File Format ID: r2rnav

Format Description Creation Date: 2011-03-15
Last Revised: 2013-05-07

File Type: ASCII, tab-separated values

Record Format: 

Data Format Description:
Introduction:

We define three R2R navigation standard products to be produced from each cruise: 
NavBestRes, Nav1Min, and NavControl. These three products specify the ship's
time-stamped positions. The first three columns of each product contain (1) a 
single string for date and time, (2) longitude, and (3) latitude. The NavBestRes 
product is a quality-controlled product based on the ship's best GPS antenna
position files provided in the ship's data distribution. It includes additional
columns: (4) GPS quality indicator (defined by NMEA-0183), (5) number of GPS 
satellites, (6) horizontal dilution of precision, and (7) the GPS antenna height 
above/below mean sea level [meters]. "BestRes" refers to the fact that this 
product represents the highest resolution in time and allows for differences 
among vessels (or among legacy data) in the time interval used for recording the 
ship's position. Common practice among vessels is to collect position data at 
the maximum rate capable of today's marine GPS receivers: once-per-second. Times
are specified at one-minute intervals in the Nav1Min product. The NavControl 
product is a subset of the Nav1Min product, just enough points to draw a 
ship-track on a map.

Columns 8 and 9 of the NavBestRes product contain instantaneous 
speed-over-ground and course-over-ground, respectively.  The instantaneous 
speed-over-ground has units of m/s, and is computed from single-differences
of successive positions (from the current position to the next position).  
Course and speed are computed on the WGS-84 reference ellipsoid using 
Vincenty's formula.  The course-over-ground is measured in degrees clockwise 
from north.

Similarly, columns 4 and 5 of the Nav1Min product contain the same 
instantaneous speed-over-ground and course-over-ground as given for the 
identical record in the NavBestRes product.  In other words, these are
preserved from the NavBestRes product and not recomputed using 
once-per-minute positions.

Date and time:

The ISO8601 time standard defines the order of date and time to be year, 
month, day, hour, minute, second, followed by a time-zone identifier. 
Section 6.2.3 of RFC5424 goes a step farther and specifies the characters 
used to separate these quantities and requires the inclusion of fractions 
of second, if known. We adopt these standards and add the additional 
requirement that UTC time be used in all R2R navigation standard products.

An example date and time specified in this format is:

2009-08-27T13:30:00.000Z

The year is specified with four digits. The month, day, hour, minute, and 
integer number of seconds are specified with two digits. The number of 
digits to the right of the decimal place depends on the precision reported 
in fractions of a second. The day refers to day of month. The 24-hour clock 
is used to specify the hour. The hyphen ("-") is used between year and 
month, and between month and day. The capital letter "T" is used between 
date and time. The colon (":") is used between hour and minute, and between 
minute and second. The trailing capital letter "Z" specifies UTC time. No 
whitespace is allowed in this date and time format.

Ship's Position:

The ship's position is specified in units of decimal degrees, longitude
followed by latitude. The bounds for longitude and latitude are as 
follows: -180 <= lon < 180 and -90 <= lat <= 90. We reproduce the GPS 
receiver precision. For example, if the longitude is recorded in the ship's
data distribution to the nearest 0.0001 arc-minute, the longitude in the 
standard product will be reported to the nearest 0.000001 degrees (= 0.0001 
arc-minute * 1/60 degree-per-arc-minute). The datum in common use by marine 
GPS receivers is WGS84.

NMEA-0183 definition of GPS quality indicator:

The National Marine Electronics Association has defined the following values 
for the GPS quality indicator:

0 = fix not available or invalid
1 = GPS Standard Positioning Service (SPS) mode, fix valid
2 = differential GPS, SPS mode, fix valid
3 = GPS Precise Positioning Service (PPS) mode, fix valid
4 = Real Time Kinematic (RTK). Satellite system used in RTK mode with fixed 
integers
5 = Float RTK. Satellite system used in RTK mode with floating integers
6 = Estimated (dead reckoning) mode
7 = Manual input mode
8 = Simulator mode

Flagging of bad positions in NavBestRes format:

Here, a bad position is defined as a position that results in a physically 
unreasonable horizontal acceleration (for a ship, approx. greater than 
1 m/s^2), a record with a poor GPS quality indicator (an invalid fix or 
an estimate based on dead reckoning), fewer than 4 satellites, or a record 
containing a duplicate or earlier date/time.  It must also be remembered 
that the GPS horizontal position uncertainty for marine antennas is 
typically no better than 1 meter.  A record containing a bad position will 
be flagged with a leading pound "#" sign.

(Bad positions will not be included in the Nav1Min and NavControl standard 
products and so flagging is unnecessary.)

Header records:

Each of the three products contains a three-line header.  Each header line
is prefixed by two forward slashes "//".  The first header record is a
tab-delimited list of column names with units of measure (if any).  The
second header record is the URI to this document.  The third header record
is the creation date of the file.

File naming convention:

The file naming convention is to use cruise ID, underscore ("_"), lowercase 
"bestres", "1min", or "control", followed by the filename extension 
".r2rnav" (all lowercase). An example for a cruise on the R/V Roger Revelle 
with a cruise ID of RR1103 is:

NavBestRes product: RR1103_bestres.r2rnav
Nav1Min product: RR1103_1min.r2rnav
NavControl product: RR1103_control.r2rnav

Example Content:
NavBestRes:

2011-02-26T08:22:14.00Z	121.995782	25.162922	2	8	2.3	26	5.95	120.187
2011-02-26T08:22:15.00Z	121.995833	25.162895	2	8	2.3	26	6.09	120.611
2011-02-26T08:22:16.00Z	121.995885	25.162867	2	8	2.3	26	5.87	124.479
2011-02-26T08:22:17.00Z	121.995933	25.162837	2	8	2.3	26	5.67	131.653
2011-02-26T08:22:18.00Z	121.995975	25.162803	2	8	2.3	26	5.74	132.479

Nav1Min:

2011-02-26T08:22:14.00Z	121.995782	25.162922	5.95	120.187
2011-02-26T08:23:00.00Z	121.997828	25.161395	5.74	132.478
2011-02-26T08:24:00.00Z	122.000193	25.159007	5.92	138.415
2011-02-26T08:25:00.00Z	122.002507	25.156533	5.99	142.693
2011-02-26T08:26:00.00Z	122.004700	25.153957	5.79	139.906

NavControl:

2011-02-26T08:22:14.00Z	121.995782	25.162922
2011-02-26T08:40:00.00Z	122.042957	25.123002
2011-02-26T09:00:00.00Z	122.117362	25.110655
2011-02-26T10:49:00.00Z	122.146143	24.841670
2011-02-26T11:19:00.00Z	122.198682	24.765478

References: www.rvdata.us

