Solar vector

Computes a unit vector in the direction of the sun based on the solar azimuth and zenith angles.

Usage

sun_vector(zenith, azimuth)

Arguments

zenith

SpatRaster or numeric. Solar zenith angle in degrees.

azimuth

SpatRaster or numeric. Solar azimuth angle in degrees.

Details

Given the spherical coordinates (radius = 1, zenith, and azimuth angles), the sun_vector() function gives the (x, y, z) coordinates of a unit normal vector pointing towards the sun, where the X-axis is positive eastwards, the Y-axis is positive southwards, and Z along the Earth radius and positive upwards (Corripio 2003) .

References

Corripio JG (2003). “Vectorial algebra algorithms for calculating terrain parameters from DEMs and solar radiation modelling in mountainous terrain.” International Journal of Geographical Information Science, 17(1), 1–23. doi:10.1080/713811744 .