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If you start a scenario that uses an NMEA file with more than 12000 epochs, GSG will ini-
tiate a dialog upon start of the scenario, asking you to either cancel the simulation exe-
cution, or to truncate the NMEA trajectory file down to its first 12000 epochs.
Making a One-Line Trajectory
As the GSG unit uses the heading and speed information of the RMC sentences, only one
(!) NMEA sentence is actually required to describe a simple, continuous movement.
For example, the following one-line trajectory specifies a continuous north bound tra-
jectory (as the heading field is set to 0.0 degrees) at a speed of 77 knots.
$GPRMC,111150,A,6000.0000,N,0100.0000,E,77.000,0.0,010101,0.9,W,A*03
One-line trajectories like this can be easily be made by manually creating desired NMEA
files. The example above can be taken as a baseline, then edit speed and/or heading fields
as required. For the validity of the sentence, the last 2 digits contain a checksum of the
data (XOR of all bytes between $ and * symbols) – this checksum must be correct and can
be
calculated with e.g., this online tool:
http://www.hhhh.org/wiml/proj/nmeaxor.html
. Note that the NMEA messages, includ-
ing the checksums, are case sensitive and should be given in UPPERCASE even if the GSG
unit (firmware version 3.00 and above) accepts messages in lower case.
3.5.5 Ephemeris
The satellite constellations and the transmitted navigation data of each satellite are dynam-
ically built, once you start the scenario or the signal generation. The constellation and the
navigation data is based on
RINEX data
stored in the unit, or uploaded to the unit. The con-
stellation orbits can be refined by providing precise orbit information in
SP3 format
(for
details, see below).
GPS and QZSS almanac data may optionally be provided in the form of YUMA files (for
details, see below).
In addition, SBAS message files are also supported (see "SBAS Satellites" on page 82 and
"User-Uploaded Ephemeris" on page 49 below for more details).
Under the menu item Select > Select Scenario > Configure > Ephemeris , there are two
or three options to choose from (as described below), in order to select a source for your
scenario navigation data:
Default
Download
User-uploaded files .
3.5 "Select" Menu
User Manual GSG-5/6 Series Rev. 27 47