Benchmarking (also known as benchmark hunting ) is a hobby activity in which participants find benchmarks (also known as survey markers or geodetic control points ). Technically, the term "bench mark" is used only to refer to survey markers pointing to a certain height, but hobbyists often use benchmarks to enter a triangulation station or reference mark. They usually then record their findings online. Like geocaching, this activity became popular since around 1995, driven by the availability of online data on the location of survey signs (with instructions to find it) and by the emergence of hobby-oriented websites.
Many survey markers in the US were set more than 100 years ago. There was also a surge in creating these signs in the US from about 1930 to 1955, along with the expansion of map-making activities across the country. In the US, some of these signs (triangulation stations and GPS points, loosely also referred to as "benchmarks") have precisely "adjusted" coordinates (latitude and longitude). Coordinates "ADJUSTED" are appropriate for sub-centimeter accuracy, while others, usually the actual elevation Bench Marks, have only scaled coordinates from the map. The coordinates of "SCALED" are read from topographic maps, rather than surveyed. Many are accurate up to 100 feet but some are reaching 3,000 or 4,000 feet away from the marks they refer, so the handheld GPS units are not widely used to find them. Most signs have clear descriptions of "to reach", but some lack full descriptions, or changes around buildings, roads, or terrain for decades to make the description obsolete. The mark may have been removed by construction or buried.
Video Benchmarking (geolocating)
Data source on the U.S. mark.
In the US, about 740,000 "benchmarks" with the most appropriate elevations or coordinates (but only a small part of the existing survey mark) are listed in databases managed by the National Geodetic Survey (NGS) and can be accessed on -line. The majority of the signs are set by the US Geological Survey (USGS), the Forest Service, the Engineer Corps, or the city, and the state, and local authorities. Cadastral signs (land surveys) are usually not measured for geodetic databases. The database used by Geocaching.com, the hobbyist website for the US benchmark hunter, is just a "snippet" of a mark documented by the NGS in 2000, and has not been updated since then.
Each NGS registered sign has a permanent identifier (PID) , a six-character code that can be used to call data about that flag. Using forms for internet requests like this, PIDs for marks can be entered and data sheets for the visible signs. The data sheet obtained through a request like this looks like this. There are also websites that use Google Maps to show location marks (and PID) in each state of the US-specific hobby website (such as Geocaching.com) and the Benchmark Hunting forum can provide more information.
Maps Benchmarking (geolocating)
Useful tools
In addition to the survey data sheets for the hunted mark, many hunters carry digital cameras to take close-up shots and areas of survey marks (disks, cross cuts on rocks, old copper bolts, etc.). These photos, as well as the description of the current sign by the person who discovered ("restore") the location of the sign, can then be uploaded to the website as evidence of the find. Surveyors use the term "restore" as a synonym for "finding" signs. This no means that the marks found should be disturbed in any way. On the contrary - disturbing the survey sign even in small ways often damages its usefulness to surveyors and others. In the US, benchmark hunters often file two different reports about the marks they find. One, less formal, made to the website at Geocaching.com. A more formal type is made by more experienced and careful hunters to the NGS database itself, and describes the status found/not found, current conditions, and the latest guidance to achieve it so that others (especially surveyors) can more easily return. find the sign.
Benchmark hunters also often carry a compass (following instructions obtained from the datasheets), probes (like long-bladed screwdrivers) to look for buried signs, shovels (or small shovels) to uncover dull marks, broomsticks (to clear debris) , and one or more of the various length band sizes, are used in recording the reference distance found on the data sheet.
The handheld GPS receiver is often used to get within a few meters of a possible sign error that has adjusted coordinates . Metal detectors are useful for finding signs that have been deeply buried from time to time. The use of multiple tools in combination is sometimes necessary, but many marks are mounted on the sidewalk surface, buildings, walls, stones, or monuments and can often be found without special tools.
