Volume 6 – Geotechnical Manual, Site Investigation and Engineering ...

Chapter 1 GEOMATICS AND LAND SURVEY SERVICES
1.5.4 Economy and Accuracy
It is important, before any field survey operation is started, to weigh the accuracy against the time,
resources and costs. The greater the accuracy required, the greater the cost of operation. Since
accuracy depends upon the elimination or reduction of errors, it is essential that the surveyor
understands the nature of the errors and plans his works in such a way to reduce them to acceptable
levels to meet the misclosure tolerances adopted.
1.5.5 The Independent Check
In every survey operation it is the responsibility of a surveyor to do a check. It is best to employ a
system which is completely self checking. Where this is not possible the check applied should be as
independent as possible and not just a repetition of the previous operation. For example, if the
measurement of the length is carried out, the check applied should be made by measuring the
distance again using different unit of length or measuring in the reverse direction. In many cases a
rough check is very useful and sometime all that is required. Computations which are not self
checking should be completed by another survey staff including, using, if possible, methods other
than those used.
1.5.6 Safeguarding
Marks established by the field surveyor for the horizontal and vertical control framework should be as
permanent as possible or easily re-established from nearby marks. Liaison with Agricultural
Department may be considered during planning for topographical surveys to coordinate simultaneous
concurrent activities to collect water and soil test samples to determine their suitability for crop
cultivation. Hydrological stations for systematic collection of data such as rainfall, stream flow,
maximum flood levels, tidal range, etc. should also be considered.
1-4 March 2009