Coordinates scaled - Badly off

[+Harry Dolphin]

I do understand the concept of scaled coordinates. Nearest Degree Minute Second from the topographic map. If the scaling is accurate, the station can be 360 (?) feet off. Sometimes transcription errors come into play. This I can understand.

We went looking for four sets of tidal stations. Five stations each seems to be common. Each of the five has the same set of coordinates. No problem. I told myself that we would go searching by description, rather than by coordinates, and GPS. But I did use the coordinates to get in the right area. With three of the four sets, that presented no problem. (Other than the fact that the National Ocean Service had no idea what town they were in. They put three of the sets in Rutherford, when they were actually in East Rutherford, Carlstadt and Moonachie. Oh, well.)

One of the sets was .34 mile off. KV3462, for example is listed at N 40 50 00 W 074 05 03. My handheld GPS gave coordinates of N 40 49 52.9 W 74 04 40.1. That's not even close! And I cannot see any logical reason for the discrepancy. It doesn't look to be a transcription error.

I do reaize that all five have the same coordinates, so it is actually one problem, rather than five. But it seemed like five errors. We searched the original area for a fair while, even though the building numbers were off. Finally, Andy Bear pushed me in the car and exclaimed "Let's go look for the right building numbers." (Dolphin is nothing, if not obstinant.) And, lo and behold, there they were!

Is there any explanation for this sort of error? I see no logical reason. Or was it just some sort of stupid blunder? How common is this?

Note: Coordinates listed are DD MM SS, since that is how they are listed by NGS.

Edited April 10, 2007 by Harry Dolphin

[+NightPilot]

The example numbers could be either dd mm ss or dd mm.mm. Whoever did the original data sheet knows which it is, but I don't. It looks like dd mm ss, but I wouldn't bet the farm on it.

[+Holtie22]

One needs to realize that not all of the information that appears on a datasheet was collected at the same time, or even by the same agency. The provision of scaled coordinates for vertical control points is a relatively recent program of NGS, and was accomplished in the office rather than in the field. Faced with hundreds of thousands of station descriptions for which coordinates needed to be scaled, I think it's commendable that they are as close as they are, which is NOT to an accuracy of the nearest second.

[+PFF]

Finally, Andy Bear pushed me in the car and exclaimed "Let's go look for the right building numbers."

 

Scaled coordinates are bad enough. Thank goodness, Andy Bear got you off of the "scaled building numbers".

 

I'm curious if ANY disk in the cluster matched the coordinates--or was even closer than 3/4 mile?

 

Paul

[68-eldo]

In my area NGS seems to be correcting the lat/lon of the scaled marks. But they don't seem to be using the logs.

 

One of my first recoveries is TU0450. If you look at the GC.com data page which is frozen in time, the coordinates are N 21° 20.833 W 157° 57.700.

 

The latest NGS datasheet the coordinates are N 21 20.850, W 157 57.700. It has moved north about 103 feet but still about 690 feet south of the actual location.

 

Hand held coordinates are N 21° 20.959 W 157° 57.679 which when plotted on Google Earth is about 50 feet west of the actual location. Considering the mark is on the north face of the building those coordinates are probably the best you can get with the wall of the building blocking the signal.

 

TU0626 has also moved about 103 feet north and TU0637 has moved about 99 feet. So there is some corrections being made, but I don’t know how or why. While the corrections are an improvement they are still a long way off, and not always in the same direction.

 

Still need to use the directions to find these marks.

Edited April 10, 2007 by 68-eldo

[Bill93]

I have noticed in the past that the coordinates sometimes looked like someone had followed the to-reach on a more modern map instead of a map from the era when the benchmark was placed. So I was not surprised to learn that the scaled coordinates are a more recent project.

 

A large error is particularly common when a highway number is still in use but has been re-routed. When the coordinates and to-reach don't seem to agree, I have learned to look at the probable route into town in the year the mark was set.

 

I have also seen things where the person in the office had to guess from the information at hand. There is a mark with directions from West street, named because it was the original boundary of the town, but the coordinates appear to have been scaled from the westernmost street in an addition. In the same town, the disk at the base of the water tower has scaled coordinates almost exactly 1 block south and 1 block west of the actual location, about 600 ft error.

 

So use some imagination when things don't add up on the first try.

[+Harry Dolphin]

Scaled coordinates are bad enough. Thank goodness, Andy Bear got you off of the "scaled building numbers".

 

I'm curious if ANY disk in the cluster matched the coordinates--or was even closer than 3/4 mile?

 

Paul

 

We looked at four clusters. For the first, the coordinates got us to the right intersection, and we found four by description. so I did not take any readings.

The second cluster is the one in question.

N 40 50 00 W 74 05 03 Scaled coordinates for all five stations

N 40 49 49.3 W 74 04 43.3 .32 mile off Bolt in utility pole

N 40 49 51.8 W 74 04 41.5 .34 mile off Bolt in utility pole

N 40 49 52.9 W 74 04 41.5 .35 mile off Disk

N 40 49 52.5 W 74 04 38.0 .38 mile off Disk

N 40 49 51.4 W 74 04 38.5 .38 mile off Disk

(Yes. We have bolts in utility poles.)

 

We found three of five in the third cluster. They were off by 199 feet, 243 feet and 422 feet. This I had no problem with.

The fourth cluster, we didn't find any. Paterson Plank Road was rebuilt when the Meadowlands complex was built. The bridge is new (one gone). It is no longer a draw bridege, so the swing gate is gone (two gone). These were obvious, so we didn't bother trying to cross the highway, or find parking on the south side. The WADO transmitter is a restricted zone, so we did not search for it. The one in the concrete pad at the warehouse, we were unable to locate. The one on the steps of the WADO building is missing. There is a fresh patch of concrete on the step (three gone). But the coordinates did get us in the right area.