[gpsd-dev] Note on climb error modelling

[Pavel Kirienko]

Seems that usually gpsd's error modelling logic yields too high EPC
values if compared to the typical GPS speed precision; especially in
cases when the solution update frequency is higher than 1 Hz (for
reference, EPC is currently being computed as (old_epv + new_epv) /
dt).

I can't propose a better approach for error modelling now, but we can
reuse EPS for EPC. I.e. if a receiver provides EPS and not EPC,
assumption EPS = EPC seems to be justifiable.

Pavel.