asteRisk (version 1.4.3)

calculateRazel: Calculates azimuth, elevation and range of a given object

Description

The horizontal coordinate system, also called azimuth-elevation system, uses the local horizon of an observer as its fundamental plane. In it, a given point is defined by 2 main angles: azimuth and elevation. Azimuth defines the angle of the point around the horizon in the X-Y plane, measured from the true North and usually increasing towards the East. Elevation is the angle between the object and the X-Y plane. Finally, the range defines the distance between the observer and the point.

This function calculates the azimuth, elevation and range given the coordinates of an observed satellite and of an observer. Both sets of coordinates must be provided as Cartesian geocentric coordinates in ITRF.

Usage

calculateRazel(geocentricObserver, geocentricSatellite, degreesOutput=TRUE)

Value

A vector with three elements, corresponding to the azimuth and elevation in degrees (or radians if specified) and the range in the same unit as the provided Cartesian coordinates.

Arguments

geocentricObserver

Vector with the X, Y and Z components of the position of the observer in ITRF frame.

geocentricSatellite

Vector with the X, Y and Z components of the position of the satellite in ITRF frame.

degreesOutput

Logical indicating if the output should be in sexagesimal degrees. If degreesOutput=FALSE, the output will be in radians.

References

https://gssc.esa.int/navipedia/index.php/Transformations_between_ECEF_and_ENU_coordinates

Examples

# The following were the coordinates of Italsat-2 in ITRF the 27th of June, 2006
# at 00:58:29.34 UTC, in meters.

italsat_ITRF <- c(-37325542.8, 19152438.3, 138384.5)

# Let us calculate its azimuth, elevation and range for an observer from Tokyo.
# The latitude and longitude of the city are 35.6762 degrees North, 139.6503 
# degrees East. Let's assume an observer placed at sea level (0 m)
# We first convert these coordinates to ITRF:

observer_ITRF <- LATLONtoITRF(c(35.6762, 139.6503, 0), degreesInput=TRUE)

# We can now calculate the azimuth and elevation:

razel <- calculateRazel(observer_ITRF, italsat_ITRF, degreesOutput=TRUE)
razel[1] # Azimuth
razel[2] # Elevation