git bisect vs libdivecomputer interface

[Anton Lundin]

On 10 January, 2017 - Robert Helling wrote:

> Hi,
> 
> > On 10.01.2017, at 14:01, Anton Lundin <glance at acc.umu.se> wrote:
> > 
> > I don't have a solution to your libdivecomputer issues, but other
> > goodies.
> > 
> > I saw the issue you created and got a idea, and found a probable
> > explanation for the issue.
> > 
> > It looks to be the pressure / volume calculations work done by Linus who
> > "broke" the sac-tests. The sac-tests are planned for a ideal gas, but
> > now when we do better sac calculations, we're off by a bunch.
> > 
> > The proper fix would probably to fix pressure-track-code to use real
> > volumes and not ideal gases, and also fix the sac-test.xml pressures to
> > match with reality.
> 
> 
> you were spot on. When I make gas compressibility factor always return 1.0, I get back the 20l/min SAC.
> 
> Which worries me a bit: I am surprised that the effect of using real gas compressibility vs ideal gas law makes such a difference. 18.5 vs 20 is an 8% difference in SAC rate!

Even if its 8%, more or less, we should change so the
populate_pressure_information() works with volumes instead of
pressures. That would get the calculations to match up, and get rid of
the ugly sac-rising weirdness we currently are seeing.


I have had "debug this sac-rising weirdness" on my todo-list for quite
some time, but I never got around to actually look at it. Its great that
we now know what the source of this weirdness is.


//Anton


-- 
Anton Lundin	+46702-161604