readGPSNavigationRINEX {asteRisk}

Read a RINEX navigation file for GPS satellites

Description

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 structured text file types 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.

Usage

readGPSNavigationRINEX(filename)

Arguments

filename

Path to the GPS RINEX navigation file.

Value

A list with two elements. The first element, named header, is a list with the following elements:

rinexVersion

Version of the RINEX format used in the file

rinexFileType

Type of RINEX file

generatorProgram

Program used to generate the RINEX file

generatorEntity

Individual or organization that generated the file

fileCreationDateString

Date-time string indicating when the file was created

ionAlphaA0

Coefficient for ionospheric correction A0

ionAlphaA1

Coefficient for ionospheric correction A1

ionAlphaA2

Coefficient for ionospheric correction A2

ionAlphaA3

Coefficient for ionospheric correction A3

ionBetaB0

Coefficient for ionospheric correction B0

ionBetaB1

Coefficient for ionospheric correction B1

ionBetaB2

Coefficient for ionospheric correction B2

ionBetaB3

Coefficient for ionospheric correction B3

deltaUTCA0

A0 parameter, corresponding to bias between GPST and UTC time at the reference time (Tot) given by fields referenceTimeUTC and referenceWeekUTC. Should be used to compute accurate time in UTC

deltaUTCA1

A1 parameter, corresponding to the clock drift between GPST and UTC at the reference time (Tot) given by fields referenceTimeUTC and referenceWeekUTC. Should be used to compute accurate time in UTC

referenceTimeUTC

Time in seconds of current UTC week of Tot, which is the reference time to correct GPST time to UTC

referenceWeekUTC

UTC reference week number (continuous scale, not modulo 1024) of Tot.

leapSeconds

Leap seconds introduced since the 6th of January, 1980. Useful to convert to UTC time (UTC time = GPS time - leap seconds)

comments

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:

satellitePRNCode

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

tocYearShort

Toc 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. Toc is the GPS time of the specific satellite that should be used as the time reference to apply clock bias, clock drift and possibly even clock drift rate, as well as a relativistic correction, as described in the GPS system specification (https://www.gps.gov/technical/icwg/IS-GPS-200H.pdf) to obtain the corrected GPST system time. The GPST system time can be converted to UTC time by subtracting leap seconds since the 6th of January 1980 and performing another polynomial correction to account for bias and drift between GPST and UTC times.

tocMonth

Toc month

tocDay

Toc day

tocHour

Toc hour

tocMinute

Toc minute

tocSecond

Toc second

UTCepochDateTime

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

clockBias

Clock bias (i.e., constant offset) at Toc that should be applied to the satellite time in order to calculate accurate GPST. In seconds. Often referred to as af0.

clockDrift

Clock drift of the satellite clock at Toc that should be applied to the satellite time in order to calculate accurate GPST. In seconds. Often referred to as af1.

clockDriftRate

Rate of change for the clock drift of the satellite clock at Toc. It is frequently 0, but if not, it should be applied in combination with clock bias and clock drift in order to correct to GPST as accurately as possible. In seconds per square second. Often referred to as af2.

IODE

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.

radiusCorrectionSine

Amplitude of the sine harmonic component for the correction of orbital radius. In meters

deltaN

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.

correctedMeanMotion

Corrected mean motion calculated by adding deltaN to the value computed from the semi-major axis. In radians per second

meanAnomaly

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.

latitudeCorrectionCosine

Amplitude of the cosine harmonic component for the correction of latitude argument. In radians

eccentricity

Eccentricity of the orbit of the satellite at epoch. This is a Keplerian orbital element.

latitudeCorrectionSine

Amplitude of the sine harmonic component for the correction of latitude argument. In radians

semiMajorAxis

Semi-major axis of the orbit of the satellite at epoch. In meters. This is a Keplerian orbital element

toeSecondsOfGPSWeek

Time of the GPS week (in seconds) for the ephemeris. Together with the toeGPSWeek, it can be used to calculate the ephemeris time in GPS time of the specific satellite, to which sequential corrections first to GPST and then to UTC should be applied.

inclinationCorrectionCosine

Amplitude of the cosine harmonic component for the correction of inclination. In radians

ascension

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.

inclinationCorrectionSine

Amplitude of the sine harmonic component for the correction of inclination. In radians

inclination

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.

radiusCorrectionCosine

Amplitude of the cosine harmonic component for the correction of orbital radius. In meters.

perigeeArgument

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.

OMEGADot

Angular velocity of the satellite with respect to the vernal equinox. In radians/second.

codesL2Channel

Flag indicating if coarse/acquisition (C/A) code is being transmitted on the L2 channel (value of 1) or not (value of 0)

toeGPSWeek

GPS week number at epoch

dataFlagL2P

Flag indicating if precise (P) code is being transmitted on the L2 channel (value of 1) or not (value of 0)

satelliteAccuracy

Accuracy of the position of the satellite, in meters.

satelliteHealthCode

Code indicating the health of the satellite. 0 if healthy.

totalGroupDelay

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.

IODC

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.

transmissionTime

Transmission time for the navigation message, in seconds of GPS week.

fitInterval

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.

ephemerisUTCTime

A nanotime object indicating the time corresponding to the reported position (ephemeris) in the present message. The time is in UTC, obtained by first applying the individual clock bias, clock drift and clock drift rate of the particular satellite (fields clockBias, clockDrift and clockDriftRate of each message) and a relativistic correction to obtain corrected GPST time (system-wide GPS time), and then subtraction of leap seconds since the 6th of January 1980 and a second polynomial correction (with fields deltaUTCA0 and deltaUTCA1 from the header) to obtain UTC time. Corrections are performed as described in the GPS system specifications (https://www.gps.gov/technical/icwg/IS-GPS-200H.pdf).

position_ITRF

Position of the satellite in the ITRF frame, calculated from the provided orbital ephemeris following the procedure described in the GPS system specifications. In meters.

velocity_ITRF

Velocity of the satellite in the ITRF frame, calculated from the provided orbital ephemeris following the procedure described in the GPS system specifications. In meters/second.

acceleration_ITRF

Acceleration of the satellite in the ITRF frame, calculated from the provided orbital ephemeris following the procedure described in the GPS system specifications. In meters/squared second.

References

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 https://www.gps.gov/technical/icwg/IS-GPS-200H.pdf

Examples

# 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