R/coordinatesTransformations.R

In asteRisk: Computation of Satellite Position

calculatePolarMotionMatrix <- function(julianDate) {
    hasData()
    # Old code where polar coefficients xp and yp are calculated instead of 
    # retrieved from data, based on Grady Hillhouse C++ implementation of
    # Vallado's MatLab implementation
    # MJD <- julianDate - 2400000.5
    # A <- 2 * pi * (MJD - 57226) / 365.25
    # C <- 2 * pi * (MJD - 57226) / 435
    # xp <- (0.1033 + 0.0494*cos(A) + 0.0482*sin(A) + 0.0297*cos(C) + 0.0307*sin(C)) * 4.84813681e-6
    # yp <- (0.3498 + 0.0441*cos(A) - 0.0393*sin(A) + 0.0307*cos(C) - 0.0297*sin(C)) * 4.84813681e-6
    # polarMotionMatrix <- matrix(c(cos(xp), 0, -sin(xp),
    #                               sin(xp)*sin(yp), cos(yp), cos(xp)*sin(yp),
    #                               sin(xp)*cos(yp), -sin(yp), cos(xp)*cos(yp)),
    #                             nrow=3, ncol=3, byrow=TRUE)
    # New code using observed/predicted values retrieved from Celestrak, still
    # using 80's nutation theory
    MJD <- trunc(julianDate - 2400000.5)
    earthPositionsRow <- asteRiskData::earthPositions[asteRiskData::earthPositions[,4] == MJD, ]
    # Multiplication factor to convert from arcseconds to radians
    xp <- earthPositionsRow[5] * 4.84813681e-6
    yp <- earthPositionsRow[6] * 4.84813681e-6
    polarMotionMatrix <- matrix(c(cos(xp), 0, -sin(xp),
                                  sin(xp)*sin(yp), cos(yp), cos(xp)*sin(yp),
                                  sin(xp)*cos(yp), -sin(yp), cos(xp)*cos(yp)),
                                nrow=3, ncol=3, byrow=TRUE)
    return(polarMotionMatrix)
}

TEMEtoITRF <- function(position_TEME, velocity_TEME=c(0,0,0), dateTime) {
    gmst <- UTCdateTimeToGMST(dateTime)
    daysToJ2000_0 <- as.numeric(julian(as.POSIXct(dateTime, tz="UTC"),
                                       origin=as.POSIXct("2000-01-01 12:00:00", tz="UTC")))
    julianDate <- daysToJ2000_0 + JD_J2000_0
    MJD_UTC <- julianDate - 2400000.5
    MJD_trunc <- trunc(MJD_UTC)
    if(MJD_trunc > asteRiskData::earthPositions[nrow(asteRiskData::earthPositions), 4]) {
        stop(strwrap("Attempting conversion for a date for which Earth orientation
                     parameters are not currently available. Please run 
                     getLatestSpaceData() and try again. If the problem persists,
                     the date is too long into the future and not even predicted
                     parameters are available."), 
             initial="", prefix="\n")
    }
    MJD_TT <- MJDUTCtoMJDTT(MJD_UTC)
    T_TT <- (MJD_TT - MJD_J2000)/36525
    meanLongitudeAscendingNodeMoon <- (125.04452222 + T_TT * (-(5*360 + 134.1362608) + T_TT * (0.0020708 + T_TT * 2.2e-6))) * pi/180
    meanLongitudeAscendingNodeMoon <- meanLongitudeAscendingNodeMoon %% (2*pi)
    if(julianDate > 2450449.5) {
        gmst <- gmst + 
            (0.00264 * sin(meanLongitudeAscendingNodeMoon) + 0.000063 * sin(2 * meanLongitudeAscendingNodeMoon)) * pi/648000
    }
    PEF_TOD_matrix <- matrix(c(cos(gmst), -sin(gmst), 0,
                               sin(gmst), cos(gmst), 0,
                               0, 0, 1),
                             nrow=3, ncol=3, byrow=TRUE)
    position_PEF <- as.vector(t(PEF_TOD_matrix) %*% position_TEME)
    polarMotionMatrix <- calculatePolarMotionMatrix(julianDate)
    position_ECEF <- as.vector(t(polarMotionMatrix) %*% position_PEF)
    # Old version uses 0.002 as constant value for Length of Day (LOD)
    # omegaEarth <- c(0, 0, 7.29211514670698e-05 * (1.0  - 0.002/86400.0))
    # Now changed to get exact value from EOP tables
    LOD <- asteRiskData::earthPositions[asteRiskData::earthPositions[,4] == MJD_trunc, 8]
    omegaEarth <- c(0, 0, 7.29211514670698e-05 * (1.0  - LOD/86400.0))
    velocity_PEF <- as.vector(t(PEF_TOD_matrix) %*% velocity_TEME) -
        c(omegaEarth[2] * position_PEF[3] - omegaEarth[3] * position_PEF[2],
          omegaEarth[3] * position_PEF[1] - omegaEarth[1] * position_PEF[3],
          omegaEarth[1] * position_PEF[2] - omegaEarth[2] * position_PEF[1])
    velocity_ECEF <- as.vector(t(polarMotionMatrix) %*% velocity_PEF)
    return(list(
        position=position_ECEF,
        velocity=velocity_ECEF
    ))
}

