Silly problem with dive sites and GPS downloading

Monty Taylor mordred at
Mon Sep 24 09:42:27 PDT 2018

On 09/24/2018 11:04 AM, Dirk Hohndel wrote:
> 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.

Maybe also an option somewhere, for when the GPS data logger is being 
used in the Android app, to save all of the collected GPS points as text 
records onto the dive object as well when applying GPS data. (at least 
the ones between start and end times of the dive)

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

Let me see if I can make it even more complicated - because I'm pretty 
sure more input will definitely make this clearer.

A few of the other loggers, at least diviac and, split the 
location of a dive into two ideas "Location" and "Dive Site". (neither 
particularly explain the difference spectacularly) The way I've come to 
understand the split is that Location is "the real geographical place 
where I set up my gear" and Dive Site is "the place where I was under 
water". Now with Mk1 GPS or other sets of coordinates, each dive also 
potentially has a specific "path" - that is a path described across a 
dive site.

Specific examples, to attach concrete examples to abstract concepts:

Blue Hole, NM:,-104.6819938,15z/data=!3m1!4b1!4m5!3m4!1s0x871c0b5ae1b0dfe9:0xe7228c5b0ba0698a!8m2!3d34.940447!4d-104.673239

Scuba Ranch, TX:,-96.1552064,17z/data=!3m1!4b1!4m5!3m4!1s0x86495b7f045849e7:0x7e45bec3eb6d9080!8m2!3d32.7891403!4d-96.1530177

Flynn Reef, Australia:,146.2558661,14z/data=!3m1!4b1!4m5!3m4!1s0x6979cbf27dcbb67d:0x778f3f250b640676!8m2!3d-16.7243701!4d146.2733758

Blue Hole, Scuba Ranch and Flynn Reef are all Locations.

Blue Hole has one eponymously named dive site and is super easy. There's 
also only one entry/exit point. It's a hole.

Scuba Ranch is also just one "Location" - there is an entrance where you 
pay a fee and where you can get your log stamped. There are maybe 10 
different parking lots/shore entries (not sure the distinction matters, 
but maybe it does?) - and in general different local groups have "their" 
spot where they always dive from. Inside the flooded quarry there are 
several "Dive Site"s - there's a sunken airplane, two boats, a big metal 
fish and several dive platforms. If you dive there a bunch, maybe 
because you're a local, which dive you did might be more interesting 
than just "Scuba Ranch" - but also you're certainly at Scuba Ranch for 
all of them.

Flynn Reef is a real geographic place with a real name, but being a reef 
there are more than one spot on it where your boat might moor. From any 
one of those moorings, there are multiple available "Dive Site"s ... and 
I'm pretty sure the different dive operators call at least some of them 
by different names.

Throwing the Linus Mk1 GPS start/end tracking in to the mix, and now 
there are also the possibility of one or more distinct "Dive"s with 
locations at a given "Dive Site".

Flynn Reef has GPS coordinates, it's a place. Nemo's Bommie also 
probably has GPS coordinates - or more to the point is at least a 
logical place where saying "these 4 dives were all at Nemo's Bommie" 
makes sense as a human. Then each dive at that dive site has the 
potential to also have specific GPS start/end coordinates, even though 
the dive might be associated with a Dive Site and that Dive Site might 
be associated with a Location.

As you go from General to Specific, the GPS information becomes less 
likely to be shareable with others. I can _definitely_ tell you about 
Blue Hole, NM, Scuba Ranch or Flynn Reef and you can _definitely_ go to 
those places - and there isn't any dispute that they are places. The 
Dive Sites at those places are also potentially interesting- but are 
also up to interpretation in terms of what, if anything, to call them. 
The specific Dive GPS coordinates are almost never interesting to 
someone else, but still *might* be in case you're trying to tell someone 
about a cool drift dive you did - and communicating "I went in at the 
beach north of the Maui Sheraton then did a (slow) drift around Black 
Rock and exited south of it" is maybe useful to track/communicate.

Sorry, that's a giant pile of words.

What I'd personally love to be able to do is arrive at a "Location", 
pick up my phone/computer and say "I'm at a new Location called Flynn 
Reef" or "I'm back at existing Location Flynn Reef". Then, as the 
divemaster is giving the briefing (or if I'm giving myself the briefing) 
I could pick up my phone and Add a new Dive Site called "Nemo's Bommie". 
I could mark it as being at the Location Flynn Reef. I might want to 
attach a map of the dive site to the Dive Site - and that map would be 
relevant to any dives done there.

When I'm done with the dive, I import the dive and I could then select 
"Nemo's Bommie" from the Dive Site list. If the dive came with its own 
start/end GPS coordinates - or if I drift dove pulling a tender 
overhead, maybe I left my phone with the GPS tracker running in the 
tender so I've actually got a decent-ish path even. Maybe soon one of us 
will get a and

That's super complex - and it's possible people might not want to manage 
3 different objects of informatoin each with 1:Many relationships. So if 
we got more complex modelling of locations, it's probably important for 
a human to be able to just dive, and say "I dove at this place" and not 
care about having Location->DiveSite->Dive.

In some ways - it might be more accurate to consider Location and 
DiveSite to both be areas rather than points. For instance, Flynn Reef 
is actually a whole reef. Then, inside of that Area, there are multiple 
Dive Sites, each of which being an area underwater that could be 
described with a map. And then dives are paths on top of that under 
water area.

In that sense, a Location is an area that is (or could be) a mappable 
area by Google Maps. A Dive Site is an area under water, and a Dive is a 
path. The simple cases are then that a given Location and Dive Site and 
Dive are the same, and are a zero-dimensional area described by a single 
GPS coordinate.

Or maybe that's WAY too much.

>> On Sep 24, 2018, at 8:26 AM, Linus Torvalds <torvalds at> wrote:
>> On Mon, Sep 24, 2018 at 6:12 AM Monty Taylor <mordred at> 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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