#! /usr/bin/gawk -f 
# Last edited on 2023-09-19 09:06:39 by stolfi

# Reads a file "{IMGNAME}.ipts" with coordinates of four reference points
# named "P0" through "P3" or "Q0" through "Q3".  Writes to standard output
# one line with the average distance between all six pairs of those points.

BEGIN { 
  split("", x)
  split("", y) 
}

/^[PQ][0-3]/{ 
  i = substr($1,2,1)+0 
  x[i]=$2 
  y[i]=$3
}

END{ 
  sd = 0
  for (i = 0; i < 4; i++) {
    for (j = 0; j < i; j++) {
      dx = x[i]-x[j] 
      dy = y[i]-y[j]
      sd += sqrt(dx*dx + dy*dy)
    }
  }
  printf " %6.1f\n", sd/6
}