resolver how does it work
You might also want to do a search on LVDT (linear variable differential transformer) which is basically a resolver in a linear form. Its output is in DC form, although it's driven with AC. If you want any good resolution you'll need good low-noise amplifiers and AD converters, among many other things.
Perhaps the way to go would nowadays be to use either an absolute encoder with enough bits or an incremental encoder with enough lines, plus an index signal for accurate reference point calibration.
If you can't achieve enough resolution with an incremental encoder disc, you can probably place another sensor head adjacent to the existing one, plus some XOR logic to double the resolution. The placement of the second sensor head is critical, but it can be done.
One good manufacturer of absolute encoders is Stegmann.
Just my 2 euroCents,
Hobbie