how to use polycube-network to replace iptables nat masq ??

[pipul]

iptables:

iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

polycube:
https://github.com/polycube-network/polycube/blob/master/src/services/pcn-nat/test/test_tcp_masq.sh
polycubectl nat add nat1
polycubectl router add r1

polycubectl router r1 ports add to_veth1 ip=$to_veth1_ip/24 peer=veth1
polycubectl router r1 ports add to_veth2 ip=$to_veth2_ip/24 peer=veth2

polycubectl attach nat1 r1:to_veth2 position=first

polycubectl nat1 rule masquerade enable

i don't understand what is the router use for
this example seem complicated for me