R/sunLocation.R

In michaeldorman/shadow: Geometric Shadow Calculations

# Function to create a 'SpatialPointsDataFrame' object representing sun location

.sunLocation = function(location, sun_az, sun_elev) {

  # Conditions
  stopifnot(class(location) %in% c("SpatialPoints", "SpatialPointsDataFrame"))

  # Average earth-sun distance in meters
  dist_m = 149.6 * 10^9

  # To radians
  az_rad = deg2rad(90 - sun_az)
  sun_elev = deg2rad(sun_elev)

  # Sun height
  height = data.frame(height = dist_m * tan(sun_elev))

  # Attribute table
  if(is(location, "SpatialPointsDataFrame"))
    data = cbind(location@data, height) else
      data = height

  # Sun location
  sp::SpatialPointsDataFrame(
    coords = raster::shift(location, dist_m * cos(az_rad), dist_m * sin(az_rad)),
    data = data
  )

}