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Possible Error?


Spoo

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I have tried to find the Azimuth mark for a year and through a couple or three attempts, for OC2620, ANDREA. No luck. Here is the description for the Azimuth mark, OC2618:

 

OC2620'

OC2620'THE AZIMUTH MARK, STAMPED---ANDREA 1976---, IS A STANDARD

OC2620'DISK SET FLUSH IN A DRILL HOLE IN EXPOSED BEDROCK.

OC2620'IT IS 3.0 FEET WEST OF A METAL WITNESS POST, 25.3 FEET NORTH

OC2620'OF POWER POLE NUMBER 21 AND 33.0 FEET NORTHEAST OF THE

OC2620'CENTERLINE OF THE ROAD.

OC2620'

OC2620'THE HEIGHT OF THE LIGHT ABOVE THE STATION WAS 1.37 METERS.

OC2620'

 

Today, out of stubbornness, I tried again even though I had already reported to the world that I could not find it. Of course, I found it. The Winess Post has been uprooted and tossed aside and the center of the road .....is WHERE? The Pole and the bedrock were my only clues and the bedrock all had about an inch of dirt on it. The bedrock here, exposed, is probably 50' x 100'.

 

These survey reports are supposed to be indicating TRUE north.....therefore, when the report above says NORTH of the pole, I ADDED ABOUT 18 degrees to my compass...just a good rough number of declination for this neck of the woods.......I even looked in the magnetic north direction........

 

Today I found it at Magnetic North MINUS about 18 degrees !!!

 

There is NO WAY the pole was moved. It is a very old line of poles and to get the NORTH indication to the disc would have put the pole in bedrock also.

 

A mistake by the surveyor?

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Mistake, they never make mistakes. Check your compass. LOL

 

These survey reports are supposed to be indicating TRUE north

 

No, they would have used a compass so it would be magnetic North in the descrption, not true North. The recon team picks the location, builds the monuments and writes the description. Probably just a 1 or 2 man operation....

 

18° declination? Around here is iron ore county and 1° would be a lot

Edited by Z15
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I'll let some one else chime in here about whether this is true or magnetic north in the description. My understanding is that the NUMERICAL values listed are always in TRUE north. I do not know about this written statement.

 

But even then, there is an 18 degree error.

 

True north runs 16-18 degrees EAST of mag north here in my neck of the woods.

 

And trust ME. I know my equipment....my compass is fine.

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It seems to me when named directions are given in the descriptions, with no numerical bearing, they are often given to the nearest of 8 directions, e.g. NW, and never to finer than NNW. I would guess they are sometimes eyeballed without carefully sighting over a compass, especially when the distance is short. So I wouldn't have been surprised by 18 degree difference.

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I'm agnostic as to whether text descriptions refer to true or magnetic north, but I rarely see descriptions to nearby objects more precise than, e.g., NW or SE, so "north" in the text could be anything +/- 22.5 degrees from whichever "north" we're working with. Either way, in your case it would see that "north" is a better description than "northeast" (or "northwest").

 

The important thing, though, is that you found the thing. And after so many failures. I admire your persistence.

 

-ArtMan-

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Spoo,

 

They called North out as a Cardinal Direction so you can't expect too much more from that.

 

Had you wanted to nail it tighter, The Box Score would have helped you.

 

OC2620|---------------------------------------------------------------------|

OC2620| PID Reference Object Distance Geod. Az |

OC2620| dddmmss.s |

OC2620| OC2618 ANDREA AZ MK 365.663 METERS 09222 |

OC2620| OC2619 ANDREA RM 1 22.276 METERS 12607 |

OC2620| CE7187 ANDREA RM 2 21.178 METERS 23622 |

OC2620|---------------------------------------------------------------------|

 

Best Regards,

 

Rob

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Alas........

 

I lack the equipment and the talent to measure an angle that tight over that distance.

 

I tried to do a reverse azimuth on the station but lacking the accuracy and looking in the wrong direction off the pole, it did not help me.

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FYi

 

Info on Descriptions..I notice a few things did not scan as correctly hopefully it still can be understood...

