A survey point is a fixed, clearly marked point whose coordinates and/or level are known, and to which all measurements on a project are referred. Without one, every dimension on site is an isolated dimension; with one, every dimension can be traced back to the same origin.
What is measured from it
- Level. Heights are referred to a national datum — Ordnance Datum in Britain, NAP in the Netherlands. A benchmark or level bolt nearby is used to set the site datum: the zero level of the project, usually finished ground floor level
- Position. Horizontal position is expressed in a national coordinate grid and set out on site with a total station or GNSS receiver
- Local points. On site itself, points are marked on the profiles, on pegs, with nails in the paving, or in paint on an existing wall
Points to watch
- Always establish at least two, preferably three. With one point you cannot check whether anything has moved; with three you can tell which one has been knocked
- Put them outside the working area. A point in the middle of the future footprint or in the crane’s route will not survive the first week
- Protect and record them. Log each point with a description, level and coordinates, and mark it clearly
- Re-check before every critical stage. Points can settle, particularly after piling, dewatering or bulk excavation
- Monitoring studs. Old buildings sometimes carry survey studs used to track settlement. Never remove these during refurbishment; they belong to records that may run back decades
- One datum, one language. Decide whether dimensions are “above site datum” or “above Ordnance Datum” and use it consistently on every drawing. Confusing the two is one of the oldest and most expensive setting-out mistakes there is
Related terms
- Datum
- Benchmark
- Ground level
- Setting out profiles
- Spirit level
- Surveying
- Ranging rod
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