Convert Horizontal Coordinates to Cartesian Vector

Given apparent angular horizontal coordinates, calculates a horizontal Cartesian vector.

Given apparent angular horizontal coordinates, calculate horizontal vector. The input azimuth is measured in degrees clockwise from north (east = +90). The returned vector is in the horizontal system: x = north, y = west, z = zenith (up).

Usage

astro_vector_from_horizon(sphere, time, refraction = 1L)

astro_vector_from_horizon(sphere, time, refraction = 1L)

Arguments

sphere

A list with components:

lat

Refracted altitude angle in degrees

lon

Azimuth in degrees clockwise from north

dist

Distance from the observer to the object in AU

time

POSIXct time of the observation

refraction

Refraction option (0 = REFRACTION_NONE, 1 = REFRACTION_NORMAL, 2 = REFRACTION_JPLHOR). This specifies how refraction is to be removed from the altitude stored in sphere$lat.

Value

A list representing a horizontal Cartesian vector with elements:

• x: North component in AU

• y: West component in AU

• z: Zenith (up) component in AU

• t: Time value

• status: Status code (0 = success)

A list representing a vector in the horizontal system with components:

x

North component in AU

y

West component in AU

z

Zenith (up) component in AU

t

The date and time (POSIXct)

status

Status code (0 = success)

Examples

# 30° altitude, facing south
hor <- list(lat = 30, lon = 180, dist = 1)
time <- as.POSIXct("2024-01-01 12:00:00", tz = "UTC")
vec <- astro_vector_from_horizon(hor, time, refraction = 1)

# Convert horizontal coordinates to vector
sphere <- list(lat = 45, lon = 90, dist = 1)  # 45° altitude, 90° azimuth (east)
time <- as.POSIXct("2024-01-01 12:00:00", tz = "UTC")
vec <- astro_vector_from_horizon(sphere, time, refraction = 1)