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Benchmark use in Current Surveying


WingArcher
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Hey Survey Tech, you out there? I just saw a survey crew with a tripod over a benchmark in my town, and I wonder... I know that the UGS datasheets are fairly particular about where benchmarks are located, some more so than others. My question is how they are most often used now. My guess is that property lines and such are defined more in relation to local landmarks and other properties than defined as a set of coordinate points (pick your system!) in a global grid. So do benchmarks get used as a convienent point of reference (so many feet from such and such) in local surveys? Is the altitude information from the datasheet used as well to determine slopes and so forth? Both? It appears too that a lot of benchmarks are used for neither anymore.

TIA for any info you may have.

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At a minimum, most of the Bench Marks are still used for elevation purposes. Some of the marks you see are horizontal control, or azimuth marks, with a scaled elevation. I would say these monuments are getting used more now than ever before. A lot of the surveying is being done by GPS, and these "Bench Marks" have known coordinates from which you can reference the survey. The published lat/long coordinate is coverted to the State Plane coordinate system for the purpose of the survey.

Hardly a week goes by that I don't have to hunt up one of these monuments, for one reason or another, to survey some piece of property.

 

"True Grid"

In the Pacific Northwet

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WingArcher

Yes, any marker that remains undisturbed is still quite useful. Some are likely to be used more often than others, depending on how convenient their location is, but they all retain their value as long as they are not moved, and they should all be preserved.

You are right about property lines. Most of the markers you have information on are not property corners, but some are. Surveyors determine property line locations using all available evidence, including recorded public information, such as deeds, and maps, as well as the objects they find marking other property corners near the piece of property they are surveying. So, they do, as you say, make sure that each property they survey is correctly related to the surrounding properties in the area.

The markers set by the United States Coast and Geodetic Survey, and its successor the National Geodetic Survey, as well as the United States Geological Survey, are intended primarily to facilitate mapping and commerce, rather than boundary determination, and have been instrumental in the development of our economy. The network of Triangulation Stations, which covers the nation, provides horizontal control for mapping, allowing local professionals to determine the precise position on earth of the objects they are mapping, by measurements from the Tri-station. Thay are also used in the design and layout of such large scale construction projects as interstate highways, railways, pipelines, power transmission lines and government installations, to position these objects in the right location. The network of Benchmarks, also nationwide, provides vertical control, also known as elevation or altitude, for the same purposes. Through the use of Benchmarks, surveyors determine the elevation of existing objects, which is essential to construction design. Then they use them again, later in the process of construction, to layout the objects being built at the correct elevation, which is shown on the construction plans.

I would recommend that you, and everyone else in geocaching for that matter, try to meet someone who works in the Land Surveying profession in your area. They could explain the use of these markers to you in greater detail and give you specific examples of how they are used in that area. In return, you can be of assistance to them by sharing your findings with them, informing them of the status of any markers you look for in the area. I think it might prove to be a rewarding learning experience.

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