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ImageIngester User’s Manual
Version 3.2, Update 1
Page 36
GPS Tagging
About GPS Tagging
GPS tagging means writing GPS coordinates—latitude, longitude, and altitude—into
ingested image files. Applications, such as Preview on Mac OS X 10.5 (Leopard) and
Lightroom, and web sites, such as Flickr and SmugMug, can read the coordinates and
associate the photo with a map location. With Lightroom, if you click the small right
arrow next to the coordinates, your web browser is opened to that location on a
Google Map:
II gets the coordinates for an image by reading a track log (containing coordinates
and times) written by a GPS device when the photo was taken and then interpolating
between the times using the photo’s EXIF date/time to find the coordinates.
For example, suppose the track log contains these coordinates (along with dozens or
hundreds of others):
<trkpt lat="40.085725375" lon="-105.588521529">
<ele>3240.260742</ele>
<time>2007-09-01T20:28:35Z</time>
</trkpt>
<trkpt lat="40.085720262" lon="-105.588498395">
<ele>3240.741699</ele>
<time>2007-09-01T20:29:19Z</time>
</trkpt>
<trkpt lat="40.085707856" lon="-105.588466460">
<ele>3241.222168</ele>
<time>2007-09-01T20:29:58Z</time>
</trkpt>
<trkpt lat="40.085716574" lon="-105.588510381">
<ele>3241.702637</ele>
<time>2007-09-01T20:30:51Z</time>
</trkpt>
Suppose then that you’ve taken an image on Sept. 1 at 20:29:27 (UTC or GMT).
There isn’t a track point for exactly 20:29:27, but interpolating between the 2nd and
3rd track points listed gives a position of 40.085718 latitude and -105.588492
longitude. Looking that up on Google Maps shows that the photo was taken in the
Indian Peaks area, just west of Boulder:
© 2007,2008 Marc Rochkind. All rights reserved.
2008-08-12