I'll try this without a picture.
I set up on a point (A), and backsight to a known point (B), due East, 150.00' away.
Turn right exactly 90 degrees (South), and shoot another point(C) that is supposed to be on that line. Except it's not.
It's actually on a line that is S45'15"E. This is huge.
So, either:
a) I measured the angle incorrectly, or
b) I measured the angle correctly, and angle B-A-C is NOT a right angle.
C is not visible from B, so my thought is to go about 150' up the line A-C, (set a target (Point D) that is, and use trilateration, relying on EDM between B-A, B-D and A-D to confirm the angle one way or another. If the instrument is capable of +/- 3mm + 5ppm, it seems it would certainly be able to confirm such an error if it exists, given that 45' would amount to almost 1.9 feet, 150feet up the line.
Ghilani and Wolf don't spend much time on Trilateration (except in the context of geodetic surveying) , but Davis Foote and Kelly do.
Would this single triangle achieve the task, so long as instrument errors are known?
Is there an easier way?
Shoot them all with RTK!
What tells you it should be a right angle?
Does it look more like a right angle or a 45 degree angle?
S0°45'15"E, I think??
> Is there an easier way?
With a picture.
Duh. I should read more carefully.
Still, why do you think it is a perfect 90?
Just do it again.
If you cannot rely upon your instrument to turn one angle you have bigger problems than this one.
> Just do it again.
>
> If you cannot rely upon your instrument to turn one angle you have bigger problems than this one.
:good:
> Still, why do you think it is a perfect 90?
I will draw and scan a picture, but the simple answer to that question is: the plat I'm looking at says it should be. A friend of mine (a retired LPS)took a look and answered the question by saying "because he did it in the office"!
The comment below about knowing and trusting your instrument is a good one. I took these measurements prior to the unit being professionally calibrated (and my ongoing "Kent Test I and Kent Test II"), so I'm considering redundant measurements (that rely on edm instead). When the instrument returns, obviously the first thing I'll do is re-measure the angles, but I just don't think it's a blunder.
> Shoot them all with RTK!
Way too many trees!:-D
Why would it be a 45° unless both lines AB and AC are exactly 150' (or exactly the same distances as each other). Maybe I'm not understanding your setup. Turn all three angles if you can. If one is exactly 90, the other two will add up to 90 (ie: all three angles will add up to 180)
> Why would it be a 45°
I think my initial notation ( S45'15"E) misled some. It's NOT S45°15'00"E...It was supposed to be S0°45'15"E. I left out the degrees.
That said, here's the picture:
The calculated angle is 89°38'36", not 89°45'15" as previously stated, but the situation remains the same. Angle B-A-E should be 90 degrees, and if it were, A-C-E would be a straight line. It doesn't appear to be.
The proposed Tie Line to Point D using EDM should confirm the angle.
RFC-
Dig out your 3/4/5 rubber boots per second measuring machinery and 'ave a go.
You may use a tape too 😉
Reference may be had to:
http://en.wikipedia.org/wiki/Pythagorean_theorem
Remaining,
YOS
DGG
How old is the survey you are working off of? Here in pa, it's not terribly uncommon to find surveys that are only accurate to within a half of a degree, sometimes only to the nearest degree. If it's from that time period, that's not a drastic difference of angles. Meaning the error would have been in the precision of the original survey. I would hold any found monuments, and then hold the deed bearings and distances from the found monuments, after looking for more evidence to support it.
> RFC-
>
> Dig out your 3/4/5 rubber boots per second measuring machinery and 'ave a go.
>
> You may use a tape too 😉
Aye, Mate! A fine idea she be!
Except that the difference in elevation between B and D is almost 30', and my ancient Lufkin 200 footer steel tape snapped a couple weeks ago at the 20' mark (No, I DIDN'T kink it! I'm a rookie, but not that much a rookie);-)
Even if it wasn't broken, in my early trials with plumb bobs on both ends, I kept pulling my wife over tensioning the tape.:-D
Bottom line: I don't think I could come anywhere close with a tape.
2013. Survey was done with a 3" instrument, however, there is a note that says:
"Bearings shown on this plat refer to Grid North as established by OPUS Observations using Topcon Hyperlite + GPS Receivers".
Maybe that's the problem...That RTK stuff...Can't trust it as far as you can throw it! 😀 It IS, in fact, under a dense canopy of trees.
RFC-
Ahha! The dreaded chain break.
How about using stadia ?
Should not be too arduous for a young laddie and his lassie, nipping up and down 30 feet.
Cheers,
Derek
PS-
Sorry about the YouTube in metric.
Ludditely speaking ...............
The OZ squad likes to hamstring itself using a unit that is statistically not repeatable using cadastral measurement techniques to three places of decimal !
It sounds like you have more than one bearing basis.
:{:
I remember back in my formative years with only a stinking 10 second K & E, we would just "buck in" or "wiggle in" or whatever anybody calls it in their zip code. You set the gun in the middle somewhere, and sight one, flop and see where it hits the other one. Keep doing it until you are gizmoed to satisfaction. Then double triple three rail your shots until the goats get full. I didn't even have an EDM and they hadn't even invented data collectors yet.
Don't blame it on the trees or a hill either. Those are work around's. They were here first and sometimes are.... no I won't say smarter, but have more longevity and will likely out live all of us.
In the old days, in the infancy of calculators and my surveying experience, just about all miscalculations could be tracked down to forgetting to convert an angle to DMS, converting it twice, or going the wrong way.
What are your field angles turned in the field?