Azimuth Marks

[+Klemmer]

I've found (recovered) and logged (mostly on GC.com) about 30 Benchmarks (of various sorts), and probably looked for and NOT found about 30 more. Just to let you know I'm not exactly a newbie, nor an expert.

 

Found / recovered Triangulation Station DX3785 recently (previously recovered most recently in 1975). In addition to the usual Station (Triangulation Mark), and (in this case) 2 Reference Markers, the original description (1939) describes the general location of an Azimuth Marker ("... 1/2 mile NE..."). I guess there is an actual marker there? From the descrption (quite loose), it will not be easy to find, and may not be public accessible.

 

Question: What purpose did / does an Azimuth Station serve? I think I have seen a few references to several somewhere, but not quite as defintely spelled out as this one. Is it necesary for the proper use of the Triangulation Station? In other words, worth looking for? These days, with a survey grade GPS, is one needed?

 

Reference made in the 1939 CGS monumenting entry to a "standard bronze disk set". Does that include a specially marked Azimuth disk? Haven't seen one yet....

 

Look forward to an informative answer (as always in this forum) .........

[+GEO*Trailblazer 1]

I will let the pro's answer it better but my understanding is the AZIMUTH is made with respect to the North Star Polaris and a plumb line.

[Z15]

An azimuth mark is for something for the local surveyors to sight on for bearing determination. You need 2 points on a straight line for bearings and this is the purpose. Without an azimuth mark to use, the surveyor would have to observe the North Star (Polaris) or the sun to determine a bearing for his survey (time consuming and requires special equipment). No bearing means that the survey cannot be legal described or the location known.

 

C&GS set the azimuth marks for use by local surveyors who did not have the resources to use towers to clear the local obstructions (trees etc). There were always visible from the ground (VG) at the station.

Edited December 15, 2003 by elcamino

[+happycycler]

Dusty Jacket has at least one example of an azimuth mark disk on his very helpful web site: http://www.dustyjacket.com/benchmarks.html Please check there for examples of many of the physical objects that we search for.

 

The first azimuth mark that I found happened to have a PID of its own: KLEINSCHMIDT 2 AZ MK There is a photo of the disk in my log. More modern azimuth mark disk photos can be found at: PID=AA8564 Note the letter *A* in the designation -- for Azimuth mark.

Edited December 15, 2003 by happycycler

[+GEO*Trailblazer 1]

Azimuths:

The AZIMUTH of a line is its direction as given by the angle between the meridian and the line measured in a clockwise direction usually from the south branch of the Meridian.

In Astronomical observations Azimuths are generally reconed from the True south;in surveying,some surveyors recon azimuths from the south and some from the north branch of whatever meridian is chosen as a reference,but on any given survey the direction of 0,Zero Azimuth is either always south or always north.

Herin,unless otherwise stated,Azimuths are always reconed from the SOUTH.

AZIMUTHS are called TRUE (Astronomic) azimuths,magnetic azimuths,or assumed Azimuths according as the Meridian is True,Magnetic,or Assumed.

Azimuths have values between 0*-360*

 

Principals of field Astronomy

 

The Azimuth of a line is established by angular observations on some celestial body,most commonly on the Sun or Polaris,The North Star or Pole Star.

For the pupose of computing the AZIMUTH from an Astronomical Observation,it is necessary for the Latitude of the Station be known,also for certian observations it is essential the Longitude be roughly determined.

[+rogbarn]

An azimuth mark is for something for the local surveyors to sight on for bearing determination. You need 2 points on a straight line for bearings and this is the purpose. Without an azimuth mark to use, the surveyor would have to observe the North Star (Polaris) or the sun to determine a bearing for his survey (time consuming and requires special equipment). No bearing means that the survey cannot be legal described or the location known.

 

C&GS set the azimuth marks for use by local surveyors who did not have the resources to use towers to clear the local obstructions (trees etc). There were always visible from the ground (VG) at the station.