ITRFtoLATLON <- function(position_ITRF, degreesOutput=TRUE) {
    a <- earthRadius_WGS84
    a2 <- a^2
    f <- earthFlatteningFactor_WGS84
    b <- a*(1-f)
    b2 <- b^2
    e <- sqrt((a2 - b2)/a2)
    eprime <- sqrt((a2 - b2)/b2)
    X <- position_ITRF[1]
    Y <- position_ITRF[2]
    Z <- position_ITRF[3]
    p <- sqrt(X^2 + Y^2)
    theta <- atan2(a*Z, b*p)
    sintheta <- sin(theta)
    costheta <- cos(theta)
    num <- Z + eprime^2 * b * sintheta^3
    denom <- p - e^2 * a * costheta^3
    lat <- atan2(num, denom)
    lon <- atan2(Y, X)
    N <- a/(sqrt(1 - e^2 * (sin(lat))^2))
    alt <- p / cos(lat) - N
    if(abs(lon) >= pi) {
        if(lon < 0) {
            lon <- lon + 2*pi
        } else {
            lon <- lon - 2*pi
        }
    }
    LATLONALT <- if(degreesOutput)  c(rad2deg(lat), rad2deg(lon), alt) else c(lat, lon, alt)
    names(LATLONALT) <- c("latitude", "longitude", "altitude")
    return(LATLONALT)
}

LATLONtoITRF <- function(position_LATLON, degreesInput=TRUE) {
    lat <- position_LATLON[1]
    lon <- position_LATLON[2]
    alt <- position_LATLON[3]
    if(degreesInput) {
        lat <- deg2rad(lat)
        lon <- deg2rad(lon)
    }
    # Prime-vertical radius of curvature
    N <- earthRadius_WGS84/(sqrt(1 - earthEccentricity_WGS84^2 * sin(lat)^2))
    position_ECEF <- c((N + alt) * cos(lat) * cos(lon),
                       (N + alt) * cos(lat) * sin(lon),
                       ((1 - earthEccentricity_WGS84^2) * N + alt) * sin(lat))
    return(unname(position_ECEF))
}

TEMEtoLATLON <- function(position_TEME, dateTime, degreesOutput=TRUE) {
    ECEFcoords <- TEMEtoITRF(position_TEME=position_TEME, dateTime=dateTime)
    return(ITRFtoLATLON(ECEFcoords$position, degreesOutput=degreesOutput))
}

ITRFtoGCRF <- function(position_ITRF, velocity_ITRF=c(0, 0, 0), dateTime) {
    hasData()
    date <- strptime(dateTime, format="%Y-%m-%d %H:%M:%S", tz = "UTC")
    year <- date$year + 1900
    month <- date$mon + 1
    day <- date$mday
    hour <- date$hour
    minute <- date$min
    second <- date$sec
    Mjd_UTC <- iauCal2jd(year, month, day, hour, minute, second)$DATE
    results <- ECEFtoECI(Mjd_UTC, c(position_ITRF, velocity_ITRF))
    return(list(
        position=as.numeric(results$position),
        velocity=as.numeric(results$velocity)
    ))
}

