From JDiveLog to Subsurface

[Jef Driesen]

On Mon, 31 Oct 2011 07:45:24 -0700, Linus Torvalds wrote:
> On Mon, Oct 31, 2011 at 7:04 AM, Jef Driesen <jefdriesen at telenet.be> 
> wrote:
>>
>> The Suunto Vyper series only stores the temperature and tank 
>> pressure before
>> and after the dive, and also the temperature at the maximum depth.
>
> I didn't even realize that they were air-integrated at all. At least
> giving the start/end pressure is better than not having it at all.

It depends on the model. The Cobra is definitely air integrated and I 
think the Vytec too (when using the wireless transmitter).

> The jdivelog file doesn't seem to have those pressures, though - at
> least not in a format that looks like it came from a dive computer.
> The pressures it has seem to be entered by hand, because they are so
> round (eg "PSTART 2.2E7, PEND 8000000" - almost certainly in pascal,
> and thus looks very much like 220 bar down to 80 bar to me, and is
> unlikely to be a computer reading).

Manual entered data sounds plausible.

>> You can easily notice this when you click the recalculate button in 
>> the Air
>> Consumption tab. It will ask you whether to simulate or not. 
>> Depending on
>> whether you answer yes or no, SDM will interpolate the pressure 
>> linearly
>> (and thus a non constant SAC graph), or interpolate the pressure 
>> assuming a
>> constant SAC (and thus a non linear pressure graph). Note that SDM 
>> will ask
>> this question only once (per dive), and you can't undo your choice 
>> as far as
>> I know.
>
> Ok. We always interpolate pressures with a constant-SAC model, and
> paint the interpolated line in yellow (while actual samples are in
> green)

I agree the constant SAC method is the preferred option. A linear 
pressure interpolation doesn't make much sense.