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Two Designations Sharing Same Disc?

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Was up north this weekend at the cabin, had my data sheets and did some benchmark hunting, and I didn't realize it until I returned home that I had found something I hadn't run across before.

 

It would seem that SKELTON RM 2

 

http://www.geocaching.com/mark/details.aspx?PID=RN1668

 

and 0980 L

 

http://www.geocaching.com/mark/details.aspx?PID=RN0812

 

share the same disc, but both have different PID's and data sheets. Is this normal? Why would they re-stamp the disc with a different name? Is this because they wanted to make an existing disc a reference mark for a station thus giving it dual names so the one name would correspond with the station it references?

 

Thanks!

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I have not seen this before, but I don't see a problem with it. As SKELTON RM 2 it has an adjusted horizontal location but poor vertical data (VERTCON).

 

They came around later and measured the elevation accurately for 0980 L. This is in a series, so they probably wanted to use the next designation in their series even if it was a pre-existing disk.

 

Maybe because the vertical data was submitted with a new designation, it would up as two different data sheets, one for each kind of data.

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Was up north this weekend at the cabin, had my data sheets and did some benchmark hunting, and I didn't realize it until I returned home that I had found something I hadn't run across before.

 

It would seem that SKELTON RM 2

 

http://www.geocaching.com/mark/details.aspx?PID=RN1668

 

and 0980 L

 

http://www.geocaching.com/mark/details.aspx?PID=RN0812

 

share the same disc, but both have different PID's and data sheets. Is this normal? Why would they re-stamp the disc with a different name? Is this because they wanted to make an existing disc a reference mark for a station thus giving it dual names so the one name would correspond with the station it references?

 

Thanks!

I've found the same thing in Brooklyn.

 

KU3532 "PROSPECT WATER TOWER 1903", a triangualtion station with adjusted coordinates, is a copper bolt in a granite post which marks the spot of the former water tower which was torn down in the 1930s. The original station dates from 1903.

 

KU1297 "22" is a bench mark established in 1952 with scaled coordinates using the same monument (the copper bolt).

 

They have separate data sheets and for all you would know from reading the logs, the surveyors who established the bench mark "22" in 1952, were not even aware of what the monument was.

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Since they each have different coordinates they can't be on the same disk. Skelton is at N46 30.318 W092 40.467 and 0980 is at N46 30.267 W092 40.483 .1 miles different. I have no idea what the problem was when they set them but I don't think that they are at the same location. I'd check the other coords and see what's there.

 

Dave

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Since they each have different coordinates they can't be on the same disk. Skelton is at N46 30.318 W092 40.467 and 0980 is at N46 30.267 W092 40.483 .1 miles different.

 

Except for the fact that the coordinates for 0980 L are scaled, which by definition means they may not be exact. The altitude for 0980 L is adjusted, which means that this altitude should be trusted, rather than the altitude for SKELTON RM 2, which is scaled.

 

The descriptions also describe the same corner of the same bridge on the same road, including the same bridge number. That would lead me to believe that the scaled coordinates are .1 mile off. I'll agree with the same disk being used for two distinct PIDs. I haven't seen that one before...good thread.

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Since they each have different coordinates they can't be on the same disk. Skelton is at N46 30.318 W092 40.467 and 0980 is at N46 30.267 W092 40.483 .1 miles different. I have no idea what the problem was when they set them but I don't think that they are at the same location. I'd check the other coords and see what's there.

 

Dave

Hi Dave

 

The problem is with the location of the benchmark (0980), which is scaled. The same situation exists with the two stations in Brooklyn I mentioned. Namely, the leveling crew came in after the disk (or copper bolt in Brooklyn) was already there for the Triangulation Station. They did their work and left the description (Southeast corner of blah blah).

 

Then when the records were computerized, the clerks who did the work estimated the location from a topo map (as is true for all scaled locations). They did not know or did not bother to check that the location was already accurately known from the other station's data sheet. So now the disk has a accurate location as a tri-station on one data sheet, and a bad location as a bench mark on the other data sheet. But yes it's the same disk.

 

A similar thing can and often does happen when reference marks are used for bench marks, usually long after they are set as reference marks. Station KU3890 "PALISADES" in NJ has 2 reference marks set in the 1930s. In the 1950s, they were both used as bench marks and so they received separate PIDs and new data sheets (see KU1644 and KU1645). However they did not bother checking the original locations (given in the box score for KU3890) so the disks got new scaled locations on their separate data sheets. It turns out that the scaled locations of the reference marks as a bench marks are on the other side of the I-95 from the same disks as a reference marks. Click on the links above and just glance at the little maps and you'll see.

 

It happens more than you think.

 

Bottom line: Ignore the scaled coordinates on the bench mark version of the disk.

Edited by Papa-Bear-NYC

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I have forwarded a correction request to the NGS data base team to take the position listed for RM 2 and add it to the height for 0980. This happens from time-to-time. The PID for RM 2 will be deleted from the database.

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Thanks for all the interesting feedback and discussion. I guess being fairly new to the whole benchmark hunting process it would be only a matter of time before I ran into something that was out of the norm for me. I feel a little better knowing it "happens more than I know" and what Papa-Bear said there does make sense.

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