GCRFtoITRF <- function(position_GCRF, velocity_GCRF=c(0, 0, 0), dateTime) {
    hasData()
    date <- strptime(dateTime, format="%Y-%m-%d %H:%M:%S", tz = "UTC")
    year <- date$year + 1900
    month <- date$mon + 1
    day <- date$mday
    hour <- date$hour
    minute <- date$min
    second <- date$sec
    Mjd_UTC <- iauCal2jd(year, month, day, hour, minute, second)$DATE
    results <- ECItoECEF(Mjd_UTC, c(position_GCRF, velocity_GCRF))
    return(list(
        position=as.numeric(results$position),
        velocity=as.numeric(results$velocity)
    ))
}

TEMEtoGCRF <- function(position_TEME, velocity_TEME=c(0,0,0), dateTime) {
    hasData()
    ecef_results <- TEMEtoITRF(position_TEME, velocity_TEME, dateTime)
    GCRF_results <- ITRFtoGCRF(ecef_results$position, ecef_results$velocity, dateTime)
    return(GCRF_results)
}

GCRFtoLATLON <- function(position_GCRF, dateTime, degreesOutput=TRUE) {
    hasData()
    ECEFcoords <- GCRFtoITRF(position_GCRF=position_GCRF, dateTime=dateTime)
    return(ITRFtoLATLON(ECEFcoords$position, degreesOutput=degreesOutput))
}

LATLONtoGCRF <- function(position_LATLON, dateTime, degreesInput=TRUE) {
    hasData()
    ECEFcoords <- LATLONtoITRF(position_LATLON, degreesInput=degreesInput)
    return(ITRFtoGCRF(ECEFcoords, dateTime=dateTime))
}

KOEtoECI <- function(a, e, i, M, omega, OMEGA, keplerAccuracy=10e-8, maxKeplerIterations=100) {
    # calculate true anomaly from mean anomaly
    convergence <- FALSE
    iterations <- 0
    Eomega <- M
    while(!convergence) {
        iterations <- iterations + 1
        delta_kepler_sol <- - ( (Eomega - e*sin(Eomega) - M) / (1 - e*cos(Eomega)) )
        Eomega <- Eomega + delta_kepler_sol
        if(iterations > maxKeplerIterations | delta_kepler_sol < keplerAccuracy) {
            convergence <- TRUE
        }
    }
    nu <- 2 * atan2(sqrt(1 + e) * sin(Eomega/2), sqrt(1 - e) * cos(Eomega/2))
    R <- a * (1 - e*cos(Eomega))
    orbital_position <- R * c(cos(nu), sin(nu), 0)
    orbital_velocity <- (sqrt(GM_Earth_TDB * a)/R) * c(-sin(Eomega), sqrt(1-e^2) * cos(Eomega), 0)
    eci_position <- c(orbital_position[1] * (cos(omega) * cos(OMEGA) - sin(omega) * cos(i) * sin(OMEGA)) -
                          orbital_position[2] * (sin(omega) * cos(OMEGA) + cos(omega) * cos(i) * sin(OMEGA)),
                      orbital_position[1] * (cos(omega) * sin(OMEGA) + sin(omega) * cos(i) * cos(OMEGA)) +
                          orbital_position[2] * (cos(omega) * cos(i) * cos(OMEGA) - sin(omega) * sin(OMEGA)),
                      orbital_position[1] * sin(omega) * sin(i) + orbital_position[2] * cos(omega) * sin(i))
    eci_speed <- c(orbital_velocity[1] * (cos(omega) * cos(OMEGA) - sin(omega) * cos(i) * sin(OMEGA)) -
                       orbital_velocity[2] * (sin(omega) * cos(OMEGA) + cos(omega) * cos(i) * sin(OMEGA)),
                   orbital_velocity[1] * (cos(omega) * sin(OMEGA) + sin(omega) * cos(i) * cos(OMEGA)) +
                       orbital_velocity[2] * (cos(omega) * cos(i) * cos(OMEGA) - sin(omega) * sin(OMEGA)),
                   orbital_velocity[1] * sin(omega) * sin(i) + orbital_velocity[2] * cos(omega) * sin(i))
    return(list(
        position=eci_position,
        velocity=eci_speed
    ))
}


