Pro Plus 2

[Jef Driesen]

On 01/14/2012 07:57 PM, Philip Balister wrote:
> On 01/14/2012 01:25 AM, Jef Driesen wrote:
>> On 01/13/2012 11:04 PM, Philip Balister wrote:
>>> 1) I have six dives in the computer, but only the first 5 show in
>>> subsurface.
>>
>> Depending on your (short) sample rate setting and (long) dive times,
>> it's possible there is not enough memory to store profiles for all
>> dives. In addition to the profile data, the oceanic dive computers
>> maintain a summary for each dive stored in separate memory area. So it's
>> possible the dive computer can show dives for which it doesn't have the
>> profile data anymore.
>
> Sample rate looks like 15 seconds. It is the most recent dive that does
> not show up.

I already found where it goes wrong. The dive is downloaded correctly, but the 
parsing fails, and I guess subsurface doesn't import anything at all in that case.

The problem is that the vtpro compatible dive computers support a depth based 
sample rate in addition to the time based sample rate. This means the dive 
computer doesn't record at fixed time intervals, but whenever a change in depth 
crosses a certain threshold. To be able to draw the profile graph, a timestamp 
is recorded for each sample. This "feature" is a real pain in the ass because it 
does break any application that assumes a fixed time interval between two 
samples. To make things even worse, the timestamp only has a resolution of one 
minute, which means there can be several samples with the same timestamp. 
Another potential problem because applications are likely to expect the 
timestamps to be unique and increasing for each sample. To workaround this 
issue, the libdivecomputer code counts the number of samples within the same 
minute, and then spread them evenly.

It's this timestamp that is causing the trouble in your case. Normally with a 
time based sample rate, there is a fixed number of samples per time unit. For 
example a 15s samplerate will always have 4 samples per minute. But that 
assumption is violated in your problematic dive. There are 5 samples with a 
timestamp of 37 minutes. I have absolutely no idea why the dive computer does 
this. It's the first time I encounter this.

Jef