Meaning of GF settings

[Jan Schubert]

On 01/05/13 17:35, Dirk Hohndel wrote:
> Jan Schubert <Jan.Schubert at GMX.li> writes:
>> Oh forgot to put some notes to Dirks question about the "odd shape" of
>> the deco ceiling curve: When calculationg the deco ceiling all the 16
>> tissue compartments has to be taken into account. The deco ceiling is
>> defined by the compartment/tissue having the highest overpressure,
>> called the leading tissue. This leading tissue can (and will!) switch
>> during a dive resulting is such mentionable jumps (ups  and downs) when
>> looking at the smooth deco ceiling curve not based on 3m steps. 
> That part I understand - what surprised me is how drastic these steps
> are. It seems as if there still is a 3m step hidden in the code
> somewhere... and I already found where... it's in the GF adjustment
> code:
>
> 	new_gradient_factor = gradient_factor_calculation(&mydata);
> 	below_gradient_limit = (new_gradient_factor < actual_gradient_limit(&mydata));
> 	while(!below_gradient_limit)
> 	{
> 		mydata.pressure += PRESSURE_CHANGE_3M;
> 		new_gradient_factor = gradient_factor_calculation(&mydata);
> 		below_gradient_limit = (new_gradient_factor < actual_gradient_limit(&mydata));
> 	}
> 	depth = rel_mbar_to_depth((mydata.pressure - surface_pressure) * 1000, dive);
> 	return depth;
>
> So while we do the smooth calculation for most of the time, the GF
> pushes us into 3M changes... I think I'll play with a modification that
> does the loop here with 1M increments if we are in 'smooth' mode.
>
> Do you think that would be useful, Jan?


1m ist still to much to be considered smooth in my humble opinion. Why
not use 0,1m instead? And of course you should stick to 3m when doing
the NonSmooth mode.



>
> What is missing at this point:
>
> - UI

Yeah would be nice. We should allow to configure several parameters
there which are now fixed. F.i. surface pressure is set to 1013mbar
several times, in my regions we use to have around 940-970mbar (which
would make some difference for deco calculation). Of course I've seen
that this could be changed in planner.c.

Please also note that there is also a safety_dist_deco_stop of 0,5m
defined in deco.c from the DR5. This is not used so far from what I've
seen but if we do in future calculations this should also be a
configurable parameter (like in the OSTC firmware).

> - gas use prediction based on SAC rate (for OC folks)

Very important part, also for CC bailout calculation. Note: It is common
to differ between a (higher) bottom SAC and a (lower) deco SAC. And then
it would make sense to have a link to the tanks used and defined in
subsurface and previous dives (which I never used so far).

> - printing of tables (with big disclaimer on them)
>
> and then maybe
>
> - multiple deco algorithms

Would be appreciated very much!

> - better ability to compare between them

Thx a lot Dirk,
Jan