Quirks of the Subsurface dive planner

[Robert Helling]

Willem,

just a quick reply (before work, I mean paid work):

Thank you so much for all these remarks, this is extremely helpful!!!

> On 30.01.2017, at 07:44, Willem Ferguson <willemferguson at zoology.up.ac.za> wrote:
> 
> Robert,
> 
> Thank you very much for your feedback on this issue and for the associated patches you submitted. Apologies for a long reply. During the last week I have been using the planner quite intensively. The reason is mainly twofold: the graphical interface that allows a visual confirmation that the dive plan is set up as intended, including partial gas pressures; 2) the facility to check expected gas pressures at critical points along the planned profile: this is of enormous value for gas management during the dive. Below are a few comments on the behaviour of the planner that I think need attention.
> 
> The types of dives that we planned involved the use of a travel gas in trimix dives of a cave system. therefore a large part of the profile after the deepest point of the dive are specified in the dive points table (therefore differing from an open-water dive where the planner deals with the total ascent from the end of the bottom section of the dive to the surface). The strategy was to initiate the dive with nitrox, switch to trimix as a main back gas for the deeper part of the dive, then switch back to nitrox upon getting back to shallower levels and with final deco using oxygen. In short, there are two problems: 1) The order in which the gases are entered in the cylinder table has an effect on the rendering of the data; 2) when saving a plan and re-opening and editing it in the dive planner, the gas changes are forgotten. Below are some images of a stereotyped dive plan using the above approach.
> 
> Case 1: Here the order in which the cylinders were defined are: nitrox, trimix, oxygen. Image Case1a indicates a plan after saving it and viewing it from the dive list. Looks ok, no problems. Image Case1b shows the same dive after opening it again for editing in the dive planner. The second gas change has been forgotten, requiring extensive editing of the Dive Points table.
> 
> Case 2: Here the order in which the cylinders were defined are: trimix, nitrox, oxygen. Many divers would reason to use this order because the trimix is the main back gas, the other cylinders being ancillary. Here there are problems arising from the fact that the first cylinder defined was trimix, but the dive started with nitrox. The points to be seen in image Case2a is that
> 
> (i) the cylinder pressure graphs for nitrox are not shown on the planning screen. The gas pressure calculations are, however done, evident from the final gas pressure for nitrox actually being shown.
> 
> (ii) Also, notice on the left margin of the profile (near the 20m depth tick mark) that there are two cylinder labels: trimix as well as nitrox. I assume what happens is that, since the trimix cylinder was the first one defined in the cylinder table, the planner assumes that the dive begins with trimix. Then, when in the dive points table, the first segment is in nitrox, the planner inserts a gas change event from trimix to nitrox right at the start of the dive. It would be wonderful if the profile could automatically start off with the first gas defined in the dive points table and not with the first cylinder defined in the cylinder definition table. I realise that this issue is probably difficult to deal with because of the integration between the planner profile display and the "normal" dive log display where the cylinder definition table is filled in the order in which the dive computer provides the cylinder gas data after the dive. But the usability of the planner interface would really be much more user-friendly if the profile display is not dependent on the order of the cylinder definitions.
> 
> Image Case2b shows the profile after being saved, and viewed from the dive list. Pretty much as it looked on the dive planning screen. Still no gas pressure graphs for nitrox.
> 
> Image Case2c shows the same dive plan after re-opening it for editing in the planner. In this case, both gas changes involving trimix has been forgotten, again requiring extensive re-editing of the dive points table.

I will have to look into this with more time. Please keep nudging me until this is resolved. Besides the screen shot, it would make analyzing this a lot easier if you could include an xml with the dives as well.

> 
> There are some smaller issues that relate to the ease of use of the planner:
> 
> i) If I change the gas in the dive points table, it would be very useful if all segments below the one being edited were also changed to the same gas. For instance, if I change the gas in the 3rd row of the table to EAN40, it would be helpful if all the rows underneath were also changed to EAN40. This way I do not have to change by hand each of the subsequent segments to EAN40. I realise that, if final deco is done with oxygen, these will also be overwritten with EAN40, but that would require only one re-edit of a row lower down in the dive points table, changing the gas to oxygen: then all the rows underneath would also be changed to oxygen. I think the fundamental reason for such a request is that the dive points table for these sorts of dive plans includes quite a long list of explicitly-defines dive points.

This is (at least semi-) intentional. You get the behavior you want by right clicking on the waypoint in the profile and inserting a gas change. I always thought this is the expected behavior: In the table you change a single leg of the dive, as this is what a row corresponds to, in the profile you insert a gas change that stays valid until the next explicit gas change. One might think about allowing several rows of the table to be selected simultaneously and then editing one affecting all selected. Let’s see if we can do that.

> 
> ii) It would be invaluable if it were possible to insert a row in the dive points table. Let's say I planned a dive, and in one of the dive segments I want to add another depth level during the descent (or ascent). Currently I can do that by double-clicking the profile and creating a new dive point. But a) this operation does not always have a predictable effect and b) now I am dependent on interaction with the dive profile panel for doing changes to the dive points table. Our approach in the past (I think) has always been that editing the dive points table is the better way to put together the segments for display in the profile panel.

I second Rick’s answer here. What would be the expected behavior: The same as double click in the profile (i.e. subdivide the previous leg) or actually insert a leg (i.e. shift all the following segments to a later time)?

> 
> iii) When re-opening a dive plan for editing in the planner, the final part of the dive plan (determined by the planner) is hard-coded into explicit dive points represented in the dive points table. This has some very nasty consequences. For instance, if I reposition a gas change along the profile using the profile panel, gas changes later on in the plan are often screwed. In many cases, the change to oxygen is moved to the very last segment of the dive plan: clearly erroneous. This means I have to delete all the dive points from the end back towards the point where I exit the cave into open water and let the planner recalculate the final deco again.

The gas changes should not be screwed. As I said before: There is (at least currently) no way in our file format to record the distinction between manually entered points and computed points. Whenever we go through a file on disk, the whole profile is considered manually entered. That is a problem of the file format.

> 
> iv) When re-opening a dive plan for re-editing the plan in the planner, a zero-time dive point is still inserted as the very first dive point.

Hmm.

> 
> Please do not take these remarks as criticism of any sort. One could argue that the way that I use the planner here is a corner case. My motivation for adding improvements to the planner is twofold: 1) I place very large value on the Subsurface planner because it has unique advantages; 2) robustness of the planner is an important part of making this software a prime choice for other divers.
> 

Thanks again
Robert

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Robert C. Helling     Elite Master Course Theoretical and Mathematical Physics
                      Scientific Coordinator
                      Ludwig Maximilians Universitaet Muenchen, Dept. Physik
                      Phone: +49 89 2180-4523  Theresienstr. 39, rm. B339
                      http://www.atdotde.de

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