Dive Planner: Inconsistent dive ceiling calculations

[Willem Ferguson]

On 02/01/2018 15:34, Robert Helling wrote:
> Willem,
>
> reading your second mail, I understand there are only two different 
> ceilings left: The one in the divelist which equals the one in the 
> planner when you remove the ascent points and the second one you get 
> in reedit until you remove the ascent waypoints.
>
> This is a „feature“ of the VPM-B model: It treats the „decompression 
> phase“ different from the bottom part of the dive, in particular it 
> takes note of the ceiling at the beginning of the decompression. In 
> the planner (as well as replan), we take all the explicitly listed 
> waypoints as the definition of „bottom phase“ (so in replan before 
> deleting the waypoints, the whole dive is „bottom phase“). In the 
> divelist we make a clever guess (thanks to Rick’s code) as to where 
> the bottom phase ends. This tends to be very close to the true bottom 
> phase of planned dives (when the entered waypoints end at the deepest 
> part of the dive and then the planner takes over and manages the 
> ascent) but is not exactly the same.
>
> I have recently blogged about this problem here
>
> https://thetheoreticaldiver.org/wordpress/index.php/2017/12/22/vpm-b-for-real-dives-or-not/
>
> Best
> Robert

Hi Robert,

It's such a pleasure interacting with someone who really understands 
this thing, because I do not. I will document this issue in the user 
manual. It's really the way that the representation in Subsurface 
interacts with the VPM algorithm when a dive plan is reloaded for editing.

Would there be a possibility of a user defining the end of the bottom 
section of the dive and for automatically clearing the ascent dive 
points when a plan is reloaded from the dive list for editing? I 
understand how arbitrary the "start of ascent" can be, e.g. when doing 
multi-level diving.

V-planner handles this problem in a bit of a different way. One can 
define predetermined segments (e.g. a multilevel dive or a cave dive) 
that cannot be avoided in the ascent. However, between these segments, 
V-Planner still calculates a deco schedule. For instance if a multilevel 
dive has two depths, e.g. 40m for 20 min; then 20m for 20 min, V-Planner 
still gives deco stops between 40m and 20m, even though there is a 
pre-determined 20min "stop" at 20m. It would be wonderful if Subsurface 
has a way of dealing with this situation. You have no idea how powerful 
the Subsurface dive planner is for rapid graphical assessment of gas 
volumes used, planning for possible failure of a deco cylinder and many 
other things. The graphical representation makes an enormous difference.

Thank you so much for your time.

Kind regards,

willem



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