I would use something like this:
# Retrieve the full pathname of the called script
scriptPath=$(which $0)
# Check whether the path is a link or not
if [ -L $scriptPath ]; then
# It is a link then retrieve the target path and get the directory name
sourceDir=$(dirname $(readlink -f $scriptPath))
else
# Otherwise just get the directory name of the script path
sourceDir=$(dirname $scriptPath)
fi