Just refreshing my memory on GPSGate...
When I looked at it some years ago, it was a very interesting and promising
concept. Maybe
cheap AIS did overtake it a bit on the
water, but it has been well worth some attention. However, I do not know the
current status of Franson
software and services offering.
Briefly, it works as follows:
Many targets can report their position via multiple channels to some organization, hosting a GPSGate Server. It can be over
Internet apps and - most notably - from a mobile
phone over SMS
service.
The server keeps a database of position reports.
The database can be interrogated by a client in two basic ways.
One type of request addresses a specific target. The response then takes form of a
single RMS sentence, without identification, because this is already well known from the query context.
Another type of request addresses a "Buddy Group" - a predefined set of targets. The response then takes form of a series of FRPOS statements, similar to RMS, but extended with target identification and other details, not present in
NMEA RMS.
So, depending on whether one makes an individual or a group query, the stream of responses contains just RMS or just FRPOS sentences.
GPSGate Server and Client is not free, so I was not in a position to comfortably set up a test site. I just implemented the obvious: handling of FRPOS sentences, piggybacking on the existing
AIS subsystem. I left out the login/authentication and active interrogation part until having a real test
bed and gaining some experience. (That was in 2010...)
GPSGate targets differ from AIS targets, mainly because they do not age so easily. The position reports may come irregularly, and not so often - even once per day or so ... Some of the reports, I am not sure which, indicate only positions that had changed since the last interrogation. So directly translating FRPOS into AIVDM is not always right.
Tracking GPSGate Buddies has been fully implemented in some chartplotters. One example is SOBvMAX from Digiboat.
I do not think now that there is a need to put more effort into this. However, there would be 3 ways to move forward:
1. Implement full GPSGate Client into OCPN or a
Plugin.
2. Write a small connector program to perform the login and interrogation, passing back the FRPOS responses to OCPN.
3. Find a way to use existing GPSGate
software to perform these tasks.
If I were an actual user, I would start from investigating choice #3.
Choice #2. is still a possibility.
I feel it is still too early for choice #1.
Notably, many users use GPSGate Client software just as a connectivity tool, not using the Server protocol at all, just routing
NMEA between various transports ...