Share your geo-referenced images with the web-wide world in various forms.
Once, with some help from [Hack #10], you've gotten the hang of producing georeferenced photos, you'll want to take the next step by publishing them to your web site or to other collaborative photo services. As the geo-photo community has grown, so has the list of ways to publish your photos for others to see.
GeoSnapper (http://geosnapper.com/) and WWMX (http://wwmx.org/) are both services that try to ease the GPS-linking problem by providing tools to process your raw tracklog and photos. WWMX is a Microsoft product and works really well, but is based on the .NET framework, so it will only run on modern Windows operating systems. GeoSnapper works as a web service, and it will work for you as long as you have your tracklogs downloaded to your computer as Garmin MapSource or MacGPS Pro formats. [Hack #51] discusses GPSBabel, an excellent free cross-platform program that will simplify downloading tracks from your GPS and converting them between different common formats. It comes highly recommended!
http://locative.us/photomap/ holds the two Perl scripts that we wrote to produce photo maps and publish spatial metadata about photographs on the Web. The process happens in two parts. First, we create an RDF feed of metadata that describes the images and tags them with place and timestamps. Second, we use the RDF feed to plot the photographs over a base-map layer. Visit http://locative.us/photomap/ to download the two scripts, one named geoloc_media.pl and the other plot_rdf.pl. To run them, you need to have several Perl modules installed from the CPAN code archive: Geo::Track::Log, SVG, Image::EXIF, XML::Simple and RDF::Simple. [Hack #97] offers detailed instructions on the easy process of downloading and installing Perl code from CPAN. If you've been working through the hacks in this book, you'll have most of these modules installed already.
9.5.1. Create an RDF Feed of Photo Metadata
The first Perl script, geoloc_media.pl, takes a set of images and a GPS track in GPX format and spits out an RDF description of the images, annotated with time and place stamps and the creator's details.
This script assumes that you have a directory full of images that were taken while recording a tracklog with your GPS. You need to provide an address where that directory is available on the Web; this helps to uniquely identify different pictures and allows others to make descriptions of them.
The script needs to be run with several parameters:
perl geoloc_media.pl ...
Here's a sample run of the geoloc_media.pl script:
http://frot.org/20041020/ 20041020.gpx firstname.lastname@example.org /www/frot.org/20041020/* > photos.rdf
The end of this sequence, > photos.rdf, sends the output of the script to a file. What the script spits out is a set of locative packets that describes the photographs: where they were taken, when they were taken, and who took them. See [Hack #95] for advice on modeling spatial information in RDF. Here's a short sample of an RDF description of photographs taken in Utrecht, September 2004:
5.125718 52.084616 20040906T134632
In English, this description says, "Here is some context about a point in space at latitude 5.1257 and longitude 52.0846. There is a piece of media attached to it. The piece of media was created at this time, and the person who created it has the email address email@example.com."
9.5.2. Create a Dynamic SVG Map with Pop-Up Photographs
Now that we have all that nice photo metadata, what can we do with it other than share it? One quick way to see your photos in relation to a map is to plot them on it using the Scalable Vector Graphics (SVG) format.
The second script, plot_rdf.pl takes the RDF/XML file output by the first script and another file describing a base map with its orientation, and overlays the photos on the map.
This is a slightly more complex task, as first we have to acquire a base map and know how it is georeferenced. That is, we need to know the coordinates of the top left corner, what the extents of the image represent in terms of geographical space, and how the map is skewed or rotated with respect to True North. What a mouthful!
Use the six numbers to create an XML file that looks like the following example, providing a simple description of your map image: its name, its size, and the transformation that the map went through in relation to geographical space. This is the XML file that was used to create a photo map for the GPS/photo info mentioned earlier:
utreg.gif 890 684 10000 0.549457004709508 -0.0298986308382459 0.0250666506000045 -0.52601105571061 -2699.47952280242 2028.02835472852
Finally, you're ready to create a SVG photo-overlaid map. Take the second script, plot_rdf.pl, and run it with the XML image file as the first parameter, and the RDF description of your photographs as the second. It will spit out an SVG file that uses your map as a base layer and has an icon for each photograph, which expands to show a photo thumbnail when you move your mouse over it, as shown in Figure 9-8:
perl plot_rdf.pl utreg.xml utreg.rdf > map.svg
Figure 9-8. A dynamic map with photos appearing as tooltips
9.5.3. See Also
Dav Coleman's write-up of taking geo-annotated photos in real time using a camera phone and a Bluetooth GPS
Flickr, a photo-sharing site
Geolicious, a spatial-media-annotating site.
GPS EXIF metadata
Mappr, a tool for georeferencing Flickr photos by looking up tags in a gazetteer of world place names