The Direct Survey Method (DSM) is three-dimensional
trilateration. In this method distance, depth and position measurements are used
to compute the positions of control points and features. Direct
tape measurements are made between control points and features irrespective of
their depth and a relative depth measurement is also required for each point.
This is the main survey method supported by Site Surveyor 2.
Unlike the other techniques this method needs a computer
program to process the measurements. The programs not only calculate the
positions of the points but also calculate how well you know those positions so
you can see immediately whether your survey meets the requirements of the
research design.
Making direct tape measurements between points is much
simpler and more accurate than the alternative, attempting to get a 3D position
from horizontal tape measurements and a plumb bob. A very high degree of
accuracy can be achieved using DSM, this is the most accurate and reliable of
the techniques which use tape measures. A good point position computed using DSM
is accurate to 20mm however this is totally dependent on the accuracy of the
control point network.
