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I'm curious about ICAO naming conventions regarding GNSS and RNAV waypoints. Would I be correct in assuming that all GNSS area waypoints are 5 letters, and RNAV waypoints are 6?
What about waypoints like CB401? Do these represent a reference to a VOR/DME? If so, why are they included in GPS waypoint databases?
The only 6+ letter designator I'm aware of (for a waypoint; not a procedure) is the contracted version of a plain language point marked by a radio nav aid.
The example in Annex 11 is the contraction of FUERSTENFELDBRUCK to FURSTY.
c) the name should, if possible, consist of at least six letters and form two syllables and preferably not more than three;
As for the "coded" designators you're referring to, Annex 11 references Doc 8168 Vol 2 for the "Waypoints used in support of RNAV SIDs, STARs and instrument approach procedures" (NB: GNSS included). Of the criteria:
b) the five-alphanumeric name-code should consist of no more than three numbers with the alphabetic characters being taken from the airport designator;
c) the convention and the rules of application shall be published in the State AIP;
d) the five-alphanumeric name-code shall be unique within the terminal area in which it is used;
Check if indeed your CBxxx example borrows the CB from the airport's designator. And reference the local AIP for the local rules.
(All bold emphasis mine.)
Possibly related depending on the waypoints you've seen: What are those 5-character alphanumeric waypoints? (High Altitude Redesign program.)
There are no "GNSS waypoints". GNSS is a common position source for RNAV, though not the only one.
All RNAV waypoints, like conventional (e.g. VOR/DME) fixes, have an identifier composed of five alphanumeric characters that is unique within a country. Some countries don't use numbers (e.g. the US); others do.
