d. Stop-and-go kinematic surveying involves 1 to 2 minutes of data collection at each station (after
a period of initialization) to gain the integers. This technique does not allow for loss of lock during the
survey. If loss of lock does occur, a new period of initialization must take place. This method should be
performed with two fixed or known stations to provide redundancy and improve accuracy.
e. Pseudokinematic surveying is similar to standard kinematic and static procedures combined.
The differences are that there is no static initialization and there is a longer period of data collection at
each station (1 to 5 minutes). Each point must be revisited after one hour, and the loss of lock is
acceptable. Pseudokinematic surveying is less acceptable for establishing baselines because the
positional accuracy is less than for kinematic or rapid-static surveying.
f. OTF/RTK kinematic surveying uses GPS technology to allow positioning to less than a
decimeter in real time. This system determines the integer number of carrier wavelengths from the GPS
antenna to the GPS satellite, transmitting them while in motion and without static initialization. The
basic concept behind the OTF/RTK kinematic system is kinematic surveying without static initialization
(integer initialization is performed while moving) and allowances for loss of lock. Other GPS
techniques which can achieve this kind of accuracy require static initialization while the user is not
moving and does not allow for loss of lock while in motion.
5-24. The Impact of the Global Positioning System. The impact of GPS on geodetic-control surveys
has been immense. In the past, surveyors relied upon line-of-sight instrumentation to develop
coordinates. With GPS, ground station intervisibility is no longer required, and much longer lines can
be surveyed. Different instruments and survey techniques were previously used to measure horizontal
and vertical coordinates, leading to two different networks with little overlap. GPS, on the other hand, is
a 3D system.
5-25. Vertical Measurements with GPS. GPS is not recommended for third-order or higher vertical-
control surveys. It is not recommended as a substitute for standard differential leveling, but rather for
small-scale topographic mapping or similar projects. The height component of GPS measurements is
the weakest plane because the orbital geometry of the X-Y-Z position determination. Thus, GPS-
ellipsoidal height differences are usually less accurate than the horizontal components. GPS-derived
elevation differences do not meet third-order standards as those obtained using conventional levels.
Accordingly, GPS-derived elevations must be used with caution.
5-26. GPS Height Determinations. GPS positioning, whether operated in an absolute or differential
positioning mode, can provide heights (or height differences) of surveyed points. The height or height
difference obtained from GPS is in terms of height above or below the WGS-84 ellipsoid. The ellipsoid
heights are not the same as orthometric heights or elevations, which are obtained from conventional
differential leveling. This distinction between ellipsoid heights and orthometric elevations is critical to
many engineering and construction projects. GPS users must
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EN0593
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