Vyper Novo and NDL and Saturation level questions

[John Doe]

Hello,

I recently discovered this nice piece of linux software and I'm now using it to log all my dives.

I have a vyper novo and It could out of the box fetch the dive data.

So far, the temp, depth, time and some events/warnings are fine.

However, I thought I could also display or check the NDL on the graph? Either the NDL from the computer and/or NDL computed by subsurface.

Am I missing something?

Another feature I'm wondering is the level of nitrogen sursaturation after a dive? Is there a way to compute either the indice for some dive table (ie padi dive table indice E)?
Would be interesting to have a graph of de-saturation (just curious about how long it takes to completely de-saturate).

Best regards and thanks for this excellent opensource tool.

Laurent

[Jason Bramwell]

For your first point where you want Subsurface to show you no-deco time or once in deco how much time you have clocked up this is a feature you can have but you have to turn it on.

 

The button to enable this is here, this turns on NDL (no deco limit) and TTS (time to surface) information. The button just above this is interesting too and may help to so some way to answer your second point although this might not be what you were looking for:

 

Then once activated you’ll see additional lines in the small stats box like this (see pic). One of these NDL entries is reported by my dive computer and one of them is what Subsurface has calculated:

 

The extra info tab for my particular computer (OSTC Plus) shows additional info reported by my dive computer, this shows things like desaturation time but your computer may report things differently.

 

Sent from Mail for Windows 10

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[John Doe]

Hello JB2cool,

Thanks for your answer and clear explanations.
I only have the calc NDL, not the one from the computer. Also There are no other extra info (see below, I tried to activate all options).

Is it normal for this computer or some information are not decoded correctly?

I saw an option to save the exchanged data during sync and will see what it gives.

Best Regards,

[Robert C. Helling]

Am Dienstag, 28. Juli 2020 18:48:46 UTC+2 schrieb John Doe:

Another feature I'm wondering is the level of nitrogen sursaturation after a dive? Is there a way to compute either the indice for some dive table (ie padi dive table indice E)?
Would be interesting to have a graph of de-saturation (just curious about how long it takes to completely de-saturate).

Subsurface has in integrated dive planner. That takes into account residual nitrogen from the dives in the log (for it to properly work, you need to set date and time in the planner properly). This takes into account tissue saturation at a much more detailed level than a simple "repetition group E". 

[Linus Torvalds]

On Wed, Jul 29, 2020 at 1:00 AM John Doe <lbalt...@gmail.com> wrote:
>
> I only have the calc NDL, not the one from the computer.

Hmm. It looks like libdivecomputer really doesn't get NDL information
from the D9 family (which includes the Vyper Novo).

Jef? I see that the sample data has that "size" thing that
libdivecomputer ignores (well, it updates the offset with it, but it
doesn't say anything like "ok, if the depth sample type has 3 bytes,
the last byte is the NDL in minutes").

I'd be surprised if the NDL really isn't there at all, but maybe
Suunto decided they can just calculate it offline the same way the
dive computer does and they didn't bother.

We obviously can't recreate the dive computer NDL, since Suunto uses
its own "fancy" microbubble gradient thing.

Linus

[lbalt...@gmail.com]

Hello Linus,

Thanks for your attention (I can't believe I'm writing to you :D)

I have no idea if this info is present or not. I've attached the bin file generated during a dive import in case.
I could also try to install suunto software on my wife computer and see what info they get out of it...

I have no idea how the data with libdive computer is extracted. I mean if this information is not present, is it:

- because it's not there at all

- libdive doesn't extract it

- subsurface doesn't parse or import it from lib dive

Best regards,

Laurent

[Jef Driesen]

On 29/07/2020 20:07, Linus Torvalds wrote:
> On Wed, Jul 29, 2020 at 1:00 AM John Doe <lbalt...@gmail.com> wrote:
>>
>> I only have the calc NDL, not the one from the computer.
>
> Hmm. It looks like libdivecomputer really doesn't get NDL information
> from the D9 family (which includes the Vyper Novo).
>
> Jef? I see that the sample data has that "size" thing that
> libdivecomputer ignores (well, it updates the offset with it, but it
> doesn't say anything like "ok, if the depth sample type has 3 bytes,
> the last byte is the NDL in minutes").

I'm not sure what you mean here. Depth and pressure sample is always 2 bytes,
and temperature sample always 1 byte long. So there are no extra bytes present.
Those types are also the only existing sample types. If there would be another
sample type, parsing would fail. That's because we don't know it's size, and
hence can't skip it. The size isn't stored in the data itself, it's set in the code.

> I'd be surprised if the NDL really isn't there at all, but maybe
> Suunto decided they can just calculate it offline the same way the
> dive computer does and they didn't bother.

There are only the deco/ndl flags in the events, which we already translate to
the deco/ndl sample. But the more detailed information like ndl time or deco
stop time and depth simply isn't there. So those are set to zero. So we can only
tell the user the deco/ndl state, but without any time or depth information.

It looks like subsurface discards this info, because it relies on the stop depth
to set the in_deco state:

} else if (value.deco.type == DC_DECO_DECOSTOP ||
value.deco.type == DC_DECO_DEEPSTOP) {
sample->stopdepth.mm = stopdepth = lrint(value.deco.depth * 1000.0);
sample->stoptime.seconds = stoptime = value.deco.time;
sample->in_deco = in_deco = stopdepth > 0;

I'm not sure how to visualize this on the graph without a depth, but that's
another issue.

Jef