Appendix 3.  Description of Data Exchange Formats

Two formats (FICA and RINEX) have been used to distribute GPS phase and pseudorange data from single tracking sessions, and a third (ARGOS) used by NGS to distribute week-long data from CIGNET stations prior to 1992.  In addition, each of these formats has a file or blocks defined to contain ephemeris and clock information broadcast by the satellites  Finally, orbital ephemerides in tabular (XYZ per epoch) format are distributed in the SP1 or SP3 ("Standard Product") format developed by NGS and now used by the IGS.  The ARGOS format is described in Chapter 9 (section 9.2); the others are described below.

A.3.1  RINEX

The Receiver INdependent EXchange format for GPS data provides the current IGS standard for the distribution of phase and pseudorange data ("o" file) and the navigation message ("n") file recorded by a receiver.  There is also a less used file for meteorological data.  Version 1 of the RINEX formats is described in ["A Common Exchange Format for GPS Data by Gurtner, W., G. Mader, and D. MacArthur, in Proceedings of the Fifth International Geodetic Symposium on Satellite Systems, Las Cruces, New Mexico, 1989] and reprinted in CIGNET Bulletin 2 (3), May–June, 1989.  Version 2 is described in CIGNET Bulletin 3 (3), September–October, 1990.  A sample of a Version 1 RINEX navigation file is given in the section A.3.3.

A 3.2  FICA

TI4100 data prior to 1989 were usually distributed in the Floating-Integer-Character-ASII (FICA) format devised by the Applied Research Laboratory at the University of Texas.  A description of the format and definitions of the standard TI 4100 blocks and (ad hoc) MIT-defined blocks used to create an acceptable input file for MAKEX from NGS ARGO format, see the comments in subroutines blknnn.f in gamit/makex. 

A.3.3 Description of the E-file

The E-file consists of one or more "blocks" of Broadcast Ephemeris data as recorded by the receiver from the satellites' transmissions.  For convenience we have not introduced a new format for these data; rather, they may be either in RINEX navigation file format (preferred) or in FICA format as defined by GESAR Block 9 for the TI 4100.  To create an E-file for from a TI FICA file, use the program FICACHOP and specify Block 9.  

An example of a RINEX navigation file, with an ephemeris block for only one satellite, is given below:

     1              NAVIGATION DATA                         RINEX VERSION / TYPE
 MAKEX v. 7.1 of 90/07/09 apollo   king  1990-07-06 19:16:30 PGM / RUN BY / DATE

 8 88 11  8  4  8  59.1	0.323700718582E-03	0.171894498635E-09	-0.277555756156E-16
	0.102400000000E+05	0.104687500000E+02	0.177400246575E-08	-0.199337541371E+01
	0.603497028351E-06	0.530868989881E-02	0.652857124805E-05	0.515373352242E+04
	0.194400000000E+06	-0.856816768646E-07	0.108490472307E+01	0.186264514923E-07
	0.110755363248E+01	0.330250000000E+03	-0.584334212505E+00	-0.634633577893E-08
	0.274297139863E-09	0.100000000000E+01	0.461000000000E+03	0.000000000000E+00
	0.700000000000E+01	0.600000000000E+02	0.000000000000E+00	0.102400000000E+05

The first line is a header giving the RINEX version number (1) and the type of file (the "N" in column 21 is the critical character).  The second line is a comment describing how the file was created.  Additional comment lines can be added by putting "COMMENT" in columns 61-67.  A blank line separates the header from the data blocks.  

The first line of each data block has the PRN number (8 here), epoch in GPST, and the three satellite clock polynomial coefficients (see Section  4.6).  The next 24 describe the ephemeris of the satellite.  Their definition and use is given, e. g., in King et al., Chapter 7.  The correspondences are listed in Table A.3.1 below.

An example of one block of a FICA-type E-file is given below.  The first line indicates that there are 60 floating point numbers in the block (and no integers or character strings).  

