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3. SETTING AND ADJUSTMENT
3-34
Notes:
• Talker identifier can be separately defined for speed and course (VTG message) and for
position (GLL, GGA or PAT message). If talker identifier is defined as XX, then it is
ignored.
• IEC 61162-1 ed1 or ed2: GGA uses messages VTG and GGA. Recommended for DGPS.
Correct operation of a DGPS sensor requires that the system also receives VTG
message. If no VTG message is received, the system thinks that there is something
wrong in the DGPS and it downgrades the DGPS to an ordinary GPS sensor.
• IEC 61162-1 ed1: PAT uses messages VTG, PAT and SHR, POS. Alternative for a DGPS
which also gives pitch and roll data.
• IEC 61162-1 ed1: GLL uses messages VTG and GLL. Recommended for non differential
position receivers.
• IEC 61162-1 ed2: GLL uses messages VTG and GLL. Recommended for both differential
and non-differential position receivers.
• IEC 61162-1 ed1: GLL Use of differential signal with GPS can be detected with GGA and
SHR, POS. A device using identification GLL and device type 8 (= DGPS) will always be
detected as differential regardless of receiver status.
• COG delay is the delay between own ship turning and course made good in the VTG
message to detect turning. Typically values are from 0 to 15 seconds.
• Because no message has any datum indication, the user is responsible for reference
system used in the position receiver. GGA message is supposed to always be in WGS-84,
but unfortunately some manufacturers do not follow this standard.
• Only one of connected sensors is allowed to send ZDA message, which will be used to
adjust the system clock. If time difference is larger than 5 seconds and if the system is not
a part of steering (i.e., mode is not Goto Wp, Goto Track or Program Track Turn) and if
the system has Kalman filter in OFF position.
• Offset from antenna position to Conning position is essential for speed, course, drift and
predictor related calculation.
• Roll & pitch data may be enabled only with PAT.
• First two channels can also operate as general purpose outputs. Checksum related
parameters are for outputs only. Sent messages are GLL, VTG and HDT.
(NOTE: Output operation requires an SIF module instead on RIF module in the A adapter.
• There are two alternatives for IEC 61162-1 based interface: ed1 and ed2. Ed1 was
published and Ed2 was published in July 2000. The differences are new datum message
(DTM) and changed content of GLL position message.
• Ed2 requires that position information (in this case GLL or GGA messages) also contain
separate indication of datum used (DTM message). IMO rule state that the radar can only
accept position in WGS84 datum. In practice only EPFS (for example, GPS or DGPS),
which has "IEC 61162-1 Ed 2 (2000-7)" indicated in their type approval certificate can
detect Datum.
• Ed2 requires that the GLL message includes a quality indicator i.e., the GLL message can
indicate if position is based on standard GPS or differential GPS.