Cache the parsed navigation and airport data in a binary file to reduce
startup times and memory consumption (since only referenced FGPositioned
elements are held in memory).
Data will be reimported when the mod-time of any input file is changed.
If a global file is changed (nav.dat, awy.dat, apt.dat, etc), the cache
will be completely rebuilt, which takes approximately 30 seconds on
moderate hardware. (Future work may reduce this).
instrument of the same name. In the future I'd prefer to rename the
instrument class instead (FGMarkerBeaconReciever?) but this is the safest
change for now.
Thanks (again) to Yon Uriarte for pointing out the problem (which seems to
affect MSVC more than gcc)
saving for beacons, but since they're surprisingly few (in nav.dat), not a
an enormous saving in real terms. The major motivation is that marker beacons
don't behave like other NavRecords for radio interaction - they have no ident,
frequency or range (in the sense that NavRecord means them).