BLK      9   60    0    0
 	0.0000000000000E+00 	0.0000000000000E+00 	0.0000000000000E+00	0.0000000000000E+00
 	0.0000000000000E+00	 3.8500000000000E+02 	0.0000000000000E+00	0.0000000000000E+00
 	0.0000000000000E+00 	0.0000000000000E+00 	0.0000000000000E+00	0.0000000000000E+00
 	0.0000000000000E+00 	0.0000000000000E+00 	0.0000000000000E+00	0.0000000000000E+00
 	0.0000000000000E+00 	0.0000000000000E+00 	0.0000000000000E+00	1.3000000000000E+01
 	0.0000000000000E+00 	0.0000000000000E+00 	0.0000000000000E+00	0.0000000000000E+00
 	0.0000000000000E+00 	0.0000000000000E+00 	2.6250000000000E+00	2.0854440099709E-09
	-2.4993916368254E+00 	1.8067657947540E-07 	2.7529464568943E-03	 6.5285712480545E-06
 	5.1537107257843E+03 	1.1520000000000E+05 	0.0000000000000E+00	0.0000000000000E+00
 	0.0000000000000E+00 	0.0000000000000E+00 	0.0000000000000E+00	0.0000000000000E+00
 	0.0000000000000E+00 	0.0000000000000E+00 	0.0000000000000E+00	0.0000000000000E+00
 	0.0000000000000E+00	-5.5879354476929E-08	-2.0695827239133E+00 	1.0058283805847E-07
 	1.0937269895249E+00 	3.2003125000000E+02	-4.2112338394786E-01	-6.4691980394937E-09
 	0.0000000000000E+00 	2.1822337559381E-10 	0.0000000000000E+00	0.0000000000000E+00
 	0.0000000000000E+00 	0.0000000000000E+00 	0.0000000000000E+00	0.0000000000000E+00

For the most part, the numbers in the FICA Blk 9 are the same as those used in the RINEX-type E-file but in a different order.  

Table A.3.1   Broadcast ephemeris values in RINEX and FICA E-files

			RINEX file	FICA Blk 9
Description	Line #, Index	Index No.

	Clock drift rate  ( sec/sec2 )	SV Clk   3	14
	Clock drift   (sec/sec )	SV Clk   2	15
	Clock bias  (sec)	SV Clk   1	16
	Age of ephemeris data  (GPS sec of week)	Orb 1   1	26
	Radial sine correction  (CRS)  (meters)	Orb 1   2	27
	Correction to mean motion  (radians/sec)	Orb 1   3	28
	Mean anomaly at epoch  (radians)	Orb 1   4	29
	In-track cosine amplitude  (CUC)  (radians)	Orb 2   1	30
	Eccentricity	Orb 2   2	31
	In-track sine amplitude  (CUS)   (radians) 	Orb 2   3	32
	Square root of the semi-major axis   ( meter1/2 )	Orb 2   4	33
	Time of epoch  (GPS seconds of week)	Orb 3   1	34
	Inclination cosine correction  (CIC)  (radians)	Orb 3   2	46
	Right ascension of ascending node  (radians)	Orb 3   3	47
	Inclination sine correction  (CIS)  (radians)	Orb 3   4	48
	Inclination  (radians)	Orb 4   1	49
	Radial cosine adjustment  (radians)	Orb 4   2	50
	Argument of perigee  (radians)	Orb 4   3	51
	Rate of change of right ascension of ascending node  (rad/s)	Orb 4   4	52
	Rate of change of inclination  (radians/sec)	Orb 5   1	54
	Codes on L2 channel	Orb 5   2
	Full week number  (GPS weeks)	Orb 5   3	6
	L2 P data flag	Orb 5   4
	SV accuracy	Orb 6   1	8
	SV health	Orb 6   2	9
	Receiver channel		19
	Satellite PRN number		20
	Clock epoch  (GPS sec of week)		13
	HOW word  (GPS seconds of week)		3
	Age of ephemeris data  (GPS sec of week)		53

A 3.2  SP3 Orbit File

A complete description of the NGS standard GPS orbit products is given by Remondi [NOAA Tech. Rep. NOS 133 NGS 46, 1989].  The one most commonly used and adopted by the IGS for distribution of earth-fixed ephemerides is SP#3; an example for the official IGS orbit is shown below:

#aP1996  4 21  0  0   .00000000      96 ORBIT ITR93 HLM  IGS
##  850       .00000000   900.00000000 50194  .0000000000000
+   25     1  2  3  4  5  6  7  9 14 15 16 17 19 20 21 22 23
+         24 25 26 27 28 29 31 18  0  0  0  0  0  0  0  0  0
+          0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
+          0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
+          0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
++         5  5  6  5  5  5  5  5  5  5  8  5  6  5  5  5  5
++         5  5  5  6  5  5  5  8  0  0  0  0  0  0  0  0  0
++         0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
++         0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
++         0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
%c cc cc ccc ccc cccc cccc cccc cccc ccccc ccccc ccccc ccccc
%c cc cc ccc ccc cccc cccc cccc cccc ccccc ccccc ccccc ccccc
%f   .0000000   .000000000   .00000000000   .000000000000000
%f   .0000000   .000000000   .00000000000   .000000000000000
%i    0    0    0    0      0      0      0      0         0
%i    0    0    0    0      0      0      0      0         0
/* RAPID SERVICE ORBIT COMBINATION FROM WEIGHTED AVERAGE OF:
/* cod emr esa gfz jpl ngs sio                              
/* REFERENCED TO GPS CLOCK AND TO WEIGHTED MEAN POLE:       
/*                                                          
*  1996  4 21  0  0   .0000    
P  1 -20844.049743  16468.077022    682.661913     53.575584
P  2  12944.844539 -10393.087331 -20299.519500   -249.520521
P  3  -8227.617128  20375.326181 -15102.650518      4.597767
P  4  13744.791940  -9683.391414  20694.419314     22.047268
P  5 -12352.621960 -20060.938827  12297.360719     36.113385
P  6 -19546.655943  -1100.613728  18148.758754      8.140737
P  7  20712.125279 -16356.600000   -518.876248    719.138221
P  9 -17764.134276 -16037.093050 -11757.505817    -18.951339
P 14  12179.034086  18588.450559  14478.113351     13.465001
P 15  19057.231547  15809.204514  -9780.269336    293.252400
P 16  -1083.799746 -26408.146377   2349.366780      8.084014
P 17 -24486.194361  -4762.735719  -9703.838269   -112.969182
P 19  25533.173686   3886.160764  -6400.473223    459.005144
P 20 -15478.615183  -9745.065423  19106.255998     14.598467
P 21 -12024.261423  12964.155803 -19620.557712    -19.797230
P 22  -3194.548377  24157.840245  10016.934756    301.593609
P 23 -15229.612960  -1727.102967 -21438.845352      9.526407
P 24    544.423674 -15500.071774  21780.182095   -179.844909
P 25 -11610.793056  11908.640383  20691.294205     -1.623070
P 26  -3511.667947 -15876.253008 -20761.862582   -183.285168
P 27  21532.343236  -3952.280131 -15530.087869     26.271555
P 28 -12532.981692  20254.408891 -11879.931632     78.225844
P 29  12432.222182   9589.973773  21587.240169      8.991759
P 31   4170.173983  15571.909204 -21199.804060    447.486131
P 18  21074.399097  -2889.491428  15694.503544 999999.999999
*  1996  4 21  0 15   .0000    
P  1 -20941.140297  16195.390001  -2157.407872     53.634533
 ...

The characters in columns 1 and 2 indicate the type of line.  The first line (#a) includes the GPST date and time (year, month, day, hour, minute, second) of the start of the orbital information, the number of epochs (96 in the example), the terrestrial coordinate system used (ITR93, for ITRF-93) and the agency computing the the orbit (IGS).  The keyword in columns 41–45 indicates the type of data used to compute the orbit.  For individual analysis centers this will indicate.e.g. doubly differenced carrrier phase ( d ), but for the IGS combined orbit the orbits of the individual analysis centers are the "observations".  The second line (##) repeats the start time but in terms of GPS week (850) plus seconds of week and Modified Julian Day plus fraction-of-day; it also gives the interval of the tabulated ephemerides in seconds (900).  

The third to the seventh lines (+ ) have the number of satellites followed by their respective PRN numbers.  The 8th to the 12th lines (++) indicate the accuracy of the orbit of each satellite, given by the exponent of 2 in millimeters; e.g., 5 implies an accuracy of 25 mm, or 3.2 cm.   Lines 13–18 are reserved for addition of character (%c), floating-point (%f) or integer (%i) variables to the format.  Lines 19–22 have free-form comments (/*).

For each epoch there is a header line (* ) and data lines (P ) for each satellite.  The data lines contain Cartesian coordinates in kilometers andthe clock offset in microseconds.