ECItoKOE <- function(position_ECI, velocity_ECI) {
    # calculate orbital momentum
    eps <- .Machine$double.eps
    h <- vectorCrossProduct3D(position_ECI, velocity_ECI)
    e_vector <- vectorCrossProduct3D(velocity_ECI, h)/GM_Earth_TDB - position_ECI/sqrt(sum(position_ECI^2))
    # This is equivalent to the following expression by Vallado 2007
    # e_vector2 <- ((sum(velocity_ECI^2) - GM_Earth_TDB/sqrt(sum(position_ECI^2)))*position_ECI - 
    # (position_ECI%*%velocity_ECI)*velocity_ECI )/GM_Earth_TDB
    e <- sqrt(sum(e_vector^2))
    node_vector <- c(-h[2], h[1], 0)
    E <- sum(velocity_ECI^2)/2 - GM_Earth_TDB/sqrt(sum(position_ECI^2))
    if(abs(E) > eps) {
        a <- -GM_Earth_TDB/(2*E)
        # p <- a*(1-e^2)
    } else {
        # p <- sum(h^2)/GM_Earth_TDB
        a <- Inf
    }
    # Vallado´s implementation defines p always as follows
    p <- sum(h^2)/GM_Earth_TDB
    i <- acos(h[3]/sqrt(sum(h^2)))
    # determine special orbit cases
    orbitType <- "ei" # general case: non-circular (elliptical) orbit with inclination
    if(e < eps) { # almost 0 eccentricity: circular orbits
        if(i < eps | abs(i - pi) < eps) { # no inclination: equatorial orbits
            orbitType <- "ce"
        } else {
            orbitType <- "ci" # circular inclined
        }
    } else if(i < eps | abs(i - pi) < eps) { # elliptical equatorial orbit
        orbitType <- "ee"
    }
    if(sqrt(sum(node_vector^2)) > eps) {
        cosOMEGA <- node_vector[1]/sqrt(sum(node_vector^2))
        if(abs(cosOMEGA) > 1) {
            cosOMEGA <- sign(cosOMEGA)
        }
        OMEGA <- acos(cosOMEGA)
        if(node_vector[2] < 0) {
            OMEGA <- 2*pi - OMEGA
        }
    } else {
        OMEGA <- NaN
    }
    if(orbitType == "ei") {
        omega <- acos((node_vector%*%e_vector)/(sqrt(sum(node_vector^2))*e))
        if(e_vector[3] < 0) {
            omega <- 2*pi - omega
        }
    } else {
        omega <- NaN
    }
    if(orbitType %in% c("ei", "ee")) {
        nu <- acos((e_vector%*%position_ECI)/(e*sqrt(sum(position_ECI^2))))
        if(position_ECI %*% velocity_ECI < 0) {
            nu <- 2*pi - nu
        }
    } else {
        nu <- NaN
    }
    # non-standard orbital parameters
    # argument of latitude - for non-equatorial orbits
    if(orbitType %in% c("ci", "ei")) {
        arglat <- acos((node_vector%*%position_ECI)/(sqrt(sum(node_vector^2))*sqrt(sum(position_ECI^2))))
        if(position_ECI[3] < 0) {
            arglat <- 2*pi - arglat
        }
    } else {
        arglat <- NaN
    }
    # longitude of perigee - elliptical equatorial orbits
    if(orbitType == "ee") {
        cosLonPer <- e_vector[1]/e
        if(abs(cosLonPer) > 1) {
            cosLonPer <- sign(cosLonPer)
        }
        lonPer <- acos(cosLonPer)
        if(e_vector[2] < 0) {
            lonPer <- 2*pi - lonPer
        }
        if(i > 0.5*pi) {
            lonPer <- 2*pi - lonPer
        }
    } else {
        lonPer <- NaN
    }
    # true longitude - circular equatorial orbits
    if((sqrt(sum(position_ECI^2)) > eps) & orbitType == "ce") {
        cosTrueLon <- position_ECI[1] / sqrt(sum(position_ECI))
        if(abs(cosTrueLon) > 1) {
            cosTrueLon <- sign(cosTrueLon)
        }
        trueLon <- acos(cosTrueLon)
        if(position_ECI[2] < 0) {
            trueLon <- 2*pi - trueLon
        }
        if(i > 0.5*pi) {
            trueLon <- 2*pi - trueLon
        }
    } else {
        trueLon <- NaN
    }
    # calculate mean anomaly for non-circular orbits
    if(orbitType %in% c("ei", "ee")) {
        if(e < 1 - eps) { 
            # truly elliptical orbit
            sine <- (sqrt(1-e^2)*sin(nu)) / (1 + e*cos(nu))
            cose <- (e + cos(nu)) / (1 + e*cos(nu))
            e0 <- atan2(sine, cose)
            m <- e0 - e*sin(e0)
        } else if((e > 1 + eps) & (abs(nu) + 1e-5 < pi - acos(1/e))) { 
            # hyperbolic orbit
            sine <- (sqrt(-1+e^2)*sin(nu)) / (1 + e*cos(nu))
            e0 <- asinh(sine)
            m <- e*sinh(e0) - e0
        } else if(abs(nu) < 168*pi/180) {
            # parabolic orbit
            e0 <- tan(nu/2)
            m <- e0 + e0^3/3
        }
        if(e < 1) {
            m <- rem(m, 2*pi)
            if(m < 0) {
                m <- m + 2*pi
            }
            e0 <- rem(e0, 2*pi)
        }
    } else {
        m <- NaN
    }
    return(list(
        semiMajorAxis = a,
        eccentricity = e,
        inclination = i,
        meanAnomaly = as.vector(m),
        argumentPerigee = as.vector(omega),
        longitudeAscendingNode = OMEGA,
        trueAnomaly = as.vector(nu),
        argumentLatitude = as.vector(arglat),
        longitudePerigee = lonPer,
        trueLongitude = trueLon
    ))
}

