Subsurface minimum gas calculation - First version for review

Pablo Wolter pwolter at
Tue Feb 21 17:00:46 PST 2017

I can help testing this as I'm familiar with the Minimum deco or Rock
bottom gas management.

If you send me a link to your branch I can look at it and try to break it.


On Tue, Feb 21, 2017 at 14:04 Stefan Fuchs <sfuchs at> wrote:

> Hello Robert, hallo Dirk,
> Am 21.02.2017 um 11:44 schrieb Robert Helling:
> Stefan,
> On 21.02.2017, at 11:02, Stefan Fuchs <sfuchs at> wrote:
> the problem is that for computers that don’t have gas information, the
> interpolation of cylinder pressures is only done at the plot stage. The
> information is in struct plot_data which you find in profile.h, in
> particular in cylinderindex and pressure[2] (to access the latter there is
> a macro, for usage see profile.c. Strictly speaking, that is to handle the
> CCR case which you want to avoid anyway but it’s better to use this as an
> accessor).
> Hmmm... plot_data is rather difficult to access from planner.c. Or do I
> miss any easy way to do this?
> Hmm. That’s true. Problem is: during planning, so far, we don’t track gas
> usage but compute it only later. Concretely, in planner.c
>  static void create_dive_from_plan(struct diveplan *diveplan, bool track_gas)
> close to the bottom there is
> 			update_cylinder_pressure(&displayed_dive, sample[-1], depth, time - sample[-1].time.seconds,
> This might be a place where one could inject a test if rock bottom is
> exceeded if that value is already known at that stage. Alternatively, you
> might have to store the pressure vs time information or you store the rock
> bottom value for the gas with the dive and generate the warning only in the
> plotting stage (close to where the gas pressure curves are created).
> Thinking about this, I guess the latter is what I would go for.
> For the moment I have to stop here because I will be on holiday for a week
> soon and this part for sure will need approximately 1-3 years development
> time on my side ;-)
> What do you think about the part of the minim gas calculation we created
> up to now?
> Is it already time to do a pull request to maybe have some deeper testing
> or do we need to continue testing and review internally?
> Tomorrow I may be able to write a few words about this feature for the
> user manual. Shall I put user manual updates in a separate commit (I assume
> yes)?
> Best regards
> Stefan
> --
> Stefan Fuchs
> E-Mail: sfuchs at
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