Fig. 34: Cadastral map (block plan showing parcels)
Setting out a building with four local reference points
Once the design has been submitted to the authorities for approval, the new building must be marked out with special poles. The basic form of the building (including projections and re-entrant corners), the shape of the roof (indication of eaves at junction with f acade) and, if required, the outline of any later landscaping must be readily visible.
The structure is set out starting from the boundary points (boundary lines) using the boundary clearance dimensions. A surveyor is usually called in for urban projects these days. He or she will set out the coordinates of the planned structure as calculated in the design office and drive pegs into the ground to indicate the intentions of the planners. This setting-out work takes place based on the permanent control points available from the official surveys.
The data prepared in the design office is loaded into the tacheometer (measuring instrument). The orientation on site depends on the local reference points or the church spires visible. The coordinates are called up on the tacheometer and converted into angles and distances. The tacheometer is set up at a suitable point on the site. At least two local reference points are required to complete the setting-out. The surveyor's assistant with the reflector (reflective staff, to measure distances) approaches the desired point until he or she is just a few centimetres from the target. Instead of the reflector, a peg is then driven into the ground.
GPS (Global Positioning System) methods may be used for setting-out if the horizon is relatively free of obstacles (trees, buildings). In order to calculate the exact lengths of the poles, the surveyor is appointed to determine the ground levels during the setting-out procedure. This normally represents only a little extra work. A height-above -sea-level reference in the vicinity of the new structure is helpful so that the contractor can establish the necessary levels at a later date.
Following the setting-out, the level of the base of the excavation and the angle of the sides of the excavation are determined. The edge of the excavation can be marked with loose gravel or spray paint. The contractor can then commence with the excavation work.
Boundary stone installec
Permanent control point
Boundary stone prior to Installation
Boundary stone installec
Boundary point (pin) in pavement
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