### New coordinate transformations with quaternion rotations

rotationMODtoGCRF <- function(MJD_UTC) {
    MJD_TT <- MJDUTCtoMJDTT(MJD_UTC)
    precession <- IAU76_precession(MJD_TT)
    rotation <- anglesToQuaternion(c(precession$z,
                                     -precession$theta,
                                     precession$zeta),
                                   "ZYZ")
    return(rotation)
}

rotationGCRFtoMOD <- function(MJD_UTC) {
    inverseRotation <- rotationMODtoGCRF(MJD_UTC)
    return(Conj(inverseRotation))
}

rotationTEMEtoMOD <- function(MJD_UTC, deltaDeltaPsi = 0, deltaDeltaEps = 0) {
    MJD_TT <- MJDUTCtoMJDTT(MJD_UTC)
    nutation <- IAU76_nutation(MJD_TT)
    nutation$deltaPsi <- nutation$deltaPsi + deltaDeltaPsi
    nutation$deltaEps <- nutation$deltaEps + deltaDeltaEps
    obliquity <-  nutation$meanEclipticObliquity + nutation$deltaEps
    T_TT <- (MJD_TT - MJD_J2000)/36525 # Julian centuries in TT
    meanLongitudeAscendingNodeMoon <- (125.04452222 + T_TT * (-(5*360 + 134.1362608) + T_TT * (0.0020708 + T_TT * 2.2e-6))) * pi/180
    meanLongitudeAscendingNodeMoon <- meanLongitudeAscendingNodeMoon %% (2*pi)
    equationEquinoxes1982 <- nutation$deltaPsi * cos(nutation$meanEclipticObliquity) +
        (0.00264 * sin(meanLongitudeAscendingNodeMoon) + 0.000063 * sin(2 * meanLongitudeAscendingNodeMoon)) * pi/648000
    quatTEMEtoTOD <- anglesToQuaternion(-equationEquinoxes1982, "Z")
    quatTODtoMOD <- anglesToQuaternion(c(obliquity, nutation$deltaPsi, -nutation$meanEclipticObliquity), "XZX")
    return(quatTEMEtoTOD * quatTODtoMOD)
}

rotationMODtoTEME <- function(MJD_UTC, deltaDeltaPsi = 0, deltaDeltaEps = 0) {
    inverseRotation <- rotationTEMEtoMOD(MJD_UTC, deltaDeltaPsi, deltaDeltaEps)
    return(Conj(inverseRotation))
}

