#!/bin/bash

function usage()
{
  echo "usage: $0 <file> <latitude> <longitude>"
  echo "  Depends on exiftool (from libimage-exiftool-perl)."
  echo "  lat/lon in decimal format [-+][NN.N+]"
  echo "  (lon: east is +, west -; lat: north +, south -)"
  echo
  echo "  <file> must be writable."
  exit 1
}

if ! [ "$3" ] ||
  ! [ -w "$1" ] ||
  ! $(echo "$2" | grep -q -- "^[-+]\?[0-9.]\+") ||
  ! $(echo "$3" | grep -q -- "^[-+]\?[0-9.]\+")
then
  usage
fi

function numpart()
{
  echo $1 | sed -e 's/[+-]\?\([0-9.]*\)/\1/'
}

filename="$1"
latitude=`numpart $2`
longitude=`numpart $3`

if $(echo $2 | grep -q -- "^-"); then
  latref="South"
else
  latref="North"
fi

if $(echo $3 | grep -q -- "^-"); then
  longref="West"
else
  longref="East"
fi

echo "Updating ${filename}: ${latitude} ${latref}, ${longitude} ${longref}"

exiftool \
  -GPSLatitudeRef=$latref \
  -GPSLatitude=$latitude \
  -GPSLongitudeRef=$longref \
  -GPSLongitude=$longitude \
  "${filename}"