A triangular shipment is usually used to keep the actual suppliers name hidden from the actual consignee. This will involve 3 parties with documentation swaps at one point during the business transaction.

Referring to the above graphic.

Let us fix the following, (A) being the factory in Germany (B) being the buyer / trader in Singapore (C) being the actual receiving party in Australia.

There are two separate PO’s in place.

PO 1: Between (B) and (A) 
PO 2: Between (C) and (B)

Looking at the actual cargo movement.

Option 1: (B) will request (A) to send the cargo directly from Germany to Australia. This is only if (B) can share with (C) that the origin of the goods is Germany.

Option 2: (B) will request (A) to send the cargo from Germany to Singapore. Thereafter (B) will need to book a vessel from Singapore to Australia for (C) to receive the cargo. In this case (C) will not be able to know that the goods are coming from Germany.

Now let us look at the documentation portion.

We will have 2 x Sets of documents which will include a switch of documents in Singapore (C).

Document set 1: Packing List / Commercial Invoice / HBL / MBL between (A) and (B)
Document set 2: Packing List / Commercial Invoice / HBL / MBL between (B) and (C)

Below you will see who the supplier / shipper and buyer / consignee for each of the document sets is.  

Document set 1: 
Supplier / Shipper: (A)
Buyer / Consignee: (B)

Document set 2:
Supplier / Shipper: (B)
Buyer / Consignee: (C)

NOTE: POL and POD usually cannot be changed unless using a Dummy HBL between (A) and (B) showing the POL as Germany and the POD as Singapore. 
Shipping Lines are OK to change the Shipper and Consignee on their MBL against signed and endorsed LOI (letter of indemnity)