Silly problem with dive sites and GPS downloading

[Dirk Hohndel]

So Linus said some interesting things about this topic - and others
have added in the past. I'd like to try and connect some of the dots
here - please correct me if I get things wrong...

(a) a dive site, as an independent entity from a dive, does have a 
logical GPS location. One can argue where that is and in many ways
that's a matter of taste and opinion (e.g., is it where you enter the water,
or is it where the "interesting" part of the dive happens), but in general
a dive site has just one coordinate.

(b) a dive itself can be described in multiple ways. 
(1) Simply by the coordinates of the site. 
(2) by the entry and exit point.
(3) by the path that the diver actually took (turning the whole dive profile 
into a 3D path).

Today we do (b)(1).
It seems that at least with the Garmin we could relatively easily (assuming
the diver does turn on dive mode early enough to get a GPS fix before
being under water) do (b)(2)
I don't think there is equipment that is widely available to do (b)(3)

Typically when it's hard to foresee how things will get abstracted out
int the future, I tend to suggest using text fields / strings. Right now we
store all available GPS information on the Garmin as strings. Maybe
we should allow people to do this for other dive computers as well,
assuming they have a source for the strings (and we can of course use
the GPS info from a phone). Which means we'd need a way to do this
dive computer independently.

I'd love to hear people's thoughts on this.

/D

> On Sep 24, 2018, at 8:26 AM, Linus Torvalds <torvalds at linux-foundation.org> wrote:
> 
> On Mon, Sep 24, 2018 at 6:12 AM Monty Taylor <mordred at inaugust.com> wrote:
>> 
>> Maybe at least collect the start/end GPS so we have them in the data,
>> and maybe later someone will good idea for visualization?
> 
> For the Garmin Descent, the way it's currently done is that start/end
> coordinates are captures as "extra data" strings, with a key of GPS1
> and GPS2 respectively.
> 
> End result: the data does get saved, but only the last coordinate is
> then used for the dive site.
> 
> So I agree, there's no huge hurry about this.
> 
> Looking at the actual data I do have, it does seem to be (a) more than
> precise enough to warrant showing on the map and (b) not useful as a
> _path_.
> 
> For example, I did Blackrock in Maui as a "drift" dive (ok, so it took
> an hour and a half to "drift" a few hundred meters because there was
> no real current), and for that dive I got
> 
>  keyvalue "GPS1" "20.928930, -156.695058"
>  keyvalue "GPS2" "20.926903, -156.696113"
> 
> which if you look at a map looks exactly right, but if you draw a line
> between them it will go straight through the Sheraton Maui, because
> obviously the actual dive is *around* the rock.
> 
> So I think Dirk's argument that we don't have good enough GPS location
> is wrong - but it is true that it might be hard to show them sanely.
> 
> I think the Garmin Connect app showed the locations as a red and a
> green marker. I'm not sure that's great either.
> 
>                Linus
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