Geological Survey (USGS)-7.5 minute quad name follows. The PID is also found all along the left side of each data sheet record and is always two upper case letters followed by four numbers. Either of these may be used to search for the station in the NGS database. This is followed by the station’s designation, which is its name, and its Point Identification, PID. There are several, and among them are Continuously Operating Reference Station, Federal Base Network Control Station, and Cooperative Base Network Control Station. Then the station’s category is indicated. The first line of each data sheet includes the retrieval date. In addition to the latitude and longitude, the published data include the state plane coordinates in the appropriate zones. There is a good deal of information about the passive survey monuments on each individual sheet. That utilization should be informed by an understanding of the datasheet that accompanies each station and is easily available online. They can provide reliable control when properly utilized. Monuments that are the physical manifestation of the National Spatial Reference System (NSRS) and can be occupied with survey equipment are known as passive marks. These sheets have a great deal of excellent information concerning the coordinates, the quality, and many of the details about existing control points that can be used as checkpoints in any GPS/GNSS survey. You can retrieve sheets that are similar to what you see in the illustration. Brass tablets and brass caps have been set around the United States by the National Geodetic Survey also known as passive marks. Each bronze marker was mounted atop a rather large (concrete base = the top surface of the base would have probably been less inches (+_), and extended well over 12″ above the ground! I was/am somewhat familiar with some of the local round ‘Bronze Bench Marks’ that in most cases are only a few inches above the ground surface.One of the things that is very useful is understanding the existing control that is currently available. Many, many years ago, a good friend of mine (now deceased) invited me to accompany him to a rather remote (over-grown) area on his property (very near a ‘County Line’ in S.C.) for the expressed purpose to view three seldom seen brass/bronze “bench marks” that formed a triad of approx. Azimuth marks, coupled with its triangulation station, provides a compass direction of the true north (which is different from the magnetic north). Reference marks help keep triangulation stations from being lost with arrows on their disks pointing in the direction of their referenced triangulation station. TRIANGULATION STATIONS are markers with positions determined by measuring distances and angles from other stations. These points can be observed with a telescope using trigonometry to determine their position on Earth. Examples of intersection stations are water or radio towers. INTERSECTION STATIONS are horizontal control marks with landmarks that can be seen from a distance. Within these two broad types of survey benchmarks, there are different types of categories for horizontal control markers as described in NOAA’s Horizontal Control documentation. Horizontal control points simply contain latitude and longitude values.Vertical control points contain a precisely measured orthometric height that is measured as height above sea level.Two main types of benchmarks exist – “vertical control points” and “horizontal control points”. Benchmarks are important to surveyors because they help accurately measure the positions of all land boundaries and modern infrastructure. It makes it possible for greater precision for surveys and to locate national, state, county, and private boundaries with greater precision. Horizontal control data provide a rigid framework for map makers, engineers, and land surveyors in North America. Geodetic leveling can help understand the area and volume of the Earth. With 2 benchmark locations, surveyors use triangulation and trigonometry to measure the direction, distance, and elevation between them. They serve as a basis for North America’s horizontal control data. This is why geodesists developed the geodetic survey network extending across North America. In surveying and mapping of large areas, surveyors must take into consideration the curvature of the surface of the Earth and sea-level surface. More recently, surveyors use markers to set up a GPS receiver antenna in a known position for Differential GPS surveying.
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