Network Design FAQs
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How "good" must the approximate geodetic coordinate positions be for effective Network Design (Pre-Analysis)?
The answer depends on the size of your network; more specifically, the length of each network leg. The approximate coordinates must be accurate enough to
reflect the geometry on the ground. Good network geometry is critical to
good adjustments and effective outlier detection. For network design, you
must provide three things: the proposed network geometry; the types and
frequency of observations; and the expected precision with which you
expect to measure these observations. The approximate coordinates will
satisfy the first requirement.
For example: You occupy Station A and measure a chord
distance to Station B. If the stations are said to be only 100.0 meters
apart in design (based on the approximate coordinates you have
provided), then an expected precision (or standard deviation) of 0.05m
may look OK in design, but would be considered unacceptable (1:2000) for
a high-accuracy survey. This blunder would show up in network adjustment.
On the other hand, if the two stations were actually 10,000.00 meters apart
(1:200000) and you represented them as such in design, your future
adjustment will likely deliver the expected results you modelled during
design. This same logic can be applied to all observation types.
In general, the closer the three components are (network geometry, types
and frequency of observations, and expected precisions of these
observations) to what will ultimately be measured in the field, the
better your resulting field work will match your design results.
In COLUMBUS, can I assign a global standard deviation to each observation type without having to change each observation standard deviation individually?
Yes! COLUMBUS was developed to simplify these types of what-if analyses.
Simply enter the OPTIONS - NETWORK OPTIONS - DEFAULT OBS SDs dialog box and set the standard deviation for all applicable observation types to a non-zero value. Changes only apply during network
design or adjustment. They do not change your data within the current project.
For azimuths, zeniths, bearings, directions and horizontal angles, the
units are gons or seconds. For all others, the units are the current
Look in Quick Tips for more information on Network Design.
Network Adjustment and Coordinate Transformation
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