Today I had a Navman iCN320 sat nav come my way.
After a brief look it seems that the crucial three files are within the SYSTEM directory:
RECENT.DAT stores up to thirty of the recently navigated to destinations. These destinations are stored in records of 520 bytes in length. Each destination has its Lat/Long coordinates stored in 8 bytes starting at Record Offset 507. These are decoded by bookmarking in Encase as a 32 bit integer. In the UK Latitude will begin in the range 49-59 and is decimally notated. Longitude is in the range -5 to +1.6 ish. When bookmarking as a 32 bit integer Longitude is shown first and will often be a negative value (i.e. anywhere west of Greenwich).
FAVVER4.DAT possibly stores up to 200 user entered favourite destinations. These favourite destinations are stored in records of 1508 bytes in length. Each destination has its Lat/Long coordinates stored in 8 bytes starting at Record Offset 352. These are also decoded by bookmarking in Encase as a 32 bit integer.
ROUTE.DAT I speculate is used to store the origin of the last navigated journey. Coordinates can be found at record offset 507.
GREP search expression for Encase ......[\x4f-\x55]\x00
Looks like a bit of testing is in order!