Tuesday, August 29, 2006

GeoTagging: Image + GPS Data

Back from Tuolomne along Hwy 120 you start to mess again with the EXIF 2.2 standard spec to understand a bit better the metadata that viewers like Exif Reader, Exif Tool, FastStone give us.

EXIF (Exchangeable image file format for digital still cameras) defines a header to a JPEG image file. The point here is that EXIF tags support GPS data, so you can associate corresponding latitude, longitude and altitude values of a location to a picture. In fact, you can associate a ton of info from a GPS receiver: bearing, distance to target, there are at least 30 fields for GPS related data only.

As covered at a previous post cameras that generate EXIF headers with their associated GPS Receiver data don't come cheap or easy. And if you want to get dirty and code something yourself check Exiv2, a C++ library for EXIF handling.

A workaround requires a way to associate which picture you took at which position. With a GPX log file from a receiver and time of the day you can batch read a series of JPEG files and rewrite them with the corresponding location information. [Check a most recent post for an actual implementation of this idea].

Tools

GPS Photo Linker from GeoSpatial Experts (don't confuse with the freeware below) iTag and GeoSnapper were covered in the same post about GPS Cameras.

This time Mac users are in luck. The freebie GPSPhotoLinker seems to be well appreciated. Windows users have a professional and efficient choice with RoboGeo. These products will solve questions like: How to upload GPX tracks? Or associate a specific picture to a location from that track?

For iPhoto users, check the iPhotoToGoogleEarth plug-in.


Showing off

But then, where do I put these pictures? Which sites take geotagged photos? Here the choice seem to go around Flickr, Zoomr, loc.alize.us, Fotki, YourMap, Yuan.CC Maps and Panoramio.

RoboGeo for example, can export geotagged photos to Flickr, after you go through its authorization process that will only require your account name (if you are already logged into it). Then at Flickr you can associate those pictures to a map. You can then search the map for pictures titles. Flickr will also let you post uploaded photos to a blog, even through email. Things are moving fast on this lane.

At the end, the photos got geotagged and uploaded but location was off. Not sure where in the process the units weren't respected. The values displayed by Flickr didn't match the original ones provided to RoboGeo. There is also a XML GeoTag that can be generated by tools like RoboGeo or generated from the EXIF data, but that's an extra step or workaround.

I might have switched the pictures but something tells me that the location data based on the original EXIF information still requires some work at Flickr, but I might be wrong here.

Pointers

FlikrFly has a Google Earth connection. More about Flickr on this /. thread and also scilib, txfx, flickr and thomashawk. Special attention to Thomas Hawk. Check also Geobloggers.

Lots of resources on GeoTagging at Richard Akerman's Geocoding Photos.

See Also: "Geolocation through IP" at the Linux Journal. Pay special attention to the comments. And this post.

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