Meaning of GF settings

Jan Schubert Jan.Schubert at GMX.li
Wed Jan 9 15:14:11 PST 2013


On 01/08/13 23:39, Robert C. Helling wrote:
> On Jan 8, 2013, at 6:45 PM, Jan Schubert wrote:
>
>> - It (still) seems to use the ceiling-at-this-very-specific-moment
>> approach, not considering a ascent which explains the ceiling deeper and
>> earlier in the descent phase of the dive. Just a note, it's more
>> important that we get this right for the dive planning part of
>> subsurface. And if we (would) have it there, it should not be that
>> tricky to apply this to this part as well!?
> This would complicate the algebra even more and at least that would not match my understanding of the word "ceiling".
> For the ceiling during the descent part of the dive: For the gradient factors to work one has to use the max depth of the dive (as that is where GF_low applies). The code does not use the global max depth but the max depth up to that point (which is of course the same during ascend where it matters) or a pre-defined depth (20 or 30m) if that is deeper. I don't know what your dive computer does, do you set a target depth manually or can it look into the future? What I want to say is that the gradient factor calculation is not well defined in the early part of the dive. 

I do not see an issue in here, of course we would (!, in case we decide
to do) just use what we have at this specific moment (meaning current
max depth). There is no need for a crystal ball. I thought about a clone
of the existing dive simulating an ascend at max. speed, get the ceiling
depth (if there is still one) and discard the clone. In my understanding
this is what dive computers do and what we need to do for the planning
part also.


>> - In case the calculated deco is not ended when the original profile
>> "surfaces" it might be helpful to extend the time for the profile shown
>> to get the calculated deco ceiling displayed completely (this would
>> allow better playing with existing dives and such parameters as GF).
> Good idea. Which depth would you use for the remaining off-gasing, surface or ceiling (in which case it becomes more akin to dive planning).

Tricky, I'd vote for surface (as is).

> - seeing the smooth profile I'm quite amazed that the non-linearities
> vanished nearly completely, I'd not have expect this before.
> Could you send a screen shot of your dive with smooth ceiling as well? My guess would be that the differences between the dc ceiling and deco.c get smaller (since we always round up to full multiples of 3m).

attached

HTH,
Jan
-------------- next part --------------
A non-text attachment was scrubbed...
Name: ss_smoth.png
Type: image/png
Size: 154015 bytes
Desc: not available
URL: <http://lists.hohndel.org/pipermail/subsurface/attachments/20130110/2f529921/attachment-0001.png>


More information about the subsurface mailing list