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Correct Term for Disk's Observed Point?

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Cool. That sounds even better... :)


By the way, I passed by Halibut Pt. last week while hunting in Rockport and bumped into my State Park friend. He inquired hopefully about whether he would see you before the snow flies. I said I didn't think so, but maybe in the Spring... :D Turns out they were impressed with my "find" of RM2 and now look fondly upon this business. You will love getting a tour of the fire control tower...



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Here is the definition for “mark” from the NGS GEODETIC GLOSSARY (not on-line):


mark - (1) A dot, the intersection of a pair of crossed lines, or any other physical point corresponding to a point in a survey. The physical point to which distances, elevations, heights or other coordinates refer.

(2) The object (such as an incised or stamped metallic disk) on which the mark (1) is placed.

(3) The entire monument, consisting of the mark (1), the object on which it occurs (2) and the structure to which the object is fastened.

(4) In hydrography, the term is sometimes used for water mark.


So, I would simply call the “+” on a disk, the mark.


Different groups in the surveying profession use different names for the same thing. For example some surveyors call survey disks, “caps” or “markers”. Most on this GC site call all survey marks, “bench marks”, and so on. The one that I guess really bothers me is calling a tower a “bench mark”. Almost all the many towers in the NGS database (church spires, radio masts, lighthouses, tall buildings, water and oil tanks, etc.) were positioned using the “intersection” method and are called “intersection stations”. The intersection method is usually done by observing directions to the same point on the tower from three or more known locations. Two directions provide a position and the third provides a check. A few intersection stations have been positioned by “traverse” or some other survey means.


Two more definitions from the “Geodetic Glossary” follow:


intersection - (geodesy) Determining the position of an unoccupied station as the intersection of two lines drawn with specified directions from two other stations of known location.


bench mark - A relatively permanent, natural or artificial, material object bearing a marked point whose elevation above or below an adopted surface (datum) is known. Sometimes written "benchmark". Usually designated a BM, such a mark is sometimes further qualified as a permanent bench mark to distinguish it from a temporary bench mark.


More information on “Intersection Stations”, from USC&GS Special Publication #247, “Manual of Geodetic Triangulation” (at: http://docs.lib.noaa.gov/rescue/cgs_specpu...47rev1959.pdf):


Page 4:

13. Intersection stations.-As many prominent objects as possible, such as church spires, water tanks, standpipes, towers, beacons, tall chimneys, and prominent mountain peaks, should be selected as intersection stations. The three most suitable occupied stations from which the intersection stations are to be observed should be indicated by short rays from the intersection station’s symbol on the reconnaissance sketch.


Page 13:

12. Intersection stations.-At each occupied first-order or modified second-order station, directions will be taken (with four positions, using first-order theodolites) on objects such as church spires, water tanks, towers, standpipes, lighthouses, prominent mountain peaks, and tall chimneys.


Page 106:

Observations on intersection points are desired from three stations if possible in order to obtain a check, but observations from two stations will be acceptable if the pointings are carefully identified. Wherever there is any choice, the nearest occupied stations which will give the best intersection should be used. Observations from the nearest stations are desirable in order that distances from them to the intersection stations may be based on direct observations. When an intersection station is within a short distance of an occupied station, the distance should be taped. Observations on an intersection station from more than three of the nearest and most suitable occupied stations are not necessary unless the object is visible from the ground. All such objects should be observed for azimuth purposes at all stations at which they are visible from the ground, regardless of whether they can be intersected from other stations or not. Observers should be constantly on the alert, for all possible additional intersection stations, and should not limit their observations to objects that are shown on the reconnaissance sketch.


The same name for an object is used by all units, although only one person need visit the intersection station to write the description. A daily informal conference in camp between the observers and computers is helpful. On some parties in areas where intersection stations are numerous, one man (usually the assistant computer) is designated to canvass the area in advance of the observing, and select and write descriptions of the intersection stations. These are discussed with the observers, and scaled angles with correct names assigned are given to each observing unit prior to observing. After observations are completed the assistant computer draws a graphic plot of the observed cuts to intersection stations, which serves as a check on identity of the object and the number of suitable cuts. The basis of this temporary plot can be a sketch to any convenient scale on blank drawing or chart paper with the occupied stations plotted by computed distances taken from the preliminary triangle computations.


Page 123:

The height above the ground of prominent intersection stations, such as radio masts, in excess of 250 feet in height, should be determined to within the nearest five feet. This can sometimes be done from an adjacent occupied station by observing the zenith distances of the base and the highest point of the object. Special trips should be made to intersection stations by one of the observing parties designated by the chief of party for the purpose of obtaining the above information whenever it cannot be obtained in the regular trips to and from camp.




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Mutter, mutter, mutter.....


Thanks, George!--


I generally use the term "mark" to mean "disk" (or bolt, or iron bar, etc.)--the immediate setting of the point referred to. I hope this is OK. Sometimes I find that I need to refer to the little countersunk hole (or crossing point) that marks the "physical point referred to" on a disk (usually to say that it survives after a disk has been vandalized). So I'm looking for a word that is not "disk" for that. :blink:


Is "datum point" (which has an alluring Latin sound to it) OK for my use? I would then like to know how many angels can dance on a datum point....




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Klemmer, that reminds me of the time in 1982 when I mentioned a 6SN7 to an electrical engineer and he didn't even recognize that it was a vacuum tube number, much less know that it was a twin triode. And that was 26 years ago.


Or last month at our writers group, a young lady presented a story that was set in 1947 and had the army suppressing information about a flying saucer. The line that got me was "search the crowd for cameras or hidden recording devices" as if there was a recording device in 1947 that could be hidden on one's person.


Makes me feel old.

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