Planner: Multiple Deco calculations ?

[JB2Cool]

The website for the VPM algorithm is here http://www.decompression.org.
There are a few resources there along with some open source implementations
that could be looked at as a basis of the code.

My belief is that if you wanted to compare a variety of different
algorithms and all of their different variants then use a dedicated
dive-planner software package (I myself use MultiDeco and Pastodeco). If
you want a diving logbook with a built-in, tried and tested dive planner
using pretty much the widest used algorithm then use Subsurface. When i
first started planning dives there was lots of talk about VPM and it seemed
very popular but since then i've noticed a steady shift to Bühlmann +
Gradient Factors.

The Bühlmann model (Or one very like it) is used in the vast majority of
dive computers on the market. Even the Suunto RGBM algorithm which suggests
is a bubble model still works more like a traditional Haldanean model.
There are very few computers that use the VPM algorithm to work out 'live'
deco.

Regards
Jason
On Thu, Aug 28, 2014 at 3:47 PM, Guillaume Gardet <guillaume.gardet at free.fr>
wrote:

>
> Le 28/08/2014 16:38, Dirk Hohndel a écrit :
>
>> On Thu, Aug 28, 2014 at 04:30:31PM +0200, Guillaume Gardet wrote:
>>
>>> For Bühlmann there are multiple models :
>>> * number of tissue compartments (8, 12 or 16)
>>> * A/B/C variants (at least for ZHL-16): A is theoretical only, B is for
>>> tables generation and C is for dive computer (more conservative).
>>>
>>> So, we could implement those variants.
>>>
>> The biggest challenge here is "who would implement this".
>> We have learned that the discrete implementation of these models is rather
>> tricky (as a divelog we only get the samples at the sample rate the dive
>> computer returns to us). And because of that, even if we know exactly
>> which model a dive computer is designed to implement, we still usually
>> don't match the deco data the dive computer shows, as it has access to the
>> continuous depth information. Additionally many divecomputers have rather
>> under-powered CPUs (to say the least) and they are taking serious
>> shortcuts when calculating the compartment values - which also leads to
>> different results.
>>
>> Long story short: it's not clear to me if there is value in implementing
>> other variations of the Buhlmann algorithm - it's unlikely we'll ever
>> perfectly "match" any dive computer you are diving.
>>
>
> Sure we will never perfectly match logged dives, but my use case would be
> more in planning mode.
>
>
>> I'd be more interested in a VPM implementation (that is reasonably well
>> documented). We had a GSOC proposal to do just that and decided not to
>> accept it but it's still something that we are open to if there's a
>> developer with the necessary math / physics background willing to tackle
>> the problem.
>>
>
> Do you have pointers for implementing VPM? Willem wrote it was totally
> proprietary.
>
>
> Guillaume
>
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