Interesting small project I am doing right now. CSX paid a contractor to replace a bridge carrying a township road over the RR. The old bridge had a USCGS benchmark on it. At that point it would have been relatively simple to replace the mark before it was destroyed. But, it wasn't done.
Now, CSX is requiring the contractor to have the mark replaced. To get it back into the NSRS, this requires running second order levels, using invar rods, etc, and submitting the data to NGS (bluebooking). Also, we have to find two (or more) existing marks that agree within spec.
Interesting that CSX is REQUIRING this.
Most of the marks in the area are concrete monuments (aka concrete post). Most are destroyed. I did find one mark that is set vertical in a school building. I typically assume these are the most stable. We ran from there to a concrete post, then to another concrete post.The latter was a triangulation station which was leveled to. It had two reference marks (also concrete posts) that were also leveled to. One is gone. The result was that the three concrete posts all agree, the vertical mark at the school doesn't.
This would have been much easier BEFORE the mark was destroyed. But, I am impressed that CSX cares about this.
By how much does the vertical mark in the school building not agree?
So what if they replace it, if it is in their ROW they won't let you use it.
Paul in PA
In running second order levels I have proven far more vertical C&GS marks on buildings to be wrong than standard horizontal marks. You tend to remember this stuff as re-running second order circuits is time consuming and expensive.
As for CSX, my guess is that it was in the construction contract, otherwise it wouldn't be an issue.
if you go through their safety course, they will let you use it. at least, that is how it work here.
I always try to go with the "don't ask, don't tell" policy! Camo in rural areas and nice, pretty, shiny vests in populated areas. Works every time. If all else fails, just act stupid...
> I always try to go with the "don't ask, don't tell" policy! Camo in rural areas and nice, pretty, shiny vests in populated areas. Works every time. If all else fails, just act stupid...
:good:
Sometimes, it's easier to ask for forgiveness, than to ask for permission.
John
I'm sure I'm not telling you anything you don't know here. Are all the marks on the same level run or is the building mark on a different run than the other 3? We had a building mark get us once when the face of the building was remodeled and they put it back approx where it had been. It was only off by a few inches. Modern equipment can clearly show a bias between level runs.
At this point why not construct a new mark away from the bridge where its more accessible to everyone without having to contact the RR? Getting permission to survey in RR ROW is really becoming a PITA causing several project scheduling issues.
My heart is more at peace when we work through the proper contacts for survey work on RR ROW. You are one passing train or one rail master visit away from stiff fines or worse if there is ever an accident. Like it or not, the risk is greater than the reward at this point in time.
The new mark is located on the wingwall of an overpass of the RR. So it is in the ROW of the road.
Poor idea
"I always try to go with the "don't ask, don't tell" policy! Camo in rural areas and nice, pretty, shiny vests in populated areas. Works every time. If all else fails, just act stupid..."
Do you understand how poor an idea this is? If you are seen by a railroad employee in the ROW they are REQUIRED to report you, and they will. The fine is a MINIMUM of $17,000... Pretty expensive price for "acting stupid".
This is not in the RR row, it is on an abutment of a bridge over the railroad. Access to the ROW is not required. [sarcasm]If it was, then every vehicle going over that bridge would need a permit, flagman, insurance, etc. [/sarcasm]
It appears that the vertical mark, set in 1959, is in a brick wall that has been at least re-pointed, if not more. It is possible that someone put the mark back in the "same" place when they repaired the wall (i.e. put it back in the same hole). It miscloses about 0.011 m. Once I get everything adjusted I will know for sure, they just finished the job late yesterday.
Interesting picture, it has a hole below the cross. I have seen that on triangulation disks, supposedly to let any trapped air out after it is set. 
That vent hole seems to have been used only for a short time in the late 1950's.
Did somebody mistake the hole for a "datum point" punch mark and shoot it instead of the line? That could explain a lot of the misclosure.
I'm interested in your procedure for getting the elevation off a disk so mounted. I've heard of standing the rod on a knife/machete blade. That at least avoids any problem with the zero point of the rod.
This one is a little low to set up the level at the height of the line. That sounds like a good idea when it is practical, until you realize that if the rod scale zero is not at the precise end of the rod you have an error that doesn't cancel, like it would when the rod is set on horizontally mounted disks.
we used a flat blade screwdriver (sometimes a knife blade), and try to get it horizontal so that the place where the rod sits is the same elevation as the center of the cross. I feel this gives us about ± 1 mm.
We bought a 50 cm invar strip a few years ago to use for exactly this situation (very light and thin), you can hold that right on the mark. Of course the crew forgot to take it with them.
The fact that the cement around the disk is not the same as the mortar between the bricks argues for it being undisturbed. The slight tilt of the "horizontal" line of the disk relative to the bricks is a bit worrisome, though.