R/sun.zen.R

In DGampe/TriangleMethod: Calculation of NDVI, LST and finally provide an estimation for actual evapotranspiration patterns using remote sensing data (default LANDSAT TM and ETM+ scenes).

sun.zen = function(ras,time, crs.code = CRS("+init=epsg:4326"),...){

  ras.grid = suppressWarnings(as(ras,"SpatialGridDataFrame"))
  gc()
  ras.trans = suppressWarnings(spTransform(ras.grid, CRS = crs.code))
  lat = mean(ras.trans@coords[,2])
  lon = mean(ras.trans@coords[,1])
  act.tm = solar(as.POSIXct(time))
  zen = suppressWarnings(zenith(act.tm, lat, lon))
  gc()
  rm(lat,lon,ras.grid)
  return(zen)

  invisible(y)
}