[josm-dev] Question about audio file mapping/synchronization

[David Earl]

Hi,

I'm the original author of the audio code. I've had a look at what's 
there now, and the GPX reading code has changed quite a lot since I 
looked at it, but it seems to me like it is not associating links with 
trackpoints any more. But also trackpoints and waypoints are handled by 
the same piece of code, so I'm rather puzzled that a link element would 
work on one and not the other. I'd have to go in with a debugger to be 
sure what's happening as I can't really follow my way round the code any 
more without refamiliarising myself as it has changed so much.

Anyway, as you say, that's all rather unnecessary. Providing the 
"Modified times of audio files" preference is on, when you Import Audio 
by right clicking on a GPX layer you can select multiple files and it 
will put audio buttons at the times for each clip selected.

Note that it uses the *modified* times of the files and these are 
assumed to be the time at the end of the recording (because that is 
presumably the last time the file was modified, for obvious reasons), 
though the button is displayed in the GPX track at the start of the 
recording.

Regarding time zones, if the GPX doesn't explicitly say its times are in 
some time zone it appears to assume UTC (which is what the GPX spec 
says; though strictly speaking it is invalid GPX without the explicit 
'Z' in the ISO format date, but as lots of GPS units and software doen't 
put the 'Z' in, it is sensible to assume it).

For file time stamps it shouldn't matter about time zone, as the time 
stamp is stored in UTC in the operating system and time zone of the 
machine is only used to display times, e.g. in a file properties dialog.

However, if you are using a recorder which doesn't understand time zones 
at all, then you'd have to adjust for this before import to JOSM. But I 
imagine this would be obvious as the times of the files would show up 
wrongly in File Properties too, for the same reason JOSM would get it wrong.

David

On 23/10/2010 22:08, activityworkshop wrote:
> Hi all,
>
> First of all, thanks for JOSM, it's a great tool for contributing to OSM.
>
> I have a few questions regarding the audio functionality of JOSM and the
> various ways it can be used. I got these questions because I'm the
> author of the "Prune" tool which is used by some people to prepare their
> GPS tracks before importing into JOSM.
>
> Prune can already figure out the locations of photos using their
> timestamps and a corresponding gps track, and I received the following
> feature request for Prune to do the same for audio files:
> http://sourceforge.net/projects/prune-gps/forums/forum/682167/topic/3746079
>
> I've now got the basics working (although it's not released yet), but I
> wanted to run things past you josm-devs first. I noticed that if the
> points attached to the audio files are track points, JOSM seems to
> ignore the audio information. If I convert them to waypoints in Prune
> and then re-export the gpx file, then JOSM shows the audio files
> properly. So my first question is, is this intentional behaviour that
> only audio files connected to waypoints are recognised? Is this likely
> to change in the future? It's awkward for me because when Prune
> associates the audio file with a point, it's almost 100% certain going
> to be a track point (ie, a point without a name). Converting all the
> audio points into waypoints is then a pain.
>
> While looking around JOSM's help files, it then strikes me that you
> josm-devs have already done a lot of work on this audio synchronization
> problem, and maybe all this audio stuff doesn't even need to be in Prune
> at all. If you can do all this in JOSM already, then there's no reason
> to do the same in Prune only to load the files into JOSM anyway. What do
> you think?
>
> Unfortunately I wasn't able to figure out how to properly synchronize my
> audio files within JOSM, because I couldn't work out how to apply my
> timezone offset (GPS track in UTC, audio files in local time). Is this a
> feature that's planned, or is the idea to always reset the audio
> recorder (or camera) clock to UTC?
>
> I'd be very interested to hear your thoughts on this!
>
>
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