R/maxdev.R

In mousetrack: Mouse-Tracking Measures from Trajectory Data

# # find general equation of the straight line

.packageName <- 'mousetrack'

maxdev <- function (x,y) {

  xchange = x[1]-x[length(x)]
  ychange = y[1]-y[length(y)]
  slope = ychange/xchange
  intercept = y[1] - slope*x[1]

  ## find point on the straight line that has the same x
  ## as the real point

  points = cbind(x, y)
  points.straightline = cbind(x, slope*x + intercept)
  d = sqrt((points[,1] - points.straightline[,1])^2 + (points[,2] - points.straightline[,2])^2)
 
  ## get the corresponding signs for the deviation +/-
  ## the x point on the straight
  y.diff = points[, 2] - points.straightline[, 2]
  signs = sign(y.diff)
  
  ## find the absolute deviations
  ## abs_devs = d;
  abs.devs = d*cos(atan(slope))

  ## re-attach sign to maximum deviation
  indx = match(max(abs.devs), abs.devs)
  max.dev = max(abs.devs) * signs[indx]
  
  return(max.dev)
}