A disk image can be created using the following commands:
$> truncate -s 1200M ./disk.raw
-$> echo -e "label: gpt\n,64M,U\n,,L" | /usr/sbin/sfdisk ./disk.raw
+$> echo -e "label: gpt\n,64M,U\n,,L" | /usr/sbin/sgdisk ./disk.raw
$> lodev=`sudo losetup -P -f --show ./disk.raw`
$> sudo mkfs.vfat -n EFI -v ${lodev}p1
$> sudo mkfs.ext4 -L ROOT -v ${lodev}p2