sp3c.txt

包含三个M文件

     Columns 2-4         Vehicle Id.        G01                 A1,I2.2
     Columns 5-18        x-velocity(dm/s)   __20298.880364      F14.6
     Columns 19-32       y-velocity(dm/s)   _-18462.044804      F14.6
     Columns 33-46       z-velocity(dm/s)   ___1381.387685      F14.6
     Columns 47-60       clock rate-chg     _____-4.534317      F14.6
     Column  61          Unused             _                   blank
     Columns 62-63       xvel-sdev          14                  I2
                         (b**n 10**-4 mm/sec)
     Column  64          Unused             _                   blank
     Columns 65-66       yvel-sdev          14                  I2
                         (b**n 10**-4 mm/sec)
     Column  67          Unused             _                   blank
     Columns 68-69       zvel-sdev          14                  I2
                         (b**n 10**-4 mm/sec)
     Column  70          Unused             _                   blank
     Columns 71-73       clkrate-sdev       191                 I3
                         (b**n 10**-4 psec/sec)
     Columns 74-80       Unused             _______             7 blanks



If the user wishes to include correlation information between the velocity
components and the clock correction rate-of-change, then a separate Velocity
and Clock Rate-of-Change Correlation Record can be added after each Velocity
and Clock Rate-of-Change Record.  This record gives the standard deviations
for the X-, Y-, Z-velocities and the clock correction rate-of-change with
greater resolution than the approximate values given in the Velocity and
Clock Rate-of-Change Record.


       SP3 Line Twenty seven - The Velocity and Clock Rate-of-Change Correlation
  Record (See example 2)

     Columns 1-2         Symbols            EV                  A2
     Columns 3-4         Unused             __                  2 blanks
     Columns 5-8         xvel-sdev          __22                I4
                         (10**-4 mm/sec)
     Column  9           Unused             _                   blank
     Columns 10-13       yvel-sdev          __22                I4
                         (10**-4 mm/sec)
     Column  14          Unused             _                   blank
     Columns 15-18       zvel-sdev          __22                I4
                         (10**-4 mm/sec)
     Column  19          Unused             _                   blank
     Columns 20-26       clkrate-sdev       ____111             I7
                         (10**-4 psec/sec)
     Column  27          Unused             _                   blank
     Columns 28-35       xy-correlation     _1234567            I8
     Column  36          Unused             _                   blank
     Columns 37-44       xz-correlation     _1234567            I8
     Column  45          Unused             _                   blank
     Columns 46-53       xc-correlation     _1234567            I8
     Column  54          Unused             _                   blank
     Columns 55-62       yz-correlation     _1234567            I8
     Column  63          Unused             _                   blank
     Columns 64-71       yc-correlation     _1234567            I8
     Column  72          Unused             _                   blank
     Columns 73-80       zc-correlation     _1234567            I8





If no Velocity and Clock Rate-of-Change Records or Correlation Records are
present, the last line in the file can be computed as follows:

     SP3 Line 22+NUMEPS*(NUMSATS+1)+1  (i.e., The Last Line)

     Columns 1-3         End of File        EOF                 A3



Discussion of the SP3-c Format

     On line one, character two is the format version identification
character.  This third SP3 version has been designated version 'c'. 
Subsequent versions will use lower case letters in alphabetical order.  The
first line comprises the Gregorian date and time of day of the first epoch
of the orbit, the number of epochs in the ephemeris file (up to 10 million),
the data used descriptor, the coordinate system used descriptor, the orbit
type descriptor, and the agency descriptor.  The data used descriptor was
included for ease in distinguishing between multiple orbital solutions from
a single organization.  This will have primary use for the agency generating
the orbit.  A possible convention is given below; this is not considered
final and suggestions are welcome.

     u   -- undifferenced carrier phase
     du  -- change in u with time
     s   -- 2-receiver/1-satellite carrier phase
     ds  -- change on s with time
     d   -- 2-receiver/2-satellite carrier phase
     dd  -- change in d with time
     U   -- undifferenced code phase
     dU  -- change in U with time
     S   -- 2-receiver/1-satellite code phase
     dS  -- change in S with time
     D   -- 2-receiver/2-satellite code phase
     dD  -- change in D with time
      +  -- type separator

     Combinations such as "__u+U" seem reasonable.  If the measurements used
were complex combinations of standard types, then one could use "mixed"
where mixed could be explained on the comment lines.  In examples 1 and 2,
the file is a combination of orbits from several agencies and so the data
used is designated as 'ORBIT'.

