Question Re: Data Sheet

[+osprey46]

If a data sheet reads:

MY0279* NAD 83(1986)- 42 55 04. (N) 070 47 42. (W) SCALED

MY0279* NAVD 88 - 14.109 (meters) 46.29 (feet) ADJUSTED

MY0279 ___________________________________________________________________

 

Does this mean that the adjusted coords are

N42 55 14.109 W070 47 46.29 ?

[2oldfarts (the rockhounders)]

If a data sheet reads:

MY0279* NAD 83(1986)- 42 55 04. (N) 070 47 42. (W) SCALED

MY0279* NAVD 88 - 14.109 (meters) 46.29 (feet) ADJUSTED

MY0279 ___________________________________________________________________

 

Does this mean that the adjusted coords are

N42 55 14.109 W070 47 46.29 ?

 

osprey46

 

The NAVD 88 indicates that the vertical position has been adjusted.

 

The NAD 83 is the long & lat and it is scaled.

 

Hope this helps,

 

John

[+osprey46]

Got it.

 

Thanks for clearing that up for me

[ArtMan]

At the risk of redundancy, and no offense intended, osprey46, if you're way ahead of me on this but:

 

"Scaled" means someone looked at the position on a topo map and measured using the map scale and determined the position that way. No field measurements involved. This technique is used where the benchmark in question is what professionals would really call a "bench mark" — a mark used for elevation (vertical control). Your GPSr won't necessarily take you directly to the mark, though it may be pretty close. Scaled coordinates are nominally +/– six seconds of latitude or longitude, which translates to about +/– 600 feet at middle latitudes, though generally it's considerably more accurate than that.

 

"Adjusted" means that very accurate field measurements have been further improved upon through mathematical methods I don't pretend to understand. Adjusted latitude and longitude are far more accurate than your handheld GPSr.

 

In your example, the given scaled latitude (42 55 04) could represent anything from 42 54 58 to 42 55 10. Most experienced benchmark hunters will use the scaled coordinates to point to the general area, then use the text description to actually find the mark. The descriptions are written (often in the pre-GPS era) to direct you right to the spot. In theory. One of the challenges is that often the area has changed considerably in the years (decades!) since the description is written, so fences have been removed, buildings have changed function or appearance, roads have been realigned, etc.

 

Let us know if you have more questions.

 

–ArtMan–

[TerraVador]

Osprey,

Because MY0279 (GREAT BOARS HEAD 138 RM 1) is a REFERENCE MARK for TRIANGULATION STATION MY0278 (GREAT BOARS HEAD 138), you can calculate the exact coords for MY0279 using the BOX SCORE from the NGS Datasheet :

MY0278* NAD 83(1996)-  42 55 04.48467(N)    070 47 42.16337(W)     ADJUSTED  

MY0278|---------------------------------------------------------------------|
MY0278| PID    Reference Object                     Distance      Geod. Az  |
MY0278|                                                           dddmmss.s |
MY0278| MY5185 HAMPTON BEACH ST PAT CATH CH        APPROX. 1.3 KM 2595444.1 |
MY0278| MY5165 TPA 1943                             86.658 METERS 27835     |
MY0278| MY0279 GREAT BOARS HEAD 138 RM 1            53.605 METERS 27911     |
MY0278| MY5168 GREAT BOARS HEAD STANDPIPE          154.222 METERS 29703     |
MY0278| MY5171 HAMPTON MUNICIPAL STANDPIPE         APPROX. 3.9 KM 3160029.9 |
MY0278| MY0280 GREAT BOARS HEAD 138 RM 2            53.825 METERS 32201     |
MY0278|---------------------------------------------------------------------|

 

Using a program like Geocalc ,you can project a point from MY0278 to MY0279

53.605 meters at an angle of 279 deg 11 min

from coords N42 55 04.48475 W70 47 42.16337.

 

The calculations say MY0279 is at N 42 55 04.74, W 70 47 44.52 ( N 42 55.079, W 70 47.742)

 

You can do the same thing for MY0280 ( GREAT BOARS HEAD 138 RM 2). Its exact coords are

N 42 55 05.88, W 70 47 43.62 (N 42 55.098, W 70 47.727)

[+Black Dog Trackers]

TerraVador -

Using a program like Geocalc ,you can project a point

Hey, that's pretty cool!

 

This situation is a bit odd in that the reference marks are more distant than usual.

Edited August 26, 2005 by Black Dog Trackers

[+BuckBrooke]

It is odd, that the two reference marks are 175 feet from the station, and very close together (roughly the same azimuth angle), instead of close in and angled out. It's very close to the tip of a headland, but not that close...

Edited August 26, 2005 by BuckBrooke

[DaveD]

You can also use the FORWARD program on the NGS "Geodetic Tool Kit" to compute the positions of most RMs -- http://www.ngs.noaa.gov/TOOLS/program_desc...ons.html#InvFwd