I'm hearing lots about 0.1' and 0.2' errors and was not surprised.
Lets say there is a 1" Iron pipe up 36". The pipe is reasonably plumb, but maybe 5 degrees out. DO you locate the top of the pipe or the bottom?
DO you put the rod on the side of the pipe and have the I-man turn to the center?
DO you put the rod behind the pin and cheat the prism toward the instrument to compensate?
Seems like these differences could easily amount to your 0.1 - 0.2'
> I'm hearing lots about 0.1' and 0.2' errors and was not surprised.
>
> Lets say there is a 1" Iron pipe up 36". The pipe is reasonably plumb, but maybe 5 degrees out. DO you locate the top of the pipe or the bottom?
>
> DO you put the rod on the side of the pipe and have the I-man turn to the center?
>
> DO you put the rod behind the pin and cheat the prism toward the instrument to compensate?
>
> Seems like these differences could easily amount to your 0.1 - 0.2'
That's a standard of care issue, do you locate evidence as if you were taking a topo shot?
We used to double up on any thing ever found that could be used as retracement evidence. Most modern data collectors have all those options built in, so you could measure using a variety of suitable options.
Ralph
Generally where I see pipes sticking up that far is rural timberland. So for purposes of reporting measurements to the pipe I use the top center and don't worry about the lean if it is minor. If it is leaning significantly, like 45 degrees, then I consider going for the Gazinta or if we rehab it then we shoot it after rehabbing. But in rural timberland we aren't splitting hairs.
It depends on where you are.
In the forest where a 3' tree is small then a few tenths is nothing.
I turn 4 sets to found monuments, usually from the backsight then another 4 from the next traverse station ahead. It can be a problem to locate a monument from two control points, particularly in rough brushy terrain with a lot of large trees.
I use 12" spikes for control points for stability.
I agree that it is a judgement call, but given today's technology it really a budget buster to take a little extra care when locating evidence.
Ralph
That's exactly right. It isn't that hard to do. The data collector records all of those angles and distances for me. Least Squares software processes it and lets me know what the residuals are so I can fix blunders in the data.
If you know what you are doing, you stick the prism pole in the top of the pipe, and torque the prism pole plumb, and presto, you have got it right, no matter how many time you wind up the cotton pickin angle!
Just kidding!
Snork!
N
Any time a monument is leaning like that I use the offset function in the data collector to locate the center of it at ground level. I'm usually using a robotic gun so I have complete control of the shot, but if there is an instrument man I'll have him do the same thing.
In some cases it may not be that critical, but it's no trouble and it helps me sleep better, so why not?
Chris B.
I usually find it easier to set a tripod/tribrach and target over it rather than a prism pole.
It's a matter of judgement. I try to shoot as close to the ground position as possible. If it's leaning, I'll turn to the center of the pipe at the lowest point. If using Gps, we try to get as close as we can. I typically assess why a pipe is up that far. Did they hit a root, rock, etc., and not try to set the pipe flush. Was there an erosion issue (in which case the pipe may have moved with the dirt). Was it moved by a third party. Basically it opens the door to dozens of questions. In my opinion our job is to measure as close as possible, to the intended position. There are several right and wrong ways to measure it.
I might also add, that in Kansas we often try to drive the pipe down to ground level. Often we find pipes in Section Corner locations on dirt roads. If at the surface and in danger of being hit by a grader. We will lower the pipe a few tenths under the surface, to preserve the position.
Forest monuments usually stick up at least a foot and a half just so there is some hope the Loggers will see and avoid them.
It is also fairly standard to blaze bearing trees and set yellow metal Bearing Tree tags.
I worked back west for 15 years. I remember blazing tress, and yellow tags. I used to cut bark of healed trees, to see the reverse blaze in the bark. Here there aren't many trees.
I locate the top, locate the approximate location where it would intersect the ground.
If the pipe is bent, would the bend be at the ground level? Unless you see the bend, it's probably a bit further below the surface. I'd hold the pipe for line in the direction it appears to be bent and see how the record math works.
Dave
> I usually find it easier to set a tripod/tribrach and target over it rather than a prism pole.
you actually set up a tripod over every iron pin you locate? We did a 3 hour job the other day and probably located 20 Pipes, monuments and rebars.
Sounds like I found the 0.2 already
SOme guys locate the top of the top, some guys locate the bottom of the pipe. 3' is a little excessive, but very few pins are flush around here, even on residential lots. They usually stick up a foot or so.
Dave
not necessarily but sometimes there is only a monument every 1/2 mile and it is a rough hike back to the truck just to retrieve the prism pole.
We don't force center but I do set up the instrument on tripod already set over the next traverse point ahead.
On smaller projects with a lot of monuments to locate then we do use the prism pole more for that.
Dave
When I run the rod thru the woods, I carry a tripod w/prism setup and mini prism and plumb bob.
Sounds like I found the 0.2 already
> SOme guys locate the top of the top, some guys locate the bottom of the pipe. 3' is a little excessive, but very few pins are flush around here, even on residential lots. They usually stick up a foot or so.
Now that you have found the 0.20', help me find the 2.00'. Maybe the stake was 3.00' long and battered over 2.00' and he shot the top:-)
Ralph
Ralph
Sounds like you just have to decide whether the 2 foot off pin placement is original or whether it has legs. Does the 2' make a big difference as far as lot development goes? Like does it put any houses or drives over the setbacks?