RINEX (Receiver Independent Exchange Format) is one of the most widely used formats for providing data of satellite navigation systems. The RINEX standard defines several file types, among which navigation files are used to distribute positional information of the satellites. The exact information provided in a RINEX navigation file varies for each satellite navigation system. This function reads RINEX navigation files for satellites of the GPS constellation, operated by the USA.
readGPSNavigationRINEX(filename)Path to the GPS RINEX navigation file.
A list with two elements. The first element, named header, is a list with
the following elements:
Version of the RINEX format used in the file
Type of RINEX file
Program used to generate the RINEX file
Individual or organization that generated the file
Date-time string indicating when the file was created
Coefficient for ionospheric correction A0
Coefficient for ionospheric correction A1
Coefficient for ionospheric correction A2
Coefficient for ionospheric correction A3
Coefficient for ionospheric correction B0
Coefficient for ionospheric correction B1
Coefficient for ionospheric correction B2
Coefficient for ionospheric correction B3
A0 parameter to compute accurate time in UTC
A1 parameter to compute accurate time in UTC
Time in seconds of current UTC week for reference time
UTC reference week number
Leap seconds introduced since 1980. Useful to convert to UTC time (UTC time = GPS time - leap seconds)
Miscellaneous comments found in the header of the RINEX file
The second element is named messages, and it contains one element for each navigation message found in the RINEX file. Each of these elements is a list with the following elements that provide information about the position of the GPS satellite:
PRN code of the satellite. Unique PRN codes are assigned to all satellites in global navigation satellite systems, and therefore provide an identifier for each of them
Epoch year in 2-digit format. If lower than 80, the meaning should be taken as 20XX, while if larger than 80, it refers to 19XX.
Epoch month
Epoch day
Epoch hour
Epoch minute
Epoch second
Date-time string indicating the time corresponding to the reported position in the present message. The time is in UTC, obtained by subtracting the leap seconds (if available in the header) from the time of the satellite system (which is in GPS time). If leap seconds are not provided in the header, the time will be in GPS. For an even more accurate conversion to actual UTC time, the clock bias, clock drift and possibly even clock drift rate (described in the next three elements) must be considered
Clock bias (i.e., constant offset) that should be applied to the satellite time in order to obtain an even more accurate UTC time. In seconds
Clock drift of the satellite clock that should be applied in combination with the time difference to the reference time in order to obtain an even more accurate UTC time. In seconds per second
Rate of change for the clock drift of the satellite clock. It is frequently 0, but if not, it should be applied in combination with clock bias and clock drift in order to obtain an even more accurate UTC time. In seconds per square second.
Issue-of-data ephemeris. It acts as a time-stamp or unique identifier for the provided navigation data. In particular, the IODE of a given navigation message should never be the same as the IODE for any other navigation message broadcasted by the same satellite in the past 6 days, although violations of this rule have been observed. Most frequently, IODE are not reused in a period of 7 days, so that they match exactly the IODC.
Amplitude of the sine harmonic component for the correction of orbital radius. In meters
Mean motion difference from computed value. In radians per second In order to obtain the real (perturbed) mean motion, first the Keplerian mean motion should be calculated from the semi-major axis. Then, deltaN should be added to it.
Mean anomaly of the satellite at epoch. In radians. This indicates where the satellite is along its orbital path. It is provided as the angle between the direction of the perigee and the hypothetical point where the object would be if it was moving in a circular orbit with the same period as its true orbit after the same amount of time since it last crossed the perigee had ellapsed. Therefore, 0 denotes that the object is at the perigee. This is a Keplerian orbital element.
Amplitude of the cosine harmonic component for the correction of latitude argument. In radians
Eccentricity of the orbit of the satellite at epoch. This is a Keplerian orbital element.
Amplitude of the sine harmonic component for the correction of latitude argument. In radians
Semi-major axis of the orbit of the satellite at epoch. In meters. This is a Keplerian orbital element
Time of the GPS week (in seconds) for the ephemeris
Amplitude of the cosine harmonic component for the correction of inclination. In radians
Longitude of the ascending node of the satellite at epoch, also known as right ascension of the ascending node, in radians. This is the angle between the direction of the ascending node (the point where the satellite crosses the equatorial plane moving north) and the direction of the First Point of Aries (which indicates the location of the vernal equinox). This is a Keplerian orbital element.
Amplitude of the sine harmonic component for the correction of inclination. In radians
Mean orbital inclination of the satellite in radians. This is the angle between the orbital plane of the satellite and the equatorial plane. This is a Keplerian orbital element.
Amplitude of the cosine harmonic component for the correction of orbital radius. In meters.
Mean argument of the perigee of the object in radians. This is the angle between the direction of the ascending node and the direction of the perigee (the point of the orbit at which the object is closest to the Earth). This is a Keplerian orbital element.
Angular velocity of the satellite with respect to the vernal equinox. In radians/second.
Flag indicating if coarse/acquisition (C/A) code is being transmitted on the L2 channel (value of 1) or not (value of 0)
GPS week number at epoch
Flag indicating if precise (P) code is being transmitted on the L2 channel (value of 1) or not (value of 0)
Accuracy of the position of the satellite, in meters.
Code indicating the health of the satellite. 0 if healthy.
Bias difference between codes broadcasted on L1 and the ionospheric-free combination of the codes broadcasted at L1 and L2, in seconds. This parameter, also known as timing group delay (TGD), should be considered when calculating satellite clock error.
Issue-of-data clock. It acts as a time-stamp or unique identifier for the provided navigation data. In particular, the IODC of a given navigation message should never be the same as the IODC for any other navigation message broadcasted by the same satellite in the past 7 days, although violations of this rule have been observed. Most frequently, IODE are not reused in a period of 7 days instead of the mandatory 6 days, so that they match exactly the IODC.
Transmission time for the navigation message, in seconds of GPS week.
Flag indicating for how long the broadcasted ephemeris are valid since the last time the data was updated. It should be noted that in order to obtain positional values/orbital elements at times other than epoch, the corrections for perturbed orbital elements should be applied and propagated. If 0, the ephemeris data are valid for up to 4 hours. If 1, they are valid for more than 4 hours.
https://gage.upc.edu/gFD/ https://www.navcen.uscg.gov/pubs/gps/rinex/rinex.txt ftp://www.ngs.noaa.gov/cors/RINEX211.txt http://acc.igs.org/misc/rinex304.pdf https://www.icao.int/Meetings/AMC/MA/2004/GNSS/icd.pdf
# NOT RUN {
# The file testGPSRINEX.txt provided with the package includes 3 navigation
# messages from 3 GPS satellites
testGPSnav <- readGPSNavigationRINEX(paste0(path.package("asteRisk"),
"/testGPSRINEX.txt"))
testGPSnav$header
testGPSnav$messages
# }
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