Geography Reference
In-Depth Information
connected through the Internet network, to a reference GPS station, at which it is
subscribed and from which it can take the differential corrections. In relation to this, it is
mentioned that the National Romanian Service ROMPOS - DGNSS provides
corrections for the real time kinematic applications with a positioning accuracy
evaluated at the interval between 3.0 and 0.5 meters for the receiver with a single
frequency. The ROMPOS - RTK service delivers corrections for the real time kinematic
applications with a positioning accuracy value situated between 0.5 and 2.0 cm for the
receivers with two frequencies (Stoica, 2008);
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To increase the time marking accuracy of the obtained video images, the video cameras
triggering is achieved from exterior by the PPS signal (Pulse Per Second) received from
the GPS satellite system, which, also, contains in its message, besides of the positioning
data, the data regarding the Universal Time - UTC;
4.2. Tightly coupled GPS/INS
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In order to continuously maintain the achieved positioning precision, the GPS system is
tight coupled with an IMU (Inertial Measuring Unit) unit, the data of these systems
being distributed through a filtering element of Kalman type. By integrating GPS and
INS, the accurate GPS position is used to update the INS, and the latter then produces
the high rate of accurate position and attitude data of mobile mapping system. The INS
is needed for continuously measure the camera location and orientation. Combining
GPS, INS and Distance Measurement Indicator (DMI) data is a very efficient and
accurate method to determine the position (lat/long/height), azimuth, pitch and roll
angles of the system cameras. The measurements of the INS come from two sensor
triads, an accelerometer block and a gyro block. They are defined as three components
of the specific force vector and three components of the body rotation rate. Integrated
with GPS data, the system geometry data are calculated using the Kalman method.
(Moafipoor S. et al., 2004)
The integrated GPS/INS solution produces continuous, smooth position and orientation of
the system even when the GPS signals are lost due to obstructions such as bridges, trees,
tunnels, mountains, high-rise buildings or limited and sporadic satellite coverage.
Taking into account of the functioning details described here, the figure 13 presents the
complete set of devices which compose our Mobile Slide Monitor.
4.3. SPAN (Synchronized Position Attitude Navigation) technology:
Bidirectional INS/GPS coupling to obtain the objectives positioning with an
improved accuracy and continuity
Inertial Measuring Systems - INS are used on land, at sea and in the air as well as in space to
determine the dynamic properties and trajectory of a moving object. They are, also, used for
navigation, guidance and control or stabilisation of objects.
