Geology Reference
In-Depth Information
(a)
(b)
Figure 1.14
Network adjustment. (a) The 1.2-unit misclosure in loop BCFE
suggests a large error in either the 'unsupported' link BC or in BE, the only
link shared with another loop with a large misclosure. (b) Adjustments made
on the assumption that BC was checked and found to be correct but that no
other checks could be made.
extended series of links could include quite large accumulated errors. The
integrity of a system of bases can be assured if they form part of a network in
which each base is linked to at least two others.
Misclosures
are calculated
by summing differences around each loop, with due regard to sign, and
are then reduced to zero by making the smallest possible adjustments to
individual differences. The network in Figure 1.14 is sufficiently simple to
be adjusted by inspection. A more complicated network could be adjusted
by computer, using least-squares or other criteria, but this is not generally
necessary in small-scale surveys.
1.6.4 Selecting base stations
It is important that bases be adequately described and, where possible, per-
manently marked, so that extensions or infills can be linked to previous work
