How Zora chooses a source

What Zora does with a source priority, and what it does for the GPS on its own. Setting the order is in Source priorities.

With no order

A value with two sources and no order takes whichever source sent last. With two GPS receivers a few metres apart, the boat's position jumps between them.

With an order

Zora uses the first source while it sends. When it goes silent for as long as the next source's timeout, the next source takes over, and so on down the list.

A GPS receiver has the same timeout on every GPS value it sends. When it goes silent, its position, course and speed move to the backup together, so the position never comes from one receiver and the course from another.

Zora ranks new receivers itself

On a boat where nobody has set a GPS order, Zora sets one: a dedicated GPS before the receiver inside a VHF or an AIS, then by the quality of the fix each reports.

A receiver that arrives later, for example one plugged in at the dock, is added to the end of the order within about a minute, with no restart. Zora never rearranges an order you have set. Only Reassess does, and only when you ask.

Zora drops a receiver with a bad fix

A timeout only helps when a receiver goes silent. A receiver can go on sending with a lost or poor fix, so Zora also watches what each receiver reports about its own fix:

• the receiver in use reports no fix for 10 seconds, or
• it reports an HDOP above 5 for a minute, and another receiver's is at least 2 lower.

Zora then moves the boat's GPS values to the best receiver that has a fix, and shows a warning, GPS source changed, naming the receiver it now uses. The warning makes no sound and stays until the dropped receiver recovers.

Once that receiver has reported a good fix for 3 minutes, Zora goes back to your order and the warning clears. The GPS tab shows your order throughout.