R/interp.axis.R

In mhweber/spsurvey: Spatial Survey Design and Analysis

################################################################################
# Function: interp.axis
# Programmers: Tony Olsen
#              Tom Kincaid
# Date: March 26, 2007
# Last Revised: April 26, 2007
#
#' Create Right-Side y-Axis Lables for a CDF Plot
#'
#' This function creates right side y-axis labels for a CDF plot.  It assumes
#' that arguments cdfest.l and cdfest.r are strictly increasing.  If argument
#' yl.lab is less than the first cdfest.l vlaue, then the funciton assumes 0 for
#' both cdfest.l and cdfest.r.
#'
#' @param yl.lab Vector of left side y-axis labels, which are the basis for
#'   interpolating cdfest.r values.
#'
#' @param cdfest.l Vector of CDF estimates corresponding to the left side
#'   y-axis.
#'
#' @param cdfest.r Vector of CDF estimates corresponding to the right side
#'   y-axis.
#'
#' @return A numeric vector consisting of the right side y-axis labels.
#'
#' @author
#'   Tony Olsen \email{Olsen.Tony@epa.gov}\cr
#'   Tom Kincaid \email{Kincaid.Tom@epa.gov}
#'
#' @export
################################################################################

interp.axis <- function(yl.lab, cdfest.l, cdfest.r) {

nvec <- 1:length(cdfest.l)
rslt <- numeric(0)
for (j in 1:length(yl.lab)) {
   high <- ifelse(length(nvec[cdfest.l >= yl.lab[j]]) > 0,
                  min(nvec[cdfest.l >= yl.lab[j]]), nvec[length(nvec)])
   low <- ifelse(length(nvec[cdfest.l <= yl.lab[j]]) >  0,
                 max(nvec[cdfest.l <= yl.lab[j]]), NA)
   if(is.na(low)) {
      ulow <- 0
      plow <- 0
      pdis <- (yl.lab[j] - plow)/(cdfest.l[high] - plow)
    	 rslt[j] <- ulow + pdis * (cdfest.r[high] - ulow)
   } else {
      if( high > low) {
    	    pdis <- (yl.lab[j] - cdfest.l[low])/(cdfest.l[high] - cdfest.l[low])
    	    rslt[j] <- cdfest.r[low] + pdis * (cdfest.r[high] - cdfest.r[low])
      } else {
         rslt[j] <- cdfest.r[high]
      }
   }
}

return(rslt)
}