Artifacts with VPM-B ceiling on level changes

Robert C. Helling helling at atdotde.de
Thu Aug 27 22:05:10 PDT 2015


Gaetan,

> On 28 Aug 2015, at 05:31, Gaetan Bisson <bisson at archlinux.org <mailto:bisson at archlinux.org>> wrote:
> 
> 
> I've noticed what looks to me like artifacts regarding the ceiling VPM
> calculates for multilevel dives. See the attached screenshot.
> 
> Basically, during manually entered ascent segments, the calculated
> ceiling becomes deeper as the diver goes shallower...

thanks for finding this. I need to look into this. Maybe it is related to another problem with the ceiling namely that it is possible that the profile thinks that a dive computed with the planner violates the ceiling (of course it should not since that is essentially the definition of the ceiling) and turns the profile red. So I know there is something wrong there.

Having said that, there are two other issues: VPM-B as such does not really have a ceiling as the tolerated gradient is adopted to what later happens in the ascent. So the plotted ceiling is anyhow somewhat fake (and not part of the model but added by me).

But even more important: As a model, VPM-B treats the ascent totally different than the bottom part of the dive. For example the transition point is special as some values are computed there (the „bottom pressure“ as well as reference point for the Boyle compensation). We use the end of the manually entered waypoints as this reference point (taking the deepest point in the dive would not be better), so if your manually entered points contain significant ascent parts, you are bound to confuse the model anyway. Maybe we should try to detect his and warn the user.

Best
Robert
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