rotationGCRFtoTEME <- function(MJD_UTC) {
    IERS_results <- IERS(asteRiskData::earthPositions, MJD_UTC, interp = "l")
    quatGCRFtoMOD <- rotationGCRFtoMOD(MJD_UTC)
    quatMODtoTEME <- rotationMODtoTEME(MJD_UTC, IERS_results$dpsi, IERS_results$deps)
    return(quatGCRFtoMOD * quatMODtoTEME)
}

rotationTEMEtoGCRF <- function(MJD_UTC) {
    inverseRotation <- rotationGCRFtoTEME(MJD_UTC)
    return(Conj(inverseRotation))
}

rotationPEFtoMOD <- function(MJD_UTC, deltaDeltaPsi = 0, deltaDeltaEps = 0) {
    MJD_TT <- MJDUTCtoMJDTT(MJD_UTC)
    MJD_UT1 <- MJDUTCtoMJDUT1(MJD_UTC)
    nutation <- IAU76_nutation(MJD_TT)
    nutation$deltaPsi <- nutation$deltaPsi + deltaDeltaPsi
    nutation$deltaEps <- nutation$deltaEps + deltaDeltaEps
    obliquity <-  nutation$meanEclipticObliquity + nutation$deltaEps
    T_TT <- (MJD_TT - MJD_J2000)/36525 # Julian centuries in TT
    meanLongitudeAscendingNodeMoon <- (125.04452222 + T_TT * (-(5*360 + 134.1362608) + T_TT * (0.0020708 + T_TT * 2.2e-6))) * pi/180
    meanLongitudeAscendingNodeMoon <- meanLongitudeAscendingNodeMoon %% (2*pi)
    equationEquinoxes1982 <- nutation$deltaPsi * cos(nutation$meanEclipticObliquity) +
        (0.00264 * sin(meanLongitudeAscendingNodeMoon) + 0.000063 * sin(2 * meanLongitudeAscendingNodeMoon)) * pi/648000
    thetaGMST <- MJDToGMST(MJD_UT1)
    thetaGAST <- thetaGMST + equationEquinoxes1982
    quatPEFtoTOD <- anglesToQuaternion(-thetaGAST, "Z")
    quatTODtoMOD <- anglesToQuaternion(c(obliquity, nutation$deltaPsi, -nutation$meanEclipticObliquity), "XZX")
    return(quatPEFtoTOD * quatTODtoMOD)
}

rotationMODtoPEF <- function(MJD_UTC, deltaDeltaPsi = 0, deltaDeltaEps = 0) {
    inverseRotation <- rotationPEFtoMOD(MJD_UTC, deltaDeltaPsi, deltaDeltaEps)
    return(Conj(inverseRotation))
}

rotationGCRFtoJ2000 <- function(MJD_UTC) {
    IERS_results <- IERS(asteRiskData::earthPositions, MJD_UTC, interp = "l")
    quatGCRFtoMOD <- rotationGCRFtoMOD(MJD_UTC)
    quatMODtoPEF <- rotationMODtoPEF(MJD_UTC, IERS_results$dpsi, IERS_results$deps)
    quatPEFtoMOD <- rotationPEFtoMOD(MJD_UTC, 0, 0)
    quatMODtoJ2000 <- rotationMODtoGCRF(MJD_UTC)
    return(quatGCRFtoMOD * quatMODtoPEF * quatPEFtoMOD * quatMODtoJ2000)
}

rotationJ2000toGCRF <- function(MJD_UTC) {
    inverseRotation <- rotationGCRFtoJ2000(MJD_UTC)
    return(Conj(inverseRotation))
}

rotationTODtoMOD <- function(MJD_UTC, deltaDeltaPsi = 0, deltaDeltaEps = 0) {
    MJD_TT <- MJDUTCtoMJDTT(MJD_UTC)
    nutation <- IAU76_nutation(MJD_TT)
    nutation$deltaPsi <- nutation$deltaPsi + deltaDeltaPsi
    nutation$deltaEps <- nutation$deltaEps + deltaDeltaEps
    obliquity <-  nutation$meanEclipticObliquity + nutation$deltaEps
    quatTODtoMOD <- anglesToQuaternion(c(obliquity, nutation$deltaPsi, -nutation$meanEclipticObliquity), "XZX")
}

