Spectra Precision Survey Pro v5.3 - Manual (Page 72)

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7. Leveling
Introduction What Leveling Is
Leveling is a surveying method that allows the most accurate measurement of
vertical distances between points. Using a starting point with know elevation,
the leveling survey method allows you to transfer the elevation to new points
by measuring vertical distance differences between the know elevation and the
position of the level instrument.
Leveling data collection is organized into level loops. A level loop is a sequence
of measurements that starts and ends on a point of know elevation. Many level
loops start and end on the same point, hence the name “loop”. However, you
can start and end a level loop on different points, provided the elevation is
known for both points.
NOTE: Collecting and storing points in a level loop is different than optical or GNSS
surveying in that for leveling, you often need to take many measurements before you
reach the point of interest in the survey where you want to store a new elevation.
The procedure for leveling with Survey Pro is almost the same no matter which
leveling method you are using. The main difference for each method is the type
of information that is collected with each shot taken.
You should have now selected a leveling method and possibly connected an
instrument to Survey Pro (if you are using an electronic level or an electronic
total station for trig leveling). See Leveling Mode - Getting Ready for Leveling
on page 32 for more information.
It’s a good idea, in the current job, to create the point from which your first
level loop will start. This point, which must have an accurate elevation, can
also be created when creating the level loop.
Other Definitions
• A level loop is a series of level measurements that start with a backsight
measurement on a known point with a valid elevation. This point is referred
to as the opening Control Benchmark (or opening CBM). The elevation of
the opening CBM will NOT be modified by the elevation measurements you
will collect in the loop.
A level loop is closed by taking a measurement to a point with a valid
elevation. This point is referred to as the closing Control Benchmark (or
closing CBM). Often, the closing CBM is the same point as the one where
you started the level loop, but it can also be any known point with an
accurate elevation.