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You're in Prague for 6 days with your camera (shooting in raw format), packing your data logger for geotagging, and your MacBook. At the end of each day you plan to download your images and track logs to geotag them before processing via Adobe Bridge. Given this scenario how do GPSPhotoLinker and PhotoGPSEditor—two free Mac apps—stack up against two commercial alternatives, Geophoto and HoudahGeo?

What features are important?

Below are the main characteristics I would look for in geotagging software, bearing in mind the above scenario. My interest here is purely the "business end" of geotagging i.e. writing the data from my logger to my images. As such my ratings reflect fitness for this purpose and do not necessarily cover the full feature set of the individual applications.

Load multiple GPX track logs simultaneously: If your logger is as energetically challenged as the Holux M-241 you won't be leaving it in your bag and forgetting about it until the end of your 9 hour sojourn through the Old Town. You'll want to switch off logging during meal breaks, or inside galleries when you won't be using your camera (for example). Thus each daily download of photos could be associated with several distinct track logs, each potentially covering different activities. While you may be able to download a combined log (as you can with the Holux and BT747) you might wish to retain the individual logs, a useful option if you intend to archive the log/ KML export directly with the relevant images (e.g. from the day trip to Kutná Hora).

Load photos in NEF format: Personal preference—I'd rather store the geodata in my raw archive for all images, as opposed to adding the data to selected images after processing to JPEG. Not all geotagging software can handle images in raw formats.

Adjust track/ camera offset: Setting you camera and logger to the same time (e.g. GMT) negates the need for this option to some extent, but all time-keeping devices gradually become out of sync. Having this option also allows you to geotag photos taken with other cameras (your iPhone, point-and-shoot, etc.) that might not have been synchronized in advance.

Acquire IPTC metadata while offline: IPTC headers (e.g. city, country) are useful to metadata-aware applications such as CDFinder (see my review) or Spotlight that can make use of them as search terms. Although typically added automatically, this tagging process usually requires interaction with an Internet-based server. The budget-conscious traveller may not which to utilize an expensive hotel broadband service.

Check time to nearest point for each photo: If your logger is recording track points every five seconds, you know that the nearest point should always be within this time interval. If the nearest recorded point is 26 min 17 sec away, something's gone wrong. Were you getting a GPS fix? When did the logger's battery die? Did you neglect to adjust the time zone?

Check position on map before geotagging: If your geotagging software suggests a matching track point for a given photo, it's reassuring when you can select an image, click on a "view on map" link, and zoom in using satellite view to confirm that the position actually matches your recollection of where you took that image. Do this randomly a few times and you can be confident that automatic geotagging is up to par.

Ginger and Fred, taken adjacent to the "botel" Matylda as indicated

Manual matching to waypoint: The Holux M-241 like many loggers has the ability to record waypoints. Instead of automatically recording thousands of track points—few of which are associated with a photo—you manually push a button to "mark" a location, and later load a list of time-stamped waypoints to which you match the EXIF time-stamp in each photo. This makes sense, for example, if you want to produce a KML file for viewing in Google Earth that shows markers only at photo stops—and not an overlapping stream of meaningless track point markers that obscure your view of the route!

Batch save coordinates to original photos: Having satisfied yourself that matching is accurate, you'll want to write the geodata to EXIF-GPS and IPTC headers for all photos with minimal effort. Furthermore, because writing this data does not degrade the image or other EXIF attributes, there's no reason not to store it in the original NEF files for archiving.

Specify tolerances for automatic matching: It's a matter of trust. When batch-saving geodata to your images you might be happy with "nearest" track point. But what if the nearest point is 50m or 2min 3sec away in that image you didn't verify using "view on map"? Specifying matching tolerances allows you to quickly identify any images that fall outside of the expected pattern.

Intuitive interface: If you can sit down in front of new software and start using it, without having read the manual, that's a good start. There should be few clicks involved in a streamlined workflow, although supplementary features shouldn't be too hard to find or use. The application should have form as well as function, but the one shouldn't be at the expense of the other.

GPSPhotoLinker

Website: Jeffrey Early
Cost: Free
Version tested: 1.6.0b6

GPSPhotoLinker uniquely allows specification of tolerances for batch geotagging

Load multiple GPX track logs simultaneously: Yes

Load photos in NEF format: Yes

Adjust track/ camera offset: Yes (time zone, hours, minutes, seconds)

Acquire IPTC metadata while offline: No (requires terraserver-usa.com)

Check time to nearest point for each photo: Yes (preceding, time-weighted average, next)

Check position on map before geotagging: Yes (various mapping services)

Manual matching to waypoint: Yes

Batch save coordinates to original photos: Yes (using nearest recorded or time-weighted average point)

Specify tolerances for automatic matching: Yes (by max distance between points and/or time to nearest point)

Intuitive interface: Yes

Score: 9/10

Tip: For accurate matching remember to uncheck Use system time zone and set Photos' Time Zone to GMT (if that's what you've set in your logger & camera); this setting is easily overlooked as it is distinct from Shift Time.

