asteRisk (version 1.4.3)

LATLONtoGCRF: Convert coordinates from geodetic latitude, longitude and altitude to GCRF

Description

The GCRF (Geocentric Celestial Reference Frame) frame of reference is an Earth-centered inertial coordinate frame, where the origin is also placed at the center of mass of Earth and the coordinate frame is fixed with respect to the stars (and therefore not fixed with respect to the Earth surface in its rotation). The X-axis is aligned with the mean equinox of Earth at 12:00 Terrestrial Time on the 1st of January, 2000, and the Z-axis is aligned with the Earth´s rotation axis. This function converts geodetic latitude, longitude and altitude to Cartesian coordinates in the GCRF frame. The WGS84 Earth ellipsoid model is used.

Usage

LATLONtoGCRF(position_LATLON, dateTime, degreesInput=TRUE)

Value

A vector with three elements, corresponding to the X, Y and Z components of position in meters in the ECEF frame, in this order.

Arguments

position_LATLON

Vector with the latitude, longitude and altitude of the object. Latitude and longitude can be provided in sexagesimal degrees or in radians (by default, sexagesimal degrees are asumed). Altitude must be provided in meters.

dateTime

Date-time string with the date and time in UTC corresponding to the provided geodetic coordinates.

degreesInput

Logical indicating if the input latitude and longitude are in sexagesimal degrees. If degreesInput=FALSE, the input will be considered to be in radians. This specifies the time for which the conversion from geodetic coordinates to GCRF will be performed. It is important to provide an accurate value, since the point over the surface of Earth to which a set of GCRF coordinates corresponds varies with time due to the motion of Earth.

References

https://apps.dtic.mil/sti/pdfs/ADA280358.pdf

Examples

if(requireNamespace("asteRiskData", quietly = TRUE)) {
latitude <- 37.3891
longitude <- -5.9845
altitude <- 20000

# Let´s calculate the corresponding coordinates in GCRF frame, assuming that
# the provided coordinates were valid the 20th of October, 2020 at 15:00:00 UTC

coordinatesGCRF <- LATLONtoGCRF(c(latitude, longitude, altitude), 
                                dateTime="2020-10-20 15:00:00")
}