Hi Colm,
Sorry to have to say this, but I’m pretty sure what you are suggesting is impossible.
The only way a Raspberry Pi can directly access the Internet is via an external router or Hotspot (such as a mobile phone or other 4/5G device). Linking with a raw Pi2 is limited to Ethernet by cable. The Pi3B (which is used in Rosetta) has its own inbuilt WiFi which can under certain circumstances (e.g. when used in a base station) be set up to connect direct to the Internet by WiFi via an external router or hotspot, but even the Pi3 can’t provide both a Data Source ‘Hotspot’ which we need to provide GPS and Traffic Data to your Display, and an external internet connection at the same time.
The problem I’m afraid lies with the developers of the newer versions of the Tablet / Phone firmware, who in their wisdom and increasing fear of allowing unrecognised data sources to access your device, seem to have removed the option to connect to two different external sources via WiFi and Bluetooth at the same time. Not at all helpful I’m afraid, but probably something we will have to learn to live with. Unless someone else out there knows different??
Regards
Peter