 

5. DESCRIPTIONS

 

Descriptions are an importatnt product of geodetic leveling because the utility of the vertical control network depend~ largely on how effectively thev facilitate bench mark recovery. Consult the .NOAA Manual, Geodetic leveling" (Berry 1978).  in preparation at the time of this writing. for detailed instructions on how to write descriptions.  If this is not available, Special PubHcalion ~o. 239, Manual of geodetic leveling (Rappleyc 1948), also contains some valid information. General guidance for deJIcribing a monument is given here.  In NGS, geodetic data. including descriptions, are ~tored, manipulated, retrieved, and sometimes disseminated by computer. Consequently, descriptions must be submitted in proper computerreadable form for inclusion with NGS vertical control data. Consult chapter 7 of Input Formats and Specifications for the NGS Data Base (NOAA 1977) for acceptable format.  The text of the description provides information needed to loute a bench mark. It must be clear and concise, fi{'St  leading the reader to the general vicinity of the monument. then to the exact spot.  Directions :should start from a highway interijcclion or prominent landmark in the nearest  city shown on an official state highway map.

Unless the bench mark is very near the starting point, distances are first given to the neare:st tenth of a mile (or kilometer). The nearer the monument is approached, the

more refined the measurements become, going from miles and tenths. to tenths of a mile, to feet and tenths (01' kilometers and tent hs, to tenths of a kilometer, to meters and tenths). As a rule, give distances in order of decreasing magnitude, but the final reference measurements should be made in the order which lends most conveniently to recovery. For ~xample, if a monument is located 2.6 meters from the corner of a building and 5.4 meters from a fence, it should be 5tated in that order because the building would be spotted first.  Distances must usually be accompanied by directions to 8 poi nts of the compass (i.e., north, northeast, east. . .). Where confusion could result with only 8 poi nts, 16 poi nb of the compass may be used (i.e., east, east-southeast, southeasl. . . ).  Do not record numeric data with more significant digits than those with which the)' were ob-tained.  The number 2.90 doe!! not imply the same meaning as the number 2.9. The former refers lo a value between 2.895 and 2.905, which is accurate to the nearest hundredth of a unit. The latter refers to a ~-alue between 2.85 and 2.95, accurate only to the nearest tenth.

All bench mltrks to be included in the national network must be referenced with consistent techniques, or misinterpretation of some description!' will result. Distances

between reference objecLs and monument!1 should nearly always he-measured horizontally or mathematically reduced to a horizontal distance. In special circumstances where great convenience results, a sloped distance may be recorded in the description. but it must be labeled al3 such. Distances not labeled as "sloped" are always assumed to be horizontal. For an angle of 30c, the difference between a horizontal distance of 10 meters and its sloped counterpart is more than a meter. A dil3crepancy of this magnitude can result in considerable 1085 of time when searching foT II buried monument, expecial]y if the lines-or-position intersect at a shallow angle as shown in figure 2 (page 8). Furthermore, a distance measured from a line, such as a fenceline or centerli ne, should always be measured perpendicularly to that Ii De. The origins of measurements mu~t be deitrly defined in all cases except the following two, where by convention they are inferred. (1) ,\l the junction of two or more roads, the origin will be assumed to be the intersection of the centers of the roads unless specificall)' defined otherwise. "The intersection of U.S. Highway 29 and State Road 120" means the intersection of their center~- (2) Measurements are assumed to be from the center of objects such as utility poles. Where another position is desired for the starting point, it should be noted (e.g., "4.5 meters southea~t ot' the southeast edge of telephone pole number 258").

Good descriptions are very important. Some bench marks are not recovered and used for many years after they are set. During this time hea~-y vegetation can grow tip around the monument, maki ng recovery difficult and ti me consumi ng.

Objects used as reference points can be moved or destroyed. Good judgment and foresight are needed in referencing the mark and writing thc des(~ription.

Edited by Z15
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I have an example where the azimuth is described as some distance south of a fire hydrant, in fact it is north. There were other factual problems (although not as important) with the description of that PID and I've always meant to go back and write my own description. I just figured it was carelessness on the part of the writer and/or typist.

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I also haven't found a lot of accuracy in the bearings of to-reach instructions. I have often wondered whether they are supposed to be magnetic north or true north based. Z15 has answered this - the recon team writing the to-reach would be using a magnetic compass. I don't like 8-point compass readings and will often use 16-point notation if I re-write a to-reach.

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OK...it's now as clear as Mothers' milk..........

 

Numerical data is True North. Written statement descriptions are in local Magnetic North, using 8 point compass readings with an acceptable error of +/- 22.5 degrees.

 

Interesting.

 

(but then, that's what makes this FUN and EXCITING !)

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