass saved more than once because I could produce that check shot data and show that my work was true.

So I record the checks and I archive the data. In a great majority cases for staking work, that is as far as it goes.?ÿ

For topo and boundary work a great deal more time might will spent in the office, the time spent reviewing check shots being a trivial part of the whole. You code the check shots, F2f sorts those points to a dedicated layer, you check, you turn off the layer, and move on with certainty.?ÿ

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@norman-oklahoma

Yes, I'm not saying it's right, but I have to he absolutely sure I've done the job right before I leave. Often times they're forming it before I leave the site and poured before I finish the next job.

So you're saying the raw data showing the check won't suffice the same as shooting the point? With the number of lots we're laying out the check points add up really fast. They are also shown on my notes.?ÿ

@rover83

Pulling them into CAD is an easy way to compare them to the control. Zoom in on the control point and make a selection set.

I do not like to include the check shots in a deliverable. No need to show the client how the sausage is made. There are various workflows to achieve that.?ÿ Fodder for a whole 'nother set of postings.?ÿ?ÿ

@rover83?ÿ

You guys need another field operator who is moving towards license?

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@350rocketmike

It probably will show it. Confirm that for your self, with your particular software. It may be a bit more obscure. Remember, if the stuff really hits the fan people who don't really understand what you do will need to be convinced, and may not have software that can read your raw data format. With that in mind a readable plain text ascii Notepad readable file format is a good thing.

What I have described is by no means the only right way to?ÿ do it, but it is how I have been rolling since 1993 through a succession of raw data formats.?ÿ Heaven only knows what the next 25 years will bring, but I'm pretty sure that my system will survive it.?ÿ ?ÿ