Worse coordinates?

[+89SC]

What are the worse posted coordinates that you have found? I was looking for JX1756 which is listed as being on the east bound bridge over Arnold Creek on Rt 50. The posted coordinates where around .6 mile off. The map shows the benchmark as being way north of Rt 50. The purple road on the map is Rt 50. The red cross shows the posted coordinates and the red box is the bridge.

 

 

The worse I came across before that was only 300'.

[+GrizzFlyer]

The worst I've recovered are for LA0495 and LA0496. Both off by over 50 miles.

 

The worst for a benchmark with adjusted coordinates I've recovered is for MC1262 . Off by 1.25 miles.

[+YeOleImposter]

The worst I've recovered are for LA0495 and LA0496. Both off by over 50 miles.

 

The worst for a benchmark with adjusted coordinates I've recovered is for MC1262 . Off by 1.25 miles.

 

I wanted to doubt your MC1262 because of the '1961'visible on the disk but plugged the coordinates into the map and sure enough, someone made an error on the datasheet.

[DaveD]

LA0495 and LA0496 were obviously confused with marks of the same designation (1 and 2) LA0165 and LA0166. I will check their positions and issue a change request to the NGS database team. MC1262 will be interesting to investigate. The only explanation I can think of at this time without reviewing the observational data is that the station is what is referenced as no-check, meaning that there are only the minimal observations required to solve the position and no enough to check or validate those values. Since all of the observations were keyed in by hand back in the late 70s it's possible that one of the observations was mistyped. I'll see what I can find when I get back to the office later this week.

 

Thanks for bringing this to our attention. It is important that we try and make the data in the National Spatial Reference System as close to perfect as is possible.

[DaveD]

I have submitted correction requests for LA0495, LA0496 and JX1756 to update their scaled coordinates. I've also challenged one of our younger employees to find out what's wrong with MC1262. Since that one is has adjusted horizontal coordinates it will probably require that the original field records be retrieved from the archives and reviewed for any typos in our database and could take some time. Also since it's only a third-order station and has not been updated with more contemporary GPS observations it won't be very high on the "honey-do" list. I will try to keep you posted on this.

[DaveD]

The scaled coordinates for JX1756, LA0495 and LA0496 have been corrected. Thanks to 89SC and Grizflyer for bringing these large discrepancies to our attention.

[+wvhillbilly59]

There are some along the old Route 66 between Chicago and St. Louis which are .1 to .25 miles off of the descriptions.

[DaveD]

Scaled positions are accepted by NGS as being approximately 6 arc seconds in error - this equates to approximately 630 ft (0.12 mi.). If you find something significantly different than that let me know and I'll research it.

[+Harry Dolphin]

Okay, Dave. Take a look at this one. LY2248. Looks like a typo.

Listed coordinates: N 41 09 42 W 074 23 10.

Handheld GPS coordinates: N 41 09 41.4 W 074 23 39.2

It looks like they meant to list: N 41 09 42 W 074 23 40, but typed a 1 instead of a 4 on the west seconds.

[2oldfarts (the rockhounders)]

According to Google maps this one L 403 is about .9 miles off.

 

Given coordinates are N 36° 42.450 W 111° 34.733.

Actual coordinates are N 36° 42.701 W 111° 35.666.

 

John

[andylphoto]

Interesting thread. I haven't really kept track of discrepancies in scaled coordinates, but None that I've seen have been off by quite that far. The worst one that I can recall was a set of two markers with adjacent PIDs and designations, one in the first pier north of the south abutment and one in the first pier south of the north abutment of the same bridge. The were also sequentially numbered "backwards." i.e. the first PID numerically was the second designation.

 

As if that weren't confusing enough, coordinates place BOTH markers at the north end of the bridge. At least two GC logs prior to mine confused which was on the north and which was the south end, either specifically stating such, or by referencing nearby development in the wrong log.

 

See AB7635 (X 346)

and AB7636 (W 346)

 

The stations are correctly placed in reference to their position on the east/west side of the bridge, but the coordinates for AB7636 are off by about .25 miles as it's position is actually on the SOUTH end of the bridge.

 

Given coordinates: 47 07 29 (N) 88 34 25 (W)

Actual coordinates: 47 07 20.3 (N) 88 34 25.3 (W)

Edited January 8, 2008 by andylphoto

[+seventhings]

I have found several (maybe four or five) marks where the discrepancy between the published SCALED coordinates and my handheld was in the 0.3 - 0.5 miles range. Typically, though, the difference is more like 100 feet plus or minus 50 feet.

 

I often wondered how the coordinates could (occasionally) be so far off, but one search that I did offered some strong circumstantial evidence as explanation.

 

I went in search of two marks: KV4832, (the spire of) St. James RC Church, in Woodbridge, NJ, and KV0202, PBM B48 33AMS, a chiseled cross on one of the church's porches. The church was described as located in the southwest angle of the intersection of Amboy Ave and Grove STREET. When I got there I saw that the described location was occupied by a 1960's vintage school, and I concluded that the old church had been razed (there was a new church across the street in the northwest angle of the intersection). I also concluded that the chiseled cross had been destroyed along with the rest of the church. But I noted that my GOTO indicated that the chiseled cross' coordinates were located about 0.5 miles to the north. Curious, I drove north on Amboy Ave and followed my GOTO to the intersection of Amboy Ave and Grove AVENUE.

 

This is what happens, apparently, when you scale coordinates off an old ESSO street map.

 

w

[Bill93]

I have found instances where a mark was set and described in the 1930's, the named road was moved a mile or more afterward, and the scaled coordinates must have been taken off the map after that because they were along the more recent road and not the route that was there when the mark was set.