Rutils/maybe-not-useful/poly.clockwise.r

In manfredo89/ED2io: Manages Input/Output for Ecosystem Demography 2 Model

#==========================================================================================#
#==========================================================================================#
#     Polygon in clockwise direction.                                                      #
#------------------------------------------------------------------------------------------#
poly.clockwise <<- function(x,y=NULL){
   #----- Check whether y is null or is given as data frame. ------------------------------#
   if (is.null(y)){
      #----- Find x and y. ----------------------------------------------------------------#
      ix = which(names(x) %in% c("x","X"))
      iy = which(names(x) %in% c("y","Y"))
      y  = x[[iy]]
      x  = x[[ix]]
      #------------------------------------------------------------------------------------#
   }else if (length(x) != length(y)){
      stop("x and y must have the same length!")
   }#end if
   #---------------------------------------------------------------------------------------#


   #------ Make sure this is a closed path. -----------------------------------------------#
   nxy  = length(x)
   if (! ( x[1] %==% x[nxy] && y[1] %==% y[nxy] ) ){
      x   = c(x,x[1])
      y   = c(y,y[1])
      nxy = nxy + 1
   }#end if (! ( x[1] %==% x[nxy] && y[1] %==% y[nxy] ) )
   #---------------------------------------------------------------------------------------#


   #---------------------------------------------------------------------------------------#
   #     Normalise the coordinates to reduce numerical erros whilst finding the            #
   # determinant of the orientation matrix.                                                #
   #---------------------------------------------------------------------------------------#
   xyscale = max(diff(range(x,finite=TRUE)),diff(range(y,finite=TRUE)))
   xnorm = ( x - min(x,na.rm=TRUE) ) / xyscale
   ynorm = ( y - min(y,na.rm=TRUE) ) / xyscale
   #---------------------------------------------------------------------------------------#



   #---------------------------------------------------------------------------------------#
   #    Find the sum of the ratio of differential x and sum of y.                          #
   #---------------------------------------------------------------------------------------#
   aa      = sequence(nxy-2)
   bb      = aa + 1
   cc      = aa + 2
   deto    = ( (xnorm[bb] - xnorm[aa])*(ynorm[cc]-ynorm[aa])
             - (xnorm[cc] - xnorm[aa])*(ynorm[bb]-ynorm[aa]) )
   orient  = sum(deto,na.rm=TRUE)
   #---------------------------------------------------------------------------------------#


   #---------------------------------------------------------------------------------------#
   #    Revert the polygon if it is anti-clockwise.                                        #
   #---------------------------------------------------------------------------------------#
   if (orient >= 0.0){
      ans = data.frame( X = rev(x), Y = rev(y) )
   }else{
      ans = data.frame( X = x     , Y = y      )
   }#end if
   #---------------------------------------------------------------------------------------#


   #----- Return the answer. --------------------------------------------------------------#
   return(ans)
   #---------------------------------------------------------------------------------------#
}#end function poly.clockwise
#==========================================================================================#
#==========================================================================================#