Spectracom GSG-5 series, Руководство пользователя с руководством по SCPI

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NMEA time-stamp. All other timestamps in the NMEA trajectory will be transformed accord
ingly, thus keeping the relative position/times in the NMEA trajectory intact.
A given NMEA trajectory can be replayed in any GPS time frame, utilizing any earth coordin
ates by specifying the desired start time and start position in the scenario.
Looping trajectories
The NMEA trajectory files can be configured either to be executed once, or to loop repeatedly
throughout the scenario execution. For the looping to be allowed, the NMEA trajectory has to
be continuous, meaning the first and last specified coordinates of the trajectory must be
identical (see also: "Duration" on page 39).
RMC vs. GGA
GSG-5/6 Series GNSS Simulators accept NMEA streams containing any set of valid NMEA
sentences, yet only information from RMC and/or GGA sentences will be used to build the tra
jectory (for detailed information on GGA and RMC, purchase the NMEA 0183 through
nmea.org
, or see e.g.,
here
). Either RMC messages, or GGA messages are accepted, or a
combination of both. The latter is preferable. All other types of sentences are ignored without
user notification.
All NMEA sentences – i.e. all characters between the start marker (‘$’) and the checksum (‘*’
plus two hex digits) – are validated for correct syntax. The only accepted error is an incorrect
checksum (because incorrect checksums can be useful for manually correcting the contents of an
NMEA file).
Date, time, position, speed, heading
Date and time along with longitude, latitude, speed over ground, and heading will be extrac
ted from the RMC message (NMEA’s Recommended Minimum), in order to build the trajectory.
Altitude
RMC messages do not include altitude data, hence if no GGA messages are available, the start
position altitude specified in scenario parameters will be used instead.
Heading and speed over ground specified in the NMEA file will be applied only to the last
epoch of the trajectory, since all other points they will be computed by two adjacent positions.
This technique prevents the undesirable behavior of some receivers which generate NMEA data
using heading and speed data that does no correspond to position change.
Heading and speed changes
GNSS receivers are generally very sensitive to g-forces, and unrealistic movements will result in
the receiver losing track of the simulated signals. Therefore, trajectories should at all times
describe smooth, realistic movements, i.e. using gradual transitions in acceleration and head
ing, rather than abrupt commands (such as random user-set coordinates or speed changes).
Any parts of a trajectory describing changes in heading and/or speed must be provided in 10
Hz increments.
3.5 "Select" Menu
CHAPTER
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User Manual GSG-5/6 Series Rev. 26
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