Survey Control Methods

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smacl
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Re: Survey Control Methods

Post by smacl »

jcoco3 wrote: Fri Feb 04, 2022 12:58 pm Thanks for the information guys, glad I am not the only one that cares about these minuscule or obscure details. I think it is the type of knowledge that makes the "guys behind the instrument" truly skilled (not that I would ever claim to be one of them). I agree turning rounds helps, and it is pretty common for the surveyors I have met to use 2-5 turns on robots for shooting targets. Not sure it is a consistent practice how turning rounds compares with a collinear design, but my hunch is that the collinear design probably eliminates the majority of the problem. That Leica white paper information is just the type of peace of mind information I come here for, so thank you for that :D Puts my mind at ease a bit knowing that some manufacturers appear to be phasing out the non-collinear beam design.
Co-linear EDM and telescope optics help solve some but not all errors relating to collimation. Correct instrument setup and calibration also play an important role. A single measurement from an excellent instrument that is out of calibration, not plumbed properly over the point, or off level will still give you a bad result while saying everything is fine. Taking measurements on both faces and transiting the telescope is still beneficial. Where you're sighting multiple targets, surveying rounds in order is also very important. e.g. if I'm on station A, sighting B, C and D, good practice is to observe B,C,D on face 1 followed by D,C,B on face 2, ideally repeating three times if you're looking for best accuracy. Surprising the number of novice surveyors that forget that you need to sight two targets to measure a single angle with a theodolite and lose the value of repeated measurements by sighting the same point multiple times without re-observing the backsight.
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Re: Survey Control Methods

Post by gsisman »

smacl wrote: Fri Feb 04, 2022 1:38 pm
jcoco3 wrote: Fri Feb 04, 2022 12:58 pm Thanks for the information guys, glad I am not the only one that cares about these minuscule or obscure details. I think it is the type of knowledge that makes the "guys behind the instrument" truly skilled (not that I would ever claim to be one of them). I agree turning rounds helps, and it is pretty common for the surveyors I have met to use 2-5 turns on robots for shooting targets. Not sure it is a consistent practice how turning rounds compares with a collinear design, but my hunch is that the collinear design probably eliminates the majority of the problem. That Leica white paper information is just the type of peace of mind information I come here for, so thank you for that :D Puts my mind at ease a bit knowing that some manufacturers appear to be phasing out the non-collinear beam design.
Co-linear EDM and telescope optics help solve some but not all errors relating to collimation. Correct instrument setup and calibration also play an important role. A single measurement from an excellent instrument that is out of calibration, not plumbed properly over the point, or off level will still give you a bad result while saying everything is fine. Taking measurements on both faces and transiting the telescope is still beneficial. Where you're sighting multiple targets, surveying rounds in order is also very important. e.g. if I'm on station A, sighting B, C and D, good practice is to observe B,C,D on face 1 followed by D,C,B on face 2, ideally repeating three times if you're looking for best accuracy. Surprising the number of novice surveyors that forget that you need to sight two targets to measure a single angle with a theodolite and lose the value of repeated measurements by sighting the same point multiple times without re-observing the backsight.
Absolutely Shane.
I had a party chief a few years back who would backsite once and then turn multiple times with Direct and reverse on a fore-site (property evidence) but never return sight to the backsight. SO I ended up with a VERY accurate vertical elevation on a Property corner that I wanted a VERY accurate horizontal position.
The new robotics and field collection software make it a no-brainer for incorporating mandatory sets for traversing, Flypts and Critical Property evidence. Especially if you have auto-targeting and or Auto-Calibration (more and electronic-digital internal calculation now days with all the software on board and not a manual adjustment of the cross hairs like in the old days).
I very rarely get out to a site when the guys are actually recording the info so our "Survey Procedures Manual" describes what is the standard required procedure for Crew Chief to institute for different type of scenarios. After all it is MY seal that is going on the work. Every Surveyor who seals work should require his crews to perform field work in the way that he is comfortable signing off on. The U.S is such a highly litigous nation and some urban areas even more so (DC area and surrounding is one of them.)
With the high-tech stuff that is out now (military Grade IMU tilt in RTK sensors and other items (Auto-measure HI lasers, etc.)Auto-Calibration software-firmware-it has helped to reduce human error and bad procedure in the field (where like you say most errors generate). It helps when the pool of skill field operators gets smaller and smaller and you have to have guys with less experience or who haven't come up under some hands on tutelage in the field, having to run a crew. Many times I went out in the field just to watch my guys procedures to make sure they weren't cutting corners. Many times found they were creating scenarios that would lead me to pulling my hair in the office when something went wonky.
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Re: Survey Control Methods

Post by fobos8 »

I think it pays to get obsessed with every little detail when carrying out surveys in particular in getting your control spot on. Its not just about chosing between prisms or checkerboards.

I just spent an hour in the garage calibrating the optical plummets on two of my Leica prims carriers. I can spot if the bubble levels are out in the field and fix them quickly, the plummets need a bit more attention if they're out.

If you not centred over your nail in the first place, your control stands little chance of being usable.
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Re: Survey Control Methods

Post by jcoco3 »

Speaking of calibrating optical plummets...

Anyone know how far they have advanced in total stations today? My experience with optical and laser plummets is that they are designed for the working distance of a tripod and not too much farther. In the case of a control network for a tall building it has always boiled down to finding ways to obtain direct line of sight shots from a external control network from ground level and adjacent buildings to many levels and the roof. Then on the inside the use of a plumb bob either through holes drilled in the floor or down elevator shafts, etc. We have even built special contraptions and plummet targets in an attempt to make this easier. Basically, I was told that the optical plummet does not have the accuracy necessary to maintain a plumb line very far. Perhaps it is decent from floor to floor, but any amount of error can stack up quickly. Much like flipping the scope and taking numerous shots, I have found that I can rotate the total station with a laser plummet which draws a circle on the floor around the center of rotation. It is only perceivable when the laser plummet is used over very long vertical distances. Probably a terrible way to use a total station, which is why I mentioned it in hopes that you guys can educate me.

I would really like to hear anyone's opinion or experience with this, as it still seems like there is room for improvement here. At a minimum I need to learn more about the accepted methods, and I hoping somebody has another white paper to share on this. I wonder if somebody made a total station that had a hole in base and could fire the EDM through it as the plummet if that would be better? No doubt this has been thought of by the engineers and discarded for numerous reasons.

Wow, this thread is becoming more of a general total station thread rather than implementing survey control specific to Faro scanners. I take the blame for sidetracking...Oh well, its all good info :D
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Re: Survey Control Methods

Post by Least »

You need something like this for accurate plumbing between floors amongst other uses

https://www.pinterest.co.uk/pin/730286895801078024/

You can also get laser versions these days.

And perhaps get yourself a copy of 'surveying for construction'

https://www.google.com/aclk?sa=L&ai=DCh ... t=1&adurl=
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Re: Survey Control Methods

Post by jcoco3 »

That's perfect! I more than likley will not be the person performing that type of survey, but I am sure glad to know what to look for or suggest next time. Thanks.
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