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What is a ordnance Survey Bench Mark?
An Ordnance Survey Bench mark (BM) is a survey mark made by the Ordnance Survey to record height above the Ordnance Datum.
What is datum in land survey?
A land survey datum (plural datums) is a reference from which measurements are made. The reference in the form of a set of coodinate and a direction. The datum can be arbitary (assumed) or absolute. The arbitary datum point is a point whose coordinate and direction are not known, so an arbitary value is adopted. All other coodinates of the survey project are connected together, but its datum point is not connected to a larger network. The absolute datum is a reference point whose coordinate and direction are already known within a frame of network. So the new survey become part of the network.
Datum to start survey in land survey?
The datum you start a land survey in will depend on the purpose of the survey, where in the world you are, and what type of instrument you are using. If the purpose of the survey was for your own purposes and there was no need to have the survey in terms of any local, national or international datums then a surveyor would usually do the survey in a local datum. A local datum is where the surveyor sets up a local control network (where all the locations the instrument is set up) and they either do not connect to a local datum or they do not worry about the local bearings and coordinates. If the purpose of the survey requires to link into your local services (sewers, water, etc) then the levels and positions will need to be in terms of the local network (or networks). In some locations the level datum is in metres (or feet) above sea level, in other locations it may be 100 metres (or feet) above to avoid some elevations being below sea level (the old systems could not cope with negative numbers). Every country has a set of different local and national datums. Take New Zealand for example, the national datums are NZGD 2000, NZMG plus 29 local circuits (with 2 different versions. Australia has around 18 local circuits with some having 2 - 3 different versions. The UK has the UK National Grid and UK UTM zones. Ireland has the Irish National Grid. And the list can go on. The type of instrument you are using can also influence the datum you use. GPS for instance does all its calculations using WGS84 and then you can request it to display the results in the relevant local datum.
What is reduced level in land survey?
A reduced level is the vertical distance between a survey point and the adopted level datum. There are two methods for calculating reduced levels, namely the "rise and fall" method and the "height of collimation" method. The latter reduces levels relative to the instrument height. As it has inferior built-in checks, it is unreliable.
When sampling is more appropriate than a census?
Yes. A sample only provides data from some of the population and is then extrapolated to the whole population; this assumes that the sample is taken equally from all possible datum points across the population - this cannot be guaranteed. A census provides data from all of the population so it is 100% as accurate as the data reading - whether the data collected is accurate or not depends upon what the data is and how it is obtained.
In a building plan what does 1.27 meters AOD mean?
above ordnance datum!
What is a ordnance Survey Bench Mark?
An Ordnance Survey Bench mark (BM) is a survey mark made by the Ordnance Survey to record height above the Ordnance Datum.
What is the highest motorway in UK?
The highest motorway in the UK is the M62 near the boundry between Yorkshire and Lancashire which reaches 372 metres (above ordnance datum)at it's peak. == ==
How can you describe how far an object is from sea level?
Sea level rises and falls, so a datum line was put by the British Ordnance Survey on a harbour wall at Newlyn, Cornwall. It is from this datum line that mean sea level is measured.
What is AHD in surveying?
AHD stands for Australian Height Datum, which is a reference system used in surveying to measure heights and elevations. It is commonly used in Australia to establish consistent vertical measurements across different locations.
What is Land Surface Datum?
Land-surface datum is a datum plane that is approximately at land surface at each well. If known, the elevation of the land-surface datum above sea level is given... Datum: any level surface, line, or point used as a reference in measuring elevations.
What is the definition of 'datum' surfaces?
any level surface from which vertical distances of the points above or below this surface are measured is known as datum
What does RL in terms of elevation stand for?
RL stands for Reduced Level in terms of elevation. It refers to the height of a point or feature above a chosen reference point, usually a specified datum or benchmark. RL is commonly used in surveying, construction, and engineering to describe vertical measurements.
How do you convert a level expressed as Ordnance Datum Liverpool to Ordnance Datum Newlyn?
Take a look at this Ordanance Survey page. http://benchmarks.ordnancesurvey.co.uk/pls/htmldb/f?p=111:7:6255072357299077241::NO:7:: Type in a kilometer square grid in the form "SP9013" for instance. This page will give you a conversion factor. It seems a little ambiguous as to whether the figure they give you is to convert Newlyn to Liverpool or vica versa. I am still investigating.
What does ordnance survey map mean?
Ordnance survey maps are maps that show altitude in relation to a 'known' ordnance datum. An ordnance datum is a point of particular altitude. In the UK, that ordnance datum for ordnance survey maps is the mean sea level at Newlyn in Cornwall. Ordnance survey maps typically show topography, by means of contour lines and spot heights. General land detail, such as grass-land, forest, marsh. In addition roadways, railways, footpaths and bridleways are shown. This makes ordnance survey maps of particular use for anyone wishing to navigate on foot. And this remains one of the most popular uses for this type of map. Ordnance survey maps are maps that show altitude in relation to a 'known' ordnance datum. An ordnance datum is a point of particular altitude. In the UK, that ordnance datum for ordnance survey maps is the mean sea level at Newlyn in Cornwall. Ordnance survey maps typically show topography, by means of contour lines and spot heights. General land detail, such as grass-land, forest, marsh. In addition roadways, railways, footpaths and bridleways are shown. This makes ordnance survey maps of particular use for anyone wishing to navigate on foot. And this remains one of the most popular uses for this type of map.
What is the bench mark?
It is a fixed reference point whose elevation above a given datum line
What does reduced level mean?
In the context of Civil Engineering, especially land surveying, Reduced Level "RL" refers to reducing (or equating) levels (elevations) to a common datum, which is either a real or imaginary location with a nominated elevation of zero. The most common convenient datum was mean sea level. On small surveys that require the collection of elevation data the datum can be assumed and for practical purposes it simply needs to be far enough below the survey area to avoid negative numbers, thus the starting point of a survey might be nominated to be RL 100.00
