[OSM-dev] Fwd: Mobile Phone Audio Mapping Tool?

[David Earl]

OK, I think from a quick scan you need <link href='uri'/> in a waypt or 
trkpt element where uri is e.g. "file:://pathname.wav" (which I think 
can be relative).

If you can I'd add a waypoint or trackpoint at the time you press the 
button, rather than adding it to the most recent trackpoint. You could 
also auto-number the points so the labels show up in JOSM (trackpoints 
can be selectively and explicitly named so you don't need separate 
waypoints)

But I wonder whether it is worth it. Unless you are going to go deeply 
into the phone's track recording mechanism, you're going to be trying to 
postprocess the track to introduce <link> elements, when just getting 
the timestamps right is easier. In either case you still need to at 
least check the calibration. Only if you can get a button on the phone 
to simultaneously introduce a waypoint with a link and start the 
recorder at exactly the same time are you going to avoid this. I can't 
help feeling you're making work for yourself (though it may be the 
challenge that's interesting you).

Calibration is a one off thing and synchronisation is a matter of 
seconds to do when loading a track. I think getting the timestamps right 
is likely to be a lot easier than changing the way the GPX file is 
generated; and recording a continuous track is easier still (though your 
phone may limit the length of the recording in which case you have 
little choice).

David


On 28/03/2009 10:13, Graham Jones (Physics) wrote:
> David,
> Thanks for the comprehensive reply!
> 
> My idea is similar to your option (b).  What I envisage doing is 
> pressing a button on the phone which then records an audio clip, and 
> associates the GPS location with that clip.  These will be saved on the 
> phone's memory.
> It will then be necessary to export the clips and locations to JOSM - 
> the simplest answer sounds like the use of a GPX file with references to 
> the audio clips - it will effectively be like setting a waypoint on a 
> Garmin GPS device, but without the trouble of trying to type in the name 
> with the silly little joystick while avoiding traffic....  Therefore if 
> you could point me to what the <link> specification needs to be for 
> JOSM, that would be very useful please.
> 
> The phone creates the clips in 'amr' format, but it shouldn't be 
> difficult to post-process these into WAV, either as a separate 
> application or as part of a JOSM plugin.  I'll not try to do that on the 
> phone just yet.
> 
> I'll try to get the storage bit working, then should be able to publish 
> something for people to try....
> 
> 
> Graham.
> 
> 2009/3/27 David Earl <david at frankieandshadow.com 
> <mailto:david at frankieandshadow.com>>
> 
>     On 27/03/2009 21:21, Graham Jones (Physics) wrote:
> 
>         I am after a simple way of recording street names when cycling
>         rather than having to write them down.  There is a section on
>         the Wiki on "Audio Mapping", but there is no mention of using a
>         normal mobile phone and bluetooth GPS receiver - the idea is to
>         record audio clips and associated location to import into JOSM
>         later.  The advantage of a phone over the other methods is that
>         it should be able to record both audio, and GPS location at the
>         same time, to avoid the synchronisation problems.  It is also
>         nice and small, and you don't look odd talking into one.   It
>         might even be possible to use a bluetooth headset which would be
>         even easier for cycling...
> 
>         I have had a bit of a play and I think I can make it work (the
>         GPS receiver can talk to the phone, and the phone can record
>         sounds), but I haven't stitched it together in to a single
>         application yet. I can't help but think that someone will have
>         tried this before (and presumably failed because I can't find it
>         anywhere?) - does anyone know if I am onto a loser before I go
>         too far down the road of coding it?  There is a bit more
>         information at
>         http://wiki.openstreetmap.org/wiki/Talk:Audio_mapping#Mobile_Phone_Version.3F
> 
>         Any pointers to where this is going to go wrong would be
>         appreciated!
> 
> 
>     Hi Graham,
> 
>     I wrote the audio bits in JOSM, so I can tell you what goes on at
>     that end, and I also added a new bit recently to support something
>     similar to this (so make sure you have a JOSM from the last couple
>     of weeks - I'd have to check for the exact build number).
>     Incidentally, the help in JOSM is more comprehensive than the help
>     OSM wiki page.
> 
>     However, a word of caution: the fact they are on the same device
>     doesn't necessarily mean you can dispense with sync or calibration.
>     It is quite likely the GPS track will generate its time stamps from
>     the GPS satellite time and the audio manage its sampling and time
>     stamps from the clock on the phone. They may not correspond exactly
>     (indeed you probably have to set the one on the phone explicitly)
>     and may drift a small amount. I think you should check this first.
>     You may be lucky, but don't take it for granted. An error of only
>     second or two can make quite a big difference and even if you can
>     set the phone clock to the same as the GPS a drift of only 0.1% can
>     make 100m difference on a long continuous recording.
> 
>     How to proceed depends on whether you're recording a continuous
>     sound track or a set of snippets.
> 
>     In all cases you need WAV files. If your phone records another
>     format you'll need to convert them to WAV (e.g. using Audacity).
> 
>     If many, short files then there are two approaches
> 
>     (a) have a set of WAV files whose (modified) time stamps are those
>     of the original recordings (i.e. if you converted them, you'll need
>     to use touch to bring the timestamps into sync with the original files).
> 
>     Tick the appropriate box in the audio preferences to say this is how
>     you want to work.
> 
>     Then when you import audio for a track choose _all_ the files (using
>     shift and ctrl click as appropriate in the file chooser dialog).
>     That will associate the audio clips at those time points along the
>     track. NOTE: the time stamps are those at the *end* of each
>     recording (for obvious reasons, I hope), but JOSM will take this
>     into account, so the point identified on the track will be at the
>     *beginning* of the recording.
> 
>     (b) postprocess the GPX file to add <link> elements to the relevant
>     trackpoints to refer to audio files. This is a manual equivalent of
>     the above. If you want to try this, let me know and I'll look up the
>     exact spec of the <link> tag for you.
> 
>     For a continuous recording, you would still need to sync, because it
>     is unlikely your track and recording will start at the same moment.
>     However, if you start the recording at the same moment you make a
>     waypoint, you won't need to record anything to mark the sync, it
>     will just be precisely the beginning of the recording, so you can
>     just briefly start playing and then immediately stop the audio from
>     the first waymark and sync. (Actually that's true anyway, you could
>     do this on any recorder).
> 
>     HTH
> 
>     David
> 
> 
> 
> 
> -- 
> Dr. Graham Jones
> Hartlepool, UK
> email: grahamjones139 at gmail.com <mailto:grahamjones139 at gmail.com>