I see a lot of discussion on the precision of instruments, which is interesting, but totally over the top if you do not know your personal precision.
So what is your personal pointing precision?
Mine was 1" when I was much younger and I seriously doubt it has gotten and better.
I took the test using an 0.3" optical theodolite with 32 D&R observations on a distant target. My meaned observation error was 1 second. That personal error gets added to both ends of any angle observation, along with setup, centering and all those other errors.
Paul in PA
First, let me change the subject line
(...)
Just kidding, Paul.
Moving on...
Excellent point and one I had thought of as well on these other discussions on machine precision. How good are the focused crosshairs relative to your eyeball?
What's in YOUR Precision?
> I see a lot of discussion on the precision of instruments, which is interesting, but totally over the top if you do not know your personal precision.
>
> So what is your personal pointing precision?
Assuming that what you mean is "What is the standard error of pointing the telescope of a good quality total station or theodolite at a well-defined target in sharp contrast?", the answer is that it depends mainly upon the magnification of the telescope. If you were unable to point a first-order theodolite at a target with a standard error of point well under +/-1", then the problem was probably as much with the target as with the observer.
The usual empirically derived values for the standard error of point are:
Distant targets in poor contrast: 20"/M, where M = Telescope magnification
Close range targets in good contrast : 12"/M
So, for a 30X telescope the pointing uncertainty would be expected to fall in the range between +/-0.40" and +/-0.65". Naturally, much worse results can be obtained under adverse conditions.
I've always felt that part of working with the client and getting things right at the same time, meant you kind of worked to the requirements of the job. Splitting gnats butts on a 6 legged open traverse though thick woods is a joke. Find something there thats close when you reach your destination. Then you do cartwheels.
Then there are times to check, double check. Ok fine. I'd rather traverse through the woods.
0.3" gun. huh. Those are in factories bolted to the floor working in sub millimeter tolerances. There are no eyeballs involved. Certainly not one in any survey truck I've ever seen. Heck, even NGS isn't that good...;-)
I don't quite fully understand the question or the problem. Whatever the point is your finding or setting, just get it in the right spot. End of story. We have BTR's to tell us what to do.
> I don't quite fully understand the question or the problem.
I think Paul's point was that he's merely pointing (no pun intended) out the limiting uncertainty in any optical angular measurement involving a human observer will be the uncertainty with which that observer can actually point the total station or theodolite telescope at a sharp, well defined survey target. His claim that he can't point such a telescope any closer than +/-1" should not be the case for most experienced observers with unimpaired vision.
> I don't quite fully understand the question or the problem. Whatever the point is your finding or setting, just get it in the right spot. End of story. We have BTR's to tell us what to do.
I'm with Kent on this one. It's not about splitting gnats butts. It's about knowing where the errors traditionally seen in surveying come from, be it the operator or the instrument, or something else.
In my personal case, (unlike seasoned guys like you, and many here), I know squat. So I want to know WHY, if I get to the end of the "six legged traverse through the woods", if the "iron pipe and stone post" I'm looking for is .2' away from where I thought it should be, why that is...is it the instrument? Or something I'm doing?
I'm guessing that Paul's idea is: As technology gets better and better, the conventional thinking might be that need for personal excellence is diminished, but that we still need to know what that personal factor is.
Guys like you learned long ago, what your instruments are capable of and what you are capable of. I think you develop a sense (measured or not) over time of these factors.
From what I've learned so far, I think that if I were hiring a surveyor today, I'd opt for someone with an optical theodolite who'd been doing it 20 years, over one in the biz for two years, with the latest RTK satellite stuff.
Bottom line: Your comment about "getting in the right spot" is great; it's just that the "right spot" is not an absolute place...there will always be tolerances involved.
I guess that it has something to do with all the baloney you have eaten.
Not saying that you are full of baloney or anything like that y'know.
WW2 pilots in Europe would drink bilberry juice believing that it improved their eye sight.
The usual empirically derived values for the standard error
Kent cites accepted formula, all well and good.
The questions is has Kent ever checked his personal capabilities against accepted standards?
As to the 0.3" theodolite, it is a field instrument, set on pedestals to check dam deformation. For the pointing test it was set on a standard tripod. Besides testing visual acuity a personal pointing test measures the dexterity in your finger tips in handling the horizontal circle knob. Turning an instrument in 1" increments is not that easy.
Unless you have access to such a precise instrument to do your test you cannot claim any precision greater than your instrument's least count.
