Category: Surveying
Surveying Worked example in setting out
The purpose of conducting a traverse of the type described in Appendix E would typically be to establish additional local control points, in order to set out specified points for construction work. Suppose now that it is required to set out a foundation point X at the co-ordinates (544,850.000E, 257,200.000N) to high accuracy. The accepted…
Surveying Worked examples in adjustment
E.1 Bowditch adjustment This example shows how the Bowditch calculation sheet, introduced in Chapter 10, is used in a simple traverse to fix the positions of two unknown points (C and D, in Figure E.1). The scheme of observations is as shown in Figure E.1, with stations A, B, E and F having known co-ordinates.…
Calculation of local scale factors in transverse Mercator projections
D.1 Quick calculation The quick formula for calculating a scale factor is: where S0 is the central scale factor, E0 the false easting of the true origin and RE the mean radius of the earth. This formula is accurate to 2 parts per million at all places within 200 km of the central meridian, and…
Surveying Worked example in transforming between ellipsoids
This example shows how the geographical co-ordinates of a station can be converted from one system to another, following the method given in Section 8.4. In this case, the initial co-ordinates are quoted in the ETRS89 system, so are based on the WGS84 ellipsoid; and they are to be converted to the Airy ellipsoid, whose…
Reciprocal vertical angles
The height differences between control points are often explicitly required in engineering surveying work. Even when they are not, they must (for instance) be found before distance measurements can be used in accurate surveying work, as shown in Chapter 11. The methods for measuring height differences covered earlier in this book are levelling (for short…
Reduction of distance measurements
The reduction of distance measurements means the process of converting a measured slope distance between two points to the reduced distance over the ellipsoid between the projections of the two points onto the ellipsoid. It is useful to start by thinking of the simple geometry which would arise if the earth were flat, as shown…
Adjustment of observations
10.1 Introduction The term adjustment suggests that some form of cheating might take place during the process of converting surveying observations into results. This is not necessarily the case. As explained in Chapter 2, surveying observations always have two particular properties: 1 they contain errors (random, systematic and the occasional gross error); 2 the system…
