44. I downloaded one of the precise orbit files (igr13600.sp3.z) from the NGS website and was wondering at the format of the data. The SP3 format link states that the data is either position or velocity, which is indicated by either a "P" or a "V" at the beginning of each line, followed by 4 values. This file has a "PG" at the beginning of each line. I assume that this is position. However, there are 4 integers after the clock bias (or drift for velocity) term. What are these numbers? I was also wondering what the units are when the data is velocity. The SP3 format link gives the units for position data only.
A. You are looking at the new format which we (NGS) label "sp3c" for the time being. This orbit file will include glonass satellites. The P represents position, the G represents GPS satellite and R for glonass. Eventually, like the IGS, this "sp3c" will be the new "sp3" file.
Here is a line from an "sp3c" file showing "base" numbers...
%f 1.2500000 1.025000000 0.00000000000 0.000000000000000
If we had a program to convert sp3c to add velocity then the epoch showing velocity would look like ....
Check out ....
http://igscb.jpl.nasa.gov/igscb/data/format/sp3c.txt for a description of the "new" sp3 ( sp3c ) format.
1.25 is the base number for sdevs of X, Y, and Z
1.025 is the base number for sdev of the clock offset
kilometers from earth center of mass microsecs (base**n mm)
base is 1.25(base**n picosecs)
base is 1.025
Position GPS PRN1 X Y Z PRN clock offset X sdev
nY sdev
nZ sdev
nclock sdev
n
PG01 -17277.867518 -15136.238599 13567.996481 44.522498 5 8 8 149
Velocity (dm/sec) microsecs/sec (base**n * 10**-04 mm/sec)
base is 1.25(base**n* 10**-04 picosecs/sec)
base is 1.025
Velocity GPS PRN1 X Y Z PRN clock offset X sdev
n
Y sdev
nZ sdev
nclock sdev
n
VG01 20298.880364 -18462.044804 1381.387685 -4.534317
14 14 14 191