PhotoGPSEditor

Website: MMISoftware
Cost: "Free"
Version tested: 1.5.4

PhotoGPSEditor's wizard offers several methods of determining offset

Load multiple GPX track logs simultaneously: Yes

Load photos in NEF format: Yes

Adjust track/ camera offset: Yes (by map, by coordinates, by time)

Acquire IPTC metadata while offline: No (requires terraserver-usa.com)

Check time to nearest point for each photo: Yes (in Advanced mode can choose specific track point to match to given photo)

Check position on map before geotagging: No

Manual matching to waypoint: No

Batch save coordinates to original photos: No (NEF duplication so slow app seems unresponsive)

Specify tolerances for automatic matching: No

Intuitive interface: Yes (Wizard or Advanced), but embeds advertising and donation/ TrialPay naggs.

Score: 4.5/10

Geophoto

Website: Ovolab
Cost: $US24.95
Version tested: 2.1.1

Disclosure: A single user license for Geophoto was provided by Ovolab for the purposes of this evaluation.

Geophoto adds IPTC headers even offline; shame the coordinates are wrong

Load multiple GPX track logs simultaneously: No (for single logs import via Item menu not available until photos loaded into scrapbook)

Load photos in NEF format: Yes (but not directly from folder or card—must create scrapbook then import duplicates before selecting images to process in strip)

Adjust track/ camera offset: Yes (by date, time, time zone—but dialog does not fit MacBook display so unusable, I needed to add a ficticious 1h offset to show correct position, and image at 14:42 reported as outside track range of 14:01–16:38h; NB must re-select your images and tick checkbox at bottom to activate Apply button)

Acquire IPTC metadata while offline: Yes (but does not save it to photo despite displaying it, unless you right-click on the images in the strip, choose Set Location, then tick the checkbox for Also set city and country tags, then re-save—although doing so deletes altitude!)

Check time to nearest point for each photo: No

Check position on map before geotagging: Yes (using Google Maps)

Manual matching to waypoint: No

Batch save coordinates to original photos: Yes (must manually select all in strip and choose Update Original with Location Information; to add IPTC headers see above)

Specify tolerances for automatic matching: No (but can set threshold for track point interpolation)

Intuitive interface: No (eye candy defeats usability; no fluid workflow for automatic geotagging)

Score: 3/10

HoudahGeo

Website: Houdah Software
Cost: €25
Version tested: 1.4.2

HoudahGeo's 3-step workflow exemplifies ease-of-use

Load multiple GPX track logs simultaneously: Yes

Load photos in NEF format: Yes

Adjust track/ camera offset: Yes (time zone, seconds)

Acquire IPTC metadata while offline: No (requires geonames.org)

Check time to nearest point for each photo: No

Check position on map before geotagging: Yes (Geo menu, using Google Maps or Google Earth)

Manual matching to waypoint: Yes

Batch save coordinates to original photos: Yes

Specify tolerances for automatic matching: No

Intuitive interface: Yes

Score: 7/10

What about reverse geocoding?

What if you don't have Internet access at the time you geotag, as was the situation in my hotel room? What if you're using a GPS device attached to your dSLR camera that adds coordinates on the fly, as Jason asks? Can you go back and "reverse geocode" to add IPTC metadata to your images?

Jason was able to add street name, city, and country IPTC headers via existing coordinates in EXIF-GPS using Microsoft Pro Photo Tools (Windows only), but you can reverse geocode on the Mac too.

In Geophoto create a scrapbook, import your images, select them in the strip, choose Set Location from the Item menu, click Set, re-select the image in the strip and right-click to choose Update Original with Location Information. This will add attributes for city, country code, country name, and province/ state—whilst destroying recorded altitude.

In HoudahGeo after loading your images simply select Reverse geocode all from the Geo menu to add city and country attributes, and click the Write EXIF button.

In GPSPhotoLinker loading and selecting the photos, going to Batch mode, unchecking Ignore previously geotagged photos, and clicking Batch save to photos might be expected to work, but it doesn't and instead strips all existing data. It's a similar story for PhotoGPSEditor.

Conclusion

GPSPhotoLinker gets my vote: it does what it does with minimum fuss and inspires a high degree of confidence in its automated processes. Those with time sync trouble may be drawn to the offset flexibility of PhotoGPSEditor, although may be put off by the checkout requests that don't sit so well with "free". Pretty much everything was a chore in Geophoto; it couldn't make things more complicated if it tried. HoudahGeo is the antithesis, delivering a clean and highly intuitive interface making it easiest to use, and the best choice for reverse geocoding.

If your main interest is in sharing features (not evaluated here), you'll probably focus on the commercial choices.

Incidentally, to upload to Flickr direct from iPhoto I use FFXporter (free) which preserves geodata. If I wanted to export a particular image to KML for viewing in Google Earth, I'd use iPhotoToGoogleEarth (free).