wiki:Help/AudioMapping/GPSWaypoints

Audio Mapping: Continuous audio with GPS waymarks

This method of audio mapping uses waypoints collected using your GPS to identify the position of a feature and a continuous audio recording to take notes. Synchronization and calibration of the sound track provide a convenient means to play back the notes for each waypoint, but aren't critical to the geography of the map.

Procedure:

Before you start

  1. Consider calibrating your voice recorder.

While surveying

  1. Start your voice recorder and obtain a fix with your GPS.
    • It is just a little easier to synchronize if you start the voice recorder first.

  1. Once you have a fix, you might want to start moving just to make sure your location is clear.
  1. Simultaneously add a waypoint to the GPS and add an audio cue to the sound track, for example "synchronization cue: Three, two, one, NOW!".
  1. Do your surveying. Whenever you want to dictate notes, make a waypoint on your GPS just before you speak. For points of interest, be sure the waypoint will indicate its location; for street names you just need to be sure there won't be any ambiguity in the position.
    • If your GPS doesn't allocate a number to the waypoint automatically, consider giving it a name.
    • Ideally, dictate the waypoint name/number before describing it: "point 32: C of E Church, St Luke's, on left set back 30m from the road". Not essential, but it just confirms you are where you think you are when playing it back.
  1. If you want to make a pause during your survey and switch off the GPS, keep the voice recorder running if possible. This will make synchronization in JOSM much easier.

On the computer

  1. Extract your tracks from the GPS as a GPX file, and your sound track from the recorder as a WAV file.
    • JOSM (actually, Java's built-in audio facilities) doesn't recognise every variety of WAV file encodings. If you need to (JOSM will tell you), convert your recording to a suitable format using e.g. Audacity. 8,000 16-bit samples per second is a reasonable format.
  1. Open your GPX file. This will create a GPX layer showing the track.
    • if you have explicit waypoints in your GPX file you will also probably see a Marker Layer for those waypoints. You will most likely want to turn this behaviour off by un-checking 'Create non-audio markers when reading GPX' in Audio Preferences.
  1. Import your audio file using Import Audio on the GPX layer's context menu. After you identify your WAV file you should see a Marker Layer with audio markers for your waypoints.
    • if you don't see the markers you expect, for example you get only one called 'start', you may need to change what markers are created in the 'When importing audio, make markers from...' section in Audio Preferences:
      1. you may have 'Explicit waypoints with valid timestamps' turned off.
      2. your waypoints may not have timestamps or they may be stamped only with the date, not the time, in which case choose the estimated time option rather than the explicit waypoint option. (Garmin devices typically don't usefully timestamp waypoints).
      3. it is possible your GPS represents your marks by giving names/numbers to particular points on the track rather than separate waypoints. JOSM will recognize these while importing audio if you turn on the 'Named trackpoints' option.
    • If you don't see your names or numbers along with the Audio Marker icons, check that the 'Label audio markers' option in Audio Preferences is on.
  1. Synchronize your sound track to the GPS data. There are two ways of doing this.
  1. Play each Marker and create the streets and features you described at the locations indicated by the Marker, in the usual way.
    • If you start finding gaps in play back before you hear what you expect, or audio starts part way into your comment:
      1. you may not have calibrated correctly
      2. you may have been speaking too soon or too late while mapping: you can insert a lead-in time to compensate for this using 'Lead-in time' in Audio Preferences.
      3. you may need to re-synchronize (as per 4 above) on a later marker (perhaps you paused while making the recording). Re-synchronization only affects later markers, so earlier ones will not change.

You can also use the audio controls to pause, play back etc. and you can drag the orange play head marker around to jump to a particular point in the recording.


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Last modified 9 years ago Last modified on 2010-05-12T04:54:37+02:00