Tank pressure plots for CCRs

Rodrigo Severo rodrigo at fabricadeideias.com
Mon Jan 6 14:01:40 UTC 2014

On Mon, Jan 6, 2014 at 7:44 PM, Dirk Hohndel <dirk at hohndel.org> wrote:

> On Mon, 2014-01-06 at 19:27 -0200, Rodrigo Severo wrote:
> > Item 1 isn't so simple as I believe any change to implement it will
> > affect lots of code inside profile.c but it seems to me more as
> > lots-of-work, not really-hard-work.
> Tomaz is rewriting the profile system right now. This might be a great
> time to make sure that the real requirements for this are well
> understood.
> One caveat - Subsurface has always been open to cater to specific
> subsets of the user base, but we have a hard rule that we cater to the
> "typical recreational diver" first. So we will not make changes that
> make Subsurface less useful for recreational OC divers just because the
> few suicidal people who dive rebreathers think that's what they need.

I see you don't trust rebreathers very much ;)

But I don't see why these changes would make Subsurface any less useful for
recreational OC divers. As I mentioned the extra step of defining a tank
pressure segment as OC, CCR O2 or CCR diluent should be optional with the
default being OC obviously. AFAICT there would be no difference here for
recreational OC divers.

> Implementing item 1 could also have the positive side effect of fixing
> > the gaps that consecutive tank pressure plots for the same tank
> > present. The last pressure of a tank pressure line is always higher
> > than the first pressure of the next line for the same tank. They
> > should be exactly the same. These gaps exist now with the current code
> > and also with my yet not approved nor refused patch "Discontinuity and
> > stall on tank pressure interpolated lines". I would never suggest that
> > a change so big as item 1 implies be done just because of these gaps
> > but I think it would be great to fix this too.
> Actually, there is no such thing as "it should be the same". Pressure
> data can fluctuate for many reasons and it's entirely possible that
> pressure has gone up because the diver crossed a thermocline. Or
> pressure could have gone down because of leakage.
> Since pressure data is NOT continuous but assembled from discrete
> samples there can and will be sudden changes.

You are completely right when we have discrete samples for the dive.

I was talking about interpolated tank pressure plots, like when we have
only the start and end tank pressures for the whole dive. In this situation
the last pressure of a tank pressure line should be exactly the same as the
first pressure of the next line for the same tank. There is no reason for
us to interpolate otherwise. In fact both current code and my patch do the
right thing in this aspect. It just isn't plotted correctly because current
code only plots one tank pressure point per sample.

I should have been clearer. Sorry for the confusion.

Rodrigo Severo
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