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### Navigation Data Processing on SIO R/V Melville ###
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Description by S.M.Smith, SIO/GDC, January 1995
DATA LOGGING:
-------------
As of January 1995, the primary navigation source is a GPS Trimble
Mod. 4000AX receiver which logs fixes at 3 to 5 second intervals into
log file 'GPTinpf' by program 'gps_log' (see 'GPTinpf.file.description').
GPS fixes are also logged from a Trimble Model 10X receiver, located on
the bridge and monitored by the ship's officers, into file '10Xinpf' at
3 to 5 second intervals by program 'DO10X' (see
'10Xinpf.file.description'); and from an Ashtech XII receiver at one
second intervals by program 'DOash' (see 'ASHinpf.file.description').
[A more accurate P-Code receiver is scheduled for installation in
mid-1995].
Navigation is also stored in several other forms: File 'CS_SPinpf' has
INS (Integrated Navigation System) records at 1 second intervals
containing: time: position (switchable sources, currently interpolated
from the Trimble 4000AX GPS fixes); heading from the ship's gyro; speed
from the Edo 2-D Doppler speed log; and sea surface temperature (see
'CS_SPinpf.file.description'). Once per hour a record in the same
format is written to file 'INS_onehour'. Another file, 'DR1hour'
contains hourly time, position, course and speed in a different format
(see 'DR1hour.file.description'). Unlike the other 'inpf' files which
contain data for only one day, the INS_onehour and DR1hour files
contain records cumulative from the beginning of the leg.
NEAR REALTIME DISPLAY (on mlvl61):
---------------------------------
Position is displayed on a near-realtime Mercator projection plot on a
Calcomp Mod 965 beltbed plotter with a plotting area of approximately
32"x30". Plot bounds, scale and track annotation are set from the
'xdock' window on the u/w watch terminal.
Position from the Primary GPS receiver and from the CS_SPinpf file is
also displayed in the "Lab-Display' window on the u/w watch terminal
and is updated at approximately 1 minute intervals.
Other position displays (executed at the Unix prompt):
buttn - lists present time, date, position, cse and spd.
when - calculates time and cse to go from position 1 to
position 2 or from present position to another;
also from present position to selected ports
try: "when fremantle".
where - calculates position for specified time in last 24 hrs.
(execute with no options to get usage)
DATA PROCESSING (on mlvl62):
---------------------------
The GPTinpf.[date] file is input to program 'gps2satdata' which smooths
the GPS data by applying a 2nd order Gaussian filter with a width of
approximately 3 minutes to the 3 to 5 second interval fixes and
outputs positions at 1 minute intervals into file 'satdata.[date]'
(see 'satdata.file.description').
The satdata.[date] file is then concatenated with the previous satdata
files into a cumulative file, satdata.[CRUISE]. This file is input to
program 'satdata_to_navbin' which writes a binary file, 'navbin.[CRUISE]'
and a log file flagging excessive speeds or speed changes between
fixes. This list, along with a track plot, is used to spot navigation
problems, which can be corrected by editing the satdata file and rerunning
the sat_to_navbin program. The corrected navbin.[CRUISE] file is then
merged by program 'uwmerg' with magnetics, depth and gravity into a binary
file, 'uwmrg.[CRUISE]' (See 'uw_merge.description').
The navbin.[CRUISE] file is also used, along with file 'SBraw.[date]',
as input to program 'swath_merge' to write a SeaBeam 2000 bathymetry
file,'SBmrg.{date]' merged with navigation. Likewise, the
navbin.[CRUISE] file is input, along with file 'SSraw.[DATE], to the
same swath_merge program to write a SeaBeam 2000 (4bit grayscale)
sidescan data file 'SSmrg.[DATE]'.
#end
Creation Date: 6 April 1995
SMS