An Introduction to Prune

Plotting Data

If you have the gnuplot tool installed on your system, you can use Prune to turn the dry GPS data into colorful charts. To do this, choose View | Chart and use the Charts dialog window to specify chart settings. Select, for example, the Time option for the X-axis and Speed for the Y-axis to generate a chart that displays your speed profile (Figure 4). Either output the generated chart directly to the screen or save it as an SVG file that you can tweak in a vector drawing application such as Inkscape.

Prune can export the currently opened GPX file in several formats. The File | Export GPX command lets you save a tweaked GPX file under a different name, whereas the Export KML command can be used to save the GPX file in the Google Earth-compatible format, which allows you to display GPS data in the Google Earth application. To do this, export the currently opened GPX file, choose File | Open in Google Earth and select the exported KML file (Figure 5).

Using Prune as a Photographic Tool

Thanks to its ability to correlate photos, Prune can also be an indispensable tool for shutterbugs. But what is photo correlation and how does this feature work in Prune? If you have a digital camera, you can take photos while recording your geographical coordinates with a GPS device. Then you can open the GPX file in Prune, map your photos onto the track, and write the coordinates to the photos (i.e., geotag them). This way, you can geotag photos even if your camera doesn't have geotagging capabilities.

Correlating photos with Prune is a straightforward process. Just choose Photo | Add photos and select the photos you want to correlate. Prune can automatically correlate photos by matching the timestamp of a photo with the timestamp of a track point. To perform the automatic correlation, choose Photo | Correlate photos.

For successful correlation, the clocks in your camera and GPS device must be synchronized; otherwise, Prune will prompt you to specify a time offset. Although you can even map old photos onto a newly recorded GPX track, you will need to correlate all such photos manually.

To do this, go to the Photos list in the left panel, select a photo, press and hold the Ctrl key, and select the point you want on the map (Figure 6). Then, choose the Photos | Connect to point command. To write geotags to the photo, use the Photos | Save to Exif command (this requires that the ExifTool utility be installed on your system).

This feature is nifty, indeed, but Prune has yet another trick up its sleeve. When you export the GPX track containing correlated photos in the KMZ format, Prune generates thumbnails and bundles them with the .kmz file. In this way, you can view the correlated photos in Google Earth.

Final Word

Prune is the perfect companion to any GPS device because it's simple to use and offers all the essential features needed to view and edit GPX files. Additionally, its correlation capabilities make it a great tool for photographers. Add to this the ability to export GPX tracks as KML files, and you have a very useful application for all your GPS needs.

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