Bookmark description
The survey markers vary greatly from country to country. In the US they are usually bronze discs with a diameter of 3.5 inches. Typical discs are slightly inserted into the top of a concrete pillar arranged vertically with a flat surface to the ground or a slight projection. Others are metal rods that are pushed to the ground and may be surrounded by metal or plastic pipe that can be engraved and stamped like a disc. Disks can also be arranged in stone or stone balustrades, and in concrete from large structures such as buildings, bridge buffers, the base of the tower. In the UK, marks are usually carved on walls, or on metal plates mounted on walls.
In the US, survey disks are usually engraved with the name of the agency that puts them. The name of the mark (or "station" it locates) is usually stamped onto its surface, along with a set date (or rearranged, since the destroyed marker can be replaced). Disks marked with triangles are known as "triangulation station disks", as they mark the position of the main point used for triangulation (or mapmaking). Disks marked with arrows are called reference alerts (RMs) , as they point (or "refer") to the main station that may be located a few meters away. Triangulation stations often have two or three reference marks. The reference flag is set to allow the main station to be rebuilt (or reset) if needed.
Sometimes the survey sign is made easier to find by the nearby presence of a witness post , a pole (or small sign) is pushed to the ground and used to draw attention to (and to warn against annoying) Signs.
Care must be taken to ensure that the discs found are described on the data sheet, so as to avoid false reports. Reference flags may be incorrectly reported as station marks. A set of disks in 1945 may be misinterpreted with the same named disk set in 1946 by different agencies, and so on. RESET elevation pegs should not be reported as originals. Sorting these differences and reporting them correctly is an important part of the hobby.
General locations
In the US, markers are often found on mountain tops, along ridge lines, or on the naked edge of the rock with commanding views, since such sites provide a good point of view for the triangulation path to a distant point.
US elevation bench marks are often placed along rail lines or roads that provide a good line of sight for leveling. All the right railroad tracks that are active and partly abandoned are private property, which is actively patrolled by the railway police.
The common location is the upper level of the bridgehead or the wings.
As part of the triangulation network, intersection station is visible. They are high, prominent, and well-defined points like chimneys, spiers of water towers, or church towers. However, many of these objects have been altered or replaced by similar structures nearby and no longer mark their original location, so careful identification is required.
US bench marks are usually placed in public buildings, such as courthouses, post offices, town halls, and old schools.
Benchmarks are often located on private property, or access to them can only be achieved by crossing privately owned land, so permission is required for access.
In the United Kingdom
The British benchmarks tend to be around the corner of pubs, churches and other public buildings, as well as agricultural buildings, railroad bridges, and private homes especially close to the crossroads. However, every building can be used, as well as natural features such as rock outcrops.
In the UK, trigpointing is a recreational activity similar to benchmarking. The search for trigonometric spots is more popular than hunting benchmarks in the UK, but there is a lot of overlap in participation. "Trig points" is the common name for "triangulation pillars". It is a concrete pillar, about 4 feet, used by the Ordnance Survey to determine the exact shape of the country in a project known as British retriangulation, conducted 1936-1962. They are generally located in the highest part of the land in the area, so there is a direct line of sight from one to the next. By arranging the theodolite above the pillar, accurate bearing to the nearest trigon point can be taken. This process is called triangulation.
There are 6550 pillars as listed in the T: UK database. While most of them are not used anymore, about 184 of them are currently used in Passive Station networks. This is maintained so that it can be used as an accurate anchor point for differential GPS comparison, and is researched every five years to calibrate the geological movement of the soil.
See also
- Benchmark (survey)
References
External links
- Yahoo! Groups devoted to studying the triangulation network of Ordnance Surveys.
- The benchmark benchmark section of the Geocaching.com website.
- The UK Live Database benchmark, primarily focuses on flush bracket restrictions
- The English Ordnance Survey source database, was not updated since 1975
- UK Trigpoint Database
- US benchmark overlays on Google Map
- The New England Benchmark Website
Source of the article : Wikipedia
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