Over the weekend I downloaded a PA orthophoto and the LIDAR overlay that in fact crosses the Delaware River and includes the Jersy site I discussed last week. The LIDAR shows a 6-8' difference. Previously this other surveyor though I was just being skeptical of a poorly written data sheet description. The LIDAR convinced him to do a check if only to prove me wrong.
Today we did a level run loop from another NGS benchmark ("J 11"/KV1428) to "L 362 Reset"/KV2878 and found a 7' discrepancy. Then we confirmed our loop from "L 362 Reset" to the project. Tomorrow we GPS a project control point to confirm today's work and calls will be made. The old ties on the datasheet show the mark was in an area on the footbridge approach now under newer handicap accessible ramps. The other surveyor was sure this mark is in the same spot when he used it many years ago. Ah, and I am sure all the girls I ever dated were tens or better. There is no third benchmark anywhere near close enough.
GPSing "L 362 Reset" is doable with some method of clamping a 12' rod to concrete walls and/or steel bridge structure, which might get the Homeland Security camera watchers in an uproar. That would be an entirely separate project.
Paul in PA
Level Run Confirms disk isn't the one onNGS Datasheet
Glad you figured out the situation before any harm was done (other than effort expended).
There is nothing wrong with the data sheet discussed in the [msg=135422]other thread[/msg]. It describes a bench mark disk "L 362", KV2878 that may or may not still exist (could it be covered over?). The fact that PA DOT recorded a notation that they did a reset indicates that they expected the older disk to be destroyed or become inaccessible - that is all it means.
A disk stamped L 362 RESET is a different bench mark, for which no data sheet appears to exist (unless PA DOT has one internally). NGS wouldn't modify the data sheet of KV2878 with the elevation of a reset.
Level Run Confirms disk isn't the one onNGS Datasheet
I regret that situations like this are far too common. On numerous occasions NGS would supply a disk for a "Rest" bench mark typically to a state DoT only to see the mark set and then never have the leveling data submitted back to NGS for processing. This is one of those cases, the mark that Paul found is not KV2878.
Around here- there was a time period- 1955-1960ish that the MDOH would reset the same cap in a new location, but stamped "reset" no descriptions exist in NGS but sometimes you can find them on the AS-Builts with the new description sta and offset and a new elevation- You might look there.
I have come across more than once instance where someone actually moved a geodetic monument and reset it in another location. The most recent was in a fence line where the property owner cleared the brush with a Cat and then reset the concrete monument after the new fence was built.
[sarcasm]I will bet that cat was really po'd after going through all that brush and knocking out that monument!! [/sarcasm]
Sorry, I just couldn't resist an variation on some old jokes.:-X
I have seen LIDAR actually be off that far. We checked and double checked our work using GPS both VRS and OPUS. We had the LIDAR information and compared it to our field run topo and found similar discrepancies, but it wasn't consistently off that much, it was spotty. It is very unsettling to say the least.
Level Run Confirms disk isn't the one onNGS Datasheet
Howdy,
I agree completely with Bill. Users who refuse to read and understand the contents of an NGS data sheet should not use them. If I adamantly insist on using the wrong monument then complain about failing to get good values, who is the "bum".
I recollect a conversation with a surveyor who asked me why he couldn't use the dynamic height on a data sheet rather than the published NAVD value because it checked better. I am glad I retired.
As far as folks taking it on themselves to "replant" a disturbed monument, I had a landowner berate me for removing the disk from a benchmark monument that as completely out of the ground. He had fond feelings for the monument and "...would have stuck it back in the ground if he knew I wasn't going to..."
Read the data sheets. If the stamping does not agree with the description, if it is a rod and not a disk, if the agency shown on the disk is not the same, DON'T USE IT AS IF IS THE MONUMENT described in the NGS data sheet.
Sheesh...
DMM
Level Run Confirms disk isn't the one onNGS Datasheet
> Howdy,
>
> I agree completely with Bill. Users who refuse to read and understand the contents of an NGS data sheet should not use them. If I adamantly insist on using the wrong monument then complain about failing to get good values, who is the "bum".
>
> I recollect a conversation with a surveyor who asked me why he couldn't use the dynamic height on a data sheet rather than the published NAVD value because it checked better. I am glad I retired.
>
> As far as folks taking it on themselves to "replant" a disturbed monument, I had a landowner berate me for removing the disk from a benchmark monument that as completely out of the ground. He had fond feelings for the monument and "...would have stuck it back in the ground if he knew I wasn't going to..."
>
> Read the data sheets. If the stamping does not agree with the description, if it is a rod and not a disk, if the agency shown on the disk is not the same, DON'T USE IT AS IF IS THE MONUMENT described in the NGS data sheet.
>
> Sheesh...
>
> DMM
:good: