Benchmarking - What is a reset disk?

[+Revent]

New to benchmarking, but found a very interesting document on the NGS website about exact what a reset disk is, and how they are established.

 

http://www.ngs.noaa.gov/PUBS_LIB/Benchmark_4_1_2011.pdf

 

Apparently if a disk is reset it is ONLY because the original disk was destroyed, and if it's not listed as destroyed that is an error. The new disk location (elevation, usually) has to be referenced by geodetic methods to the old mark before it is destroyed...it's not just a replacement, it's a mean of preserving the original geodetic information.

 

For us, I guess that would mean if a station has a longstanding reset, and cannot be located, we should point out to NGS that they forgot to set the old station to 'destroyed'.

Edited January 12, 2014 by revent

[+Revent]

New to benchmarking, but found a very interesting document on the NGS website about exact what a reset disk is, and how they are established.

 

http://www.ngs.noaa.gov/PUBS_LIB/Benchmark_4_1_2011.pdf

 

Apparently if a disk is reset it is ONLY because the original disk was destroyed, and if it's not listed as destroyed that is an error. The new disk location (elevation, usually) has to be referenced by geodetic methods to the old mark before it is destroyed...it's not just a replacement, it's a mean of preserving the original geodetic information.

 

For us, I guess that would mean if a station has a longstanding reset, and cannot be located, we should point out to NGS that they forgot to set the old station to 'destroyed'.

 

Reading further, "Attachment B", about how a new station is established, is very interesting also, though the instructions about how to mix concrete are a bit tendentious.

 

"Attachment C", thought, is about how to write a station description...I've seen a lot that were "Mark found' or something similar for 50 years, without noting that the road referenced have been paved and named, fences torn down, etc.

Edited January 12, 2014 by revent

[+dprovan]

Apparently if a disk is reset it is ONLY because the original disk was destroyed, and if it's not listed as destroyed that is an error.

I'm no expert, and I have to admit I only skimmed the document, but it seems clear that setting the reset disk is independent of the destruction of the main disk, except in that the destruction is being anticipated. In particular, it clearly talks about destroyed or disturbed bench marks. That agrees with other things I've heard, including cases where a reset disk was set, but then the original wasn't destroyed, after all.

 

For us, I guess that would mean if a station has a longstanding reset, and cannot be located, we should point out to NGS that they forgot to set the old station to 'destroyed'.

I think this part is clearly not true. The document says the NGS requires proof of destruction. If they don't get the proof, the old station won't be declared destroyed no matter how many reset marks have been set. And this doesn't surprise me, either, since this document doesn't preclude the case of an old station being made unavailable without being destroyed, paved over, for example.

[+Revent]

Apparently if a disk is reset it is ONLY because the original disk was destroyed, and if it's not listed as destroyed that is an error.

I'm no expert, and I have to admit I only skimmed the document, but it seems clear that setting the reset disk is independent of the destruction of the main disk, except in that the destruction is being anticipated. In particular, it clearly talks about destroyed or disturbed bench marks. That agrees with other things I've heard, including cases where a reset disk was set, but then the original wasn't destroyed, after all.

 

For us, I guess that would mean if a station has a longstanding reset, and cannot be located, we should point out to NGS that they forgot to set the old station to 'destroyed'.

I think this part is clearly not true. The document says the NGS requires proof of destruction. If they don't get the proof, the old station won't be declared destroyed no matter how many reset marks have been set. And this doesn't surprise me, either, since this document doesn't preclude the case of an old station being made unavailable without being destroyed, paved over, for example.

 

Heh, pardon my 'imprecise language'... by destroyed, I did not mean the step of setting the 'condition' as X (destroyed, which requires positive evidence, a disk), I meant a 'recovery note' mention that the mark 'no longer exists'.

 

There are quite a few stations in my area that were originally set on Tx Highway Department structures (bridges, culverts) that were reset by the highway department before the original station was obviously 'destroyed' (it's pretty clear when a several hundred foot bridge no longer exists, heh) though obviously not formally by NGS standards.....the issue would be that the original station has then been reported as 'mark not found' for twenty+ years, and there is nothing in it's datasheet that indicates that the existing bridge is not the one it refers to.

 

TXHD 'apparently' had a policy at one point of transferring the benchmark to temporary markers, destroying the original structure, and then reusing the original NGS disk (with a RESET stamp) at the new location....this would not be classified as NGS as a "formally destroyed, condition X" station, but the datasheet for the original should have a recovery note indication that the original structure is no longer in existence, at least IMO.

[+Revent]

Again, imprecise language.....there are NGS datasheets that indicate in the 'recovery notes' that the station has been destroyed, without the station itself being set to condition 'X'.

[+Ernmark]

You'll also run into many stations where both the reset and original mark still exist and are in the NGS database..