R/directionCosines.R

In LatticeKrig: Multi-Resolution Kriging Based on Markov Random Fields

# LatticeKrig  is a package for analysis of spatial data written for
# the R software environment .
# Copyright (C) 2016
# University Corporation for Atmospheric Research (UCAR)
# Contact: Douglas Nychka, nychka@ucar.edu,
# National Center for Atmospheric Research, PO Box 3000, Boulder, CO 80307-3000
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.

directionCosines<- function( x){
# x is lon/lat in degrees
# x[,3] if there is the radial component
     coslat <- cos((x[, 2] * pi)/180)
     sinlat <- sin((x[, 2] * pi)/180)
     coslon <- cos((x[, 1] * pi)/180)
     sinlon <- sin((x[, 1] * pi)/180)
# if just 2 d then assume the points are on sphere
# if dim >= 3 then include the radial component.
if( ncol(x)==2){
return( cbind(coslon*coslat, sinlon*coslat, sinlat))
}
else{
	return( x[,3]*cbind(coslon*coslat, sinlon*coslat, sinlat))
}
}