#!/opt/mbari/bin/ruby
epoch = Time.utc(2014,5,11,14,23,55)
timeFmt = '%Y-%m-%d%Z%H:%M:%S'

unless ARGV.empty?
  STDERR.puts <<END
Output track of time and corresponding lat/long coordinates
derived from IridiumLocation entries in on STDIN
lat/long output in decimal degrees (positive North East)
Environment:
  TZ may be set to override the timezone
Example:
  curl -s ftp://espshore/moe/esp/messages | TZ=CDT iridiumTrack
END
  exit 2
end

include Math
DegPerRad = 180/PI
A = 6378.137
B = 6356.7523142451
b2 = B*B
a2 = A*A
a2lessB2 = a2 - b2
E2 = a2lessB2 / a2
Eprime2 = a2lessB2 / b2

loc = /\s+IridiumLocation:\s*(-?\d+),(-?\d+),(-?\d+),([0-9a-f]+)/i
STDIN.each do |logLine|
  if match = loc.match(logLine)
    tics = match[4].hex
    begin
      print((epoch+0.09*tics).getlocal.strftime timeFmt) if tics != 0
      x,y,z = Integer(match[1]), Integer(match[2]), Integer(match[3])
      p = sqrt(x*x + y*y)
      theta = atan2 A*z, p*B
      lat = atan2(z + Eprime2*B*sin(theta)**3, p - E2*A*cos(theta)**3)*DegPerRad
      long = atan2(y,x) * DegPerRad
      print '   %.3fN  '%lat, "%.3fE\n"%long
    rescue =>err
      print err.inspect, " on log line ", STDIN.lineno, "\n"
    end
  end
end