POSITION-FIXING 91
Theodolite, electronic distance
measurement, total stations
The theodolite is an optical measuring tool that measures
angles in the horizontal and vertical planes. The theodo-
lite was used in conjunction with chain and tapes for most
surveying practices until electronic distance measurement
(EDM) units were developed. EDMs use infra-red or
laser light to measure distances and they can be attached
or combined with theodolites, enabling distances and
angles to be measured to the same point at the same time.
From this, the ‘total station’ developed. The total station
is a combined theodolite and EDM unit that processes
and stores both sets of data in a microprocessor andBAFigure 11.9 Accuracy of transits: a position fix at A will be more accurate than at B. (Based on original artwork by Ben
Ferrari)
Figure 11.10 Temporary transits formed by setting up paired ranging rods along a shore baseline. When collecting data
close inshore, or on inland waters, additional locational control can be provided by a tape measure or a distance line.
(Based on original artwork by Ben Ferrari.)