     Orbit type is described by a three character descriptor.  At this time
only four have been defined: FIT (fitted), EXT (extrapolated or predicted),
BCT (broadcast), and HLM (fitted after applying a Helmert transformation). 
Naturally, others are possible.  The computing agency descriptor allows four
characters (e.g. _NGS, _IGS, etc.).

     The second line has:  the GPS week; the seconds of the GPS Week elapsed
at the start of the orbit (0.0 <= seconds of week < 604800.0); the epoch
interval (0.0 < epoch interval < 100000.0) in seconds; the modified Julian
Day Start (where 44244 represents GPS zero time -- January 6, 1980); and
fractional part of the day (0.0 <= fractional < 1.0) at the start of the
orbit.

     The third line to the seventh lines indicate the number of satellites
followed by their respective identifiers.  The identifiers must use
consecutive slots and continue on lines 4-7, if required.  The value 0
should only appear after all the identifiers are listed.  Satellite
identifiers may be listed in any order.  However, for ease in reviewing
satellites included in the orbit file it is recommended that
alphabetical/numerical order be used.  Each identifier will consist of a
letter followed by a 2-digit integer between 01 and 99.  For example, "Gnn"
for GPS satellites, "Rnn" for GLONASS satellites, "Lnn" for Low-Earth
Orbiting (LEO) satellites, and "Enn" for Galileo satellites.  Other letters
will be allowed for other types of satellites.  Lower numbered satellites
must always have a preceding zero (e.g., "G09" not "G 9").  The letter,
which represents the Satellite System Indicator, must always be present
(i.e.," 09" is no longer a valid satellite identifier).  This is a
significant change from SP3-a and needs to be noted when software is updated
to read the new SP3-c format.  A list of identifiers created for LEO
satellites can be viewed at http://cddis.gsfc.nasa.gov/sp3c_satlist.html .

     The eighth line to the twelfth lines have the orbit accuracy exponents. 
The value 0 is interpreted as accuracy unknown.  A satellite's accuracy
exponent appears in the same slot on lines 8-12 as the identifier on lines
3-7.  The accuracy is computed from the exponent as in the following
example.  If the accuracy exponent is 13, the accuracy is 2**13 mm or ~ 8 m. 
The quoted orbital error should represent one standard deviation and be
based on the orbital error in the entire file for the respective satellite. 
This may lead to some distortion when orbit files are joined together, or
when a file contains both observed and predicted data.

     On the thirteenth line, columns 4-5 hold the File Type descriptor. 
This is a single character left-justified in the two-character field.  The
currently defined values are: "G " for GPS only files, "M " for mixed files, 
"R " for GLONASS only files, "L " for LEO only files, and "E " for Galileo
only files. No default values are implied; either "G ", "M ", "R ", "L ", or
"E " is required.  On this same line, columns 10-12 hold the Time System
Indicator.  In order to remove any ambiguity with respect to which time
system is being used in mixed files, this field specifies the time system
used in each SP3-c file: use "GPS" to identify GPS Time, "GLO" to identify
the GLONASS UTC time system, "GAL" to identify Galileo system time, "TAI"
to identify International Atomic Time, or "UTC" to identify Coordinated
Universal Time.  No default value is implied; either "GPS", "GLO", "GAL",
"TAI, or "UTC" must be specified.

     On Line fifteen, columns 4-13 hold the floating-point base number used
for computing the standard deviations for the components of the satellite
position and velocity.  Instead of using 2**nn as is done in lines 8-12 in
the header, better resolution can be attained using a number like 1.25**nn.
The units for position and velocity are mm and 10**-4 mm/sec, respectively. 
Likewise, columns 15-26 hold the floating-point base number for computing
the standard deviations for the clock correction and the rate-of-change of
the clock correction.  Again, instead of using 2**nnn, one might use a
number like 1.025**nnn.  The units for the clock correction and the rate-of-
change of the clock correction are picosec and 10**-4 picosec/sec,
respectively.