I have seen many answers to this question on several threads over the past year or so. This is, by far, the best, most easily understandable answer about what it is and why it is there. Thanks elcamino!

[+gnbrotz]

Since the "What are they?" part has been answered quite extensively by those more knowledgeable about those things than I, I'll stick to the "Where are they?" part.

 

As you've already noted, the description for actually locating an azimuth mark can be quite vague. I do try to locate them when hunting triangulation stations, and have had pretty good success (read "luck"). There is one good solid piece of information you can use, but you have to know where to look to get it, because it's not included on the regular benchmark page.

 

If you click "View original datasheet" link on the benchmark page, it will allow you to do just that. The original datasheet contains some "extra" information, which IMO, makes a complete station recovery easier.

 

Just down from the top a bit, you'll find a list, enclosed in a box, which lists various other references in relation to the station itself. This list includes, but is not always limited to, the reference marks and the azimuth mark.

 

For the reference marks, it will list a distance (in meters) and a (true) bearing from the station. For the azimuth mark, it does not list a distance, but does provide the bearing.

 

Using this information, I project a line at the proper bearing, which will pass through the AZ mark being sought. From there, you can add in any other clues the description may provide, such as how to get to the mark from the station, its distance from the edge of the road, or any other useful information.

 

If you take some time to go through this thread, you can see my process.

 

I've already begun similar research on the station you mentioned and when I make a conclusion (read "guess") I'll drop you a note.

 

*edited typo

Edited December 15, 2003 by gnbrotz

[+gnbrotz]

If you are able to obtain permission/access, try looking in this area:

 

N 33° 31.807

W 117° 15.383

[DaveD]

As Elcamino noted, Azimuth Marks were set to provide surveyors with a point of direction (azimuth) to begin and/or end their surveys. As GEO*Trailblazer 1 noted, azimuths used to be oriented to the south end of the meridian. In response to an overwhelming number of requests for the surveying community, NGS changed the orientation for azimuths to North when we published the North American Datum of 1983 (NAD 83). In the vast majority of cases the observation of the azimuth mark was carried along as part of the normal process of triangulation. Only at certain strategic spots would astronomic (Polaris) azimuths be observed. Astronomic azimuths require critical computation of the LaPlace correction which accounts for the deviation between the surveyor’s instrument being plumb to the local attraction of gravity, and not normal to the mathematical ellipsoid model of the Earth used in the computation of latitude and longitude. The standard procedure was to set the azimuth mark at least ¼ mile away from the primary station to ensure a good pointing by the surveyors theodolite/transit. Prior to the development of low cost electronic distance measuring equipment in the early 1970’s it was not common to measure the distance to the azimuth mark because of the effort and expense required to perform the

[+Klemmer]

Thanks to all ! My question answered very well indeed. As I've said before - best forum on GC.com! Happy Holidays and Happy BM hunting.

[+Tall Guy]

i might just add my military perspective. in ROTC training we learned to navigate at night, without lights, with only a compass and map (and a red light flash light). Its really fun when it's snowing but anyway... Basically the best way i can describe an azmuth is a straight line between two points, as another 'cacher mentioned already.

 

the way we use azmuths is we get to a known location (we use the military decrypted GPS so anyway, once you know where u are exactly on the map, (the give u the grid coords for the starting point), you shoot an azimuth. this means you figure the location of your next objective with a map and protracter and then look through the sight line in the compass towards that location, and off you go.

 

when you approach the azimuth its likely you'll get off course so its important to keep an eye on a reference. just like the GPS does when you get off course (like theres a bldg in the way.

 

hope this is helpful. It's an awesome time running around the woods on a base with only the little we had and the light of the moon. We found all 7 assigned locations without GPS in just 2 hrs in an area on a mountain side a few miles square.

 

surveyors just shoot the azimuth to one of the already established reference points and using maps they can tell exactly where other points should be by measureing distance and angles (we used pace counts talk about inacurate)

 

... happy hunting, hope this helps.