Re: [gpsd-dev] Note on climb error modelling

[Pavel Kirienko]

Sure.
Here is how it is being computed now:

epc = (epv_old + epv_new) / dt

Obviously this equation implies that EPC depends on the solution
update rate (inversely), and it is unclear why. Assuming that most
(all?) receivers have no gradual accuracy drop with higher update
rates, this equation looks invalid.
I am aware that a similar approach is used for EPS computation and I
consider it incorrect too, but so far I have no better ideas to offer
so let's stick to EPC only.

My approach assumes that EPC is always close to EPS for any given
instant, because this holds for EPV and EPX/Y.

Pavel.

On Sat, Nov 30, 2013 at 9:31 PM, Eric S. Raymond <address@hidden> wrote:
> Pavel Kirienko <address@hidden>:
>> 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.
>
> Before I change yjthe error modeling, break all our regression tests,
> and break backwards compatibility, I will need to see a *principled reason*
> for the change - not just an ad-hoc patch.
>
> That is, you need to argue that the new formula is physically and
> geometrically reasonable.
> --
>                 <a href="http://www.catb.org/~esr/";>Eric S. Raymond</a>