     Lines 13-18 have been designed so that additional parameters may be
added to the SP3 format.

     Lines 19-22 are free form comments (comments go in columns 4-60).

     Line 23 is the Epoch Header Record, showing the epoch date and time.

     Line 24 is the Position and Clock Record; the first character is always
'P'.  The positional values are in kilometers and are precise to 1 mm.  A
precision of 0.5 mm can be accommodated if rounding is used, i.e., the value
shown is never more than 0.5 mm from the computed value.  The clock values
are in microseconds and are precise to 1 picosecond. Bad or absent
positional values are to be set to 0.000000.  Bad or absent clock values are
to be set to _999999.999999.  The six integer nines are required, whereas
the fractional part nines are optional.  Columns 62-69 hold the two digit
exponents which represent the standard deviations of the satellite
coordinates in units of millimeters.  For example, if the base floating
point number from line fifteen is 1.25, and the two-digit exponent for the
X-coordinate is 18, then the standard deviation of the X-coordinate is
1.25**18 = 55.5112 or approximately 56 mm.  In a similar manner, columns 71-
73 hold a three-digit exponent representing the standard deviation for the
clock correction in units of picoseconds. As an example, if the base
floating point number from line fifteen is 1.025, and the three-digit
exponent for the clock correction is 219, then the standard deviation of the
clock correction is 1.025**219 = 223.1138 or approximately 223 picoseconds.
An exponent value of 99 or 999 would mean that a standard deviation was too
large to represent.  If a standard deviation is unknown, its field is left
blank.  Column 75 is the Clock Event Flag (either 'E' or blank).  An 'E'
flag is used to denote a discontinuity in the satellite clock correction
(this might be caused by a clock swap on the satellite).  The discontinuity
is understood to have occurred sometime between the previous epoch and
current epoch, or at the current epoch. A blank means either no event
occurred, or it is unknown whether any event occurred.  Column 76 is the
Clock Correction Prediction Flag (either 'P' or blank).  A 'P' flag
indicates that the satellite clock correction at this epoch is predicted.
A blank means that the clock correction is observed.   Column 79 is the
orbit Maneuver Flag (either 'M' or blank).  An 'M' flag indicates that
sometime between the previous epoch and the current epoch, or at the current
epoch, an orbit maneuver took place for this satellite.  As an example, if a
certain maneuver lasted 50 minutes (a satellite changing orbital planes)
then these M-flags could conceivably appear at five separate 15-minute orbit
epochs.  If the maneuver started at 11h 14m and lasted to 12h 04m, M-flags
would appear for the epochs 11:15, 11:30, 11:45, 12:00 and 12:15.  A
maneuver is loosely defined as any planned or humanly-detectable thruster
firing that changes the orbit of a satellite.  A blank means either no
maneuver occurred, or it is unknown whether any maneuver occurred.  Column
80 is the Orbit Prediction Flag (either 'P' or blank).  A 'P' flag indicates
that the satellite position at this epoch is predicted.  A blank means that
the satellite position is observed.  Since not all of the fields in columns
61 through 80 will be used at every epoch, not every Position and Clock
Record will be required to contain 80 columns; missing columns should be
interpreted as blanks.  Any program reading an SP3-c file must be prepared
to deal with short records (either by padding with blanks, or by some other
method). 

     Line 25 (in example 2) is the optional Position and Clock Correlation
Record.  This record type always begins with the characters 'EP'.  Columns
5-18 give the standard deviations for the X,Y,Z satellite coordinates in
units of mm.  The standard deviations in this record are given to greater
resolution than the approximate values given in the Position and Clock
Record. A value of 9999 would mean that a standard deviation was too large
to be represented. If a standard deviation is unknown, its field is left
blank.  Columns 20-26 give the standard deviation of the clock correction in
units of picoseconds.  A value of 9999999 would mean that the standard
deviation was too large to be represented.  Columns 28-80 are used to store
the correlation coefficients for xy, xz, xc, yz, yc, and zc.  Each 8-digit
integer would be divided by 10,000,000 to produce a correlation coefficient
between -0.9999999 and +0.9999999.  If some of the correlation coefficients
are omitted, a Position and Clock Correlation Record may contain less than
80 columns. 

     Line 26 (in example 2) is the optional Velocity and Clock Rate-of-