rotationMODtoTOD <- function(MJD_UTC, deltaDeltaPsi = 0, deltaDeltaEps = 0) {
    inverseRotation <- rotationTODtoMOD(MJD_UTC, deltaDeltaPsi = 0, deltaDeltaEps = 0)
    return(Conj(inverseRotation))
}

rotationGCRFtoTOD <- function(MJD_UTC) {
    IERS_results <- IERS(asteRiskData::earthPositions, MJD_UTC, interp = "l")
    quatGCRFtoMOD <- rotationGCRFtoMOD(MJD_UTC)
    quatMODtoTOD <- rotationMODtoTOD(MJD_UTC, IERS_results$dpsi, IERS_results$deps)
    return(quatGCRFtoMOD * quatMODtoTOD)
}

rotationTODtoGCRF <- function(MJD_UTC) {
    inverseRotation <- rotationGCRFtoTOD(MJD_UTC)
    return(Conj(inverseRotation))
}

rotationJ2000toMOD <- function(MJD_UTC) {
    IERS_results <- IERS(asteRiskData::earthPositions, MJD_UTC, interp = "l")
    quatGCRFtoMOD <- rotationGCRFtoMOD(MJD_UTC)
    quatMODtoPEF <- rotationMODtoPEF(MJD_UTC, 0, 0)
    quatPEFtoMOD <- rotationPEFtoMOD(MJD_UTC, IERS_results$dpsi, IERS_results$deps)
    return(quatGCRFtoMOD * quatMODtoPEF * quatPEFtoMOD)
}

rotationMODtoJ2000 <- function(MJD_UTC) {
    inverseRotation <- rotationJ2000toMOD(MJD_UTC)
    return(Conj(inverseRotation))
}

### Future user-level functions for conversions based on quaternions and DCM

J2000toGCRF <- function(coordinates, dateTime) {
    MJD <- dateTimeToMJD(dateTime)
    DCM <- quaternionToDCM(rotationJ2000toGCRF(MJD))
    return(drop(
        DCM %*% coordinates
    ))
}

GCRFtoJ2000 <- function(coordinates, dateTime) {
    MJD <- dateTimeToMJD(dateTime)
    DCM <- quaternionToDCM(rotationGCRFtoJ2000(MJD))
    return(drop(
        DCM %*% coordinates
    ))
}

### Other frames: SEZ/ENU/NEZ

rotationITRFtoENU <- function(coordinatesITRF) {
    latlonalt <- ITRFtoLATLON(coordinatesITRF, degreesOutput = FALSE)
    lat <- latlonalt[1]
    lon <- latlonalt[2]
    DCM <- matrix(c(-sin(lon), cos(lon), 0,
                    -cos(lon)*sin(lat), -sin(lon)*sin(lat), cos(lat),
                    cos(lon)*cos(lat), sin(lon)*cos(lat), sin(lat)),
                  nrow=3, byrow = TRUE)
    return(DCM)
}

ITRFtoENU <- function(coordinates) {
    DCM <- rotationITRFtoENU(coordinates)
    return(drop(
        DCM %*% coordinates
    ))
}

calculateRazel <- function(geocentricObserver, geocentricSatellite, degreesOutput=TRUE) {
    rangeVector <- geocentricSatellite - geocentricObserver
    elevation <- acos(sum(geocentricObserver * rangeVector)/sqrt(sum(geocentricObserver^2)*sum(rangeVector^2)))
    elevation <- pi/2 - elevation
    azimuthCos <- (-geocentricObserver[3]*(sum(geocentricObserver[1:2]*rangeVector[1:2])) + sum(geocentricObserver[1:2]^2)*rangeVector[3])/
        sqrt(sum(geocentricObserver[1:2]^2)*sum(geocentricObserver^2)*sum(rangeVector^2))
    azimuthSin <- (-geocentricObserver[2]*rangeVector[1] + geocentricObserver[1]*rangeVector[2])/
        sqrt(sum(geocentricObserver[1:2]^2)*sum(rangeVector^2))
    azimuth <- atan2(azimuthSin, azimuthCos)
    range <- sqrt(sum(rangeVector^2))
    RAZEL <- if(degreesOutput)  c(rad2deg(azimuth), rad2deg(elevation), range) else c(azimuth, elevation, range)
    names(RAZEL) <- c("azimuth", "elevation", "range")
    return(RAZEL)
}