It appears that I may not meet Kent's and other's standards, but I have no complaint. Personal 20/350 (right eye) uncorrected vision with moderate astigmatism and I have no imagination that I am better than my equipment.
BTW, my left eye is 20/250 uncorrected and I have never done a left eye pointing test. The best comparison is that I shoot tighter 10 shot targets (iron peep sights) with the left eye than the right, but all my equipment (surveying and rifles) is set up for a right eye, right hand world.
Paul in PA
As technology gets better and better...
...too many people think it can obviate their own shortcomings.
Paul in PA
The usual empirically derived values for the standard error
> The questions is has Kent ever checked his personal capabilities against accepted standards?
Well, yes, in the sense that you can back the pointing error out of the standard error of a direction taken as the mean of Face Left and Face Right. The Zeiss one-second theodolite that I have tests at +/-0.88" s.e., so obviously the pointing error is much smaller than that.
> As to the 0.3" theodolite, it is a field instrument, set on pedestals to check dam deformation. For the pointing test it was set on a standard tripod. Besides testing visual acuity a personal pointing test measures the dexterity in your finger tips in handling the horizontal circle knob. Turning an instrument in 1" increments is not that easy.
What was that a Bostrum 0.3" Theodolite and Farm Level? The Zeiss one-second theodolites I've used have very fine motion screws. Setting the telescope on a target is not the problem that you describe. I think that the problem most likely was the target wasn't a very good one. Pointing a theodolite telescope at a target such as a star with an angular width less than the reticle can have some personalistic bias, but I wouldn't expect that to be true for a high-contrast survey target that is well defined (excellent seeing, no shimmer or blurring).
I think the real question here is, Can you beat your Robot?
I hear of too many folks that adjust the citing of their robot.
If you really want a conversation, I suggest doing the same tests mentioned robotically. Then compare the results to your eyeball.
I'll donate my time!
> I think the real question here is, Can you beat your Robot?
>
> I hear of too many folks that adjust the citing of their robot.
>
> If you really want a conversation, I suggest doing the same tests mentioned robotically. Then compare the results to your eyeball.
Excellent idea! I volunteer to do the work. PM me to get the shipping address to send the latest state of the art Robotic Total Station to me, to get this done!:-D
Turning an instrument in 1" increments is not that easy.
That was a general comment, not specific to precise instruments.
Using the factory level angle test numbers, implies that you have collimated targets that allow the target to appear at infinity.
However you did not reply to Kent's personal pointing test?
I always thought Kent was much more meticulous than the common surveyor.
Paul in PA
I'll Send You My Robot
It does perfect D&Rs because it turns to the 180° point. But if you look through the instrument you will find the crosshairs centered on other than the target.
It is pretty much an $18,000 boat anchor when considering precision.
Paul in PA
I'll Send You My Robot
It's been mentioned on here many times that a robot's sensor may not be positioned exactly the same as the crosshairs. It may or may not turn good angles, but with each direction reading slightly offset the same amount from the visual axis.
Basic limiting factor is the width of the reticle's "wires."
To overcome that, manufacturers developed the "Impersonal micrometer reticle" that is made of multiple hairs or wires that the observer used to follow a star across the observer's field of view. Needs a printing chronograph to work and an automobile battery. Takes a whole lot of paraphernalia to work together. Now only found in museums.
I'll Send You My Robot
> It does perfect D&Rs because it turns to the 180° point.
My Leica doesn't:
FD,OP11,FP14,AR268.5743,ZE89.5111,SD337.120194,--CONTROL
FR,OP11,FP14,AR88.5730,ZE270.0855,SD337.122491,--CONTROL
That's a typical robotic split from this 10-year-old gun.
Turning an instrument in 1" increments is not that easy.
> However you did not reply to Kent's personal pointing test?
Actually, I did. If I tested a one-second Zeiss Th2 and got a standard error of a direction of 0.88", it means that my standard error of pointing was well below that, closer to the values I quoted earlier based upon magnification.
> Basic limiting factor is the width of the reticle's "wires."
>
> To overcome that, manufacturers developed the "Impersonal micrometer reticle" that is made of multiple hairs or wires that the observer used to follow a star across the observer's field of view. Needs a printing chronograph to work and an automobile battery. Takes a whole lot of paraphernalia to work together. Now only found in museums.
Yes, but that's for star observations, not terrestrial measurements. The width of the reticle really isn't much of a consideration in terrestrial measurements on targets with an angular width greater than the reticle engraving.
