What's the difference between bench marks and control points?
What's the difference between bench marks and control points?
(OP)
What's the difference between bench marks and control points?
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What's the difference between bench marks and control points?
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What's the difference between bench marks and control points?What's the difference between bench marks and control points?(OP)
What's the difference between bench marks and control points?
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RE: What's the difference between bench marks and control points?
RE: What's the difference between bench marks and control points?
RE: What's the difference between bench marks and control points?
RE: What's the difference between bench marks and control points?
RE: What's the difference between bench marks and control points?
Maps will give you your horizontal position but not your height (you can interpret between contours but not accurately).
In UK bench Marks are located by the Ordnance Survey on solid structures etc at frequencies of about 1/2 mile and are shown on maps. When doing preliminary work such as locating pipelines it is easy to establish your horizontal position on a map but impossible to establish your vertical height hence the need for bench marks. You can simply make a reconnaissance survey of a utility route by following a line on a map and running a string of levels. By tying the levels into bench marks along the line you get a check on accuracy. I guess mapping in the US also includes bench marks. Often in UK setting out of utilities is made from existing features without the need for accurate horizontal control.
As Sam says when you first establish a site you bring in the surveyors to set up 2 or 3 control points for horizontal control. Once you have set out the plan it is fixed for the job but you need vertical control for everything from setting drain falls to roof slopes. So you set up bench marks around the job and check them for settlement etc at intervals against permanent bench marks established outside of the site.
RE: What's the difference between bench marks and control points?