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Apple has just released iLife ‘09, introducing geotagging as an iPhoto feature called ‘Places’. As usual, Apple is not so much a pioneer of new technologies but rather adapts to popular trends that have reached a serious momentum. So it is worth having a closer look at geotagging and the available software for the Mac.

Apple's iPhoto displays locations of images as pins on a map.

In this first post of the “Geotagging and the Mac” review series we will look at the basics of geotagging, see what features and workflows are essential. The conclusions are independent of the operating system you are using.

In subsequent posts, we will have a closer look at available MacOS geotagging applications and see whether they meet our criteria. The main objective of our search is to identify a smooth and reliable workflow to help you get your groundwork done efficiently.

“Define your terms” is alway a good starting point for any review. So, a few preliminary thoughts on geotagging basics are in place.

Travelling Standards

Geotagging

Geotagging is the process of merging geographic coordinates with individual images or other documents. This may pinpoint the location where an image was taken or where a specific information is referring to. Also, from a timeline perspective, a group of images can be attributed to waypoints along a specific track.

The most universal values for coordinates are longitude and latitude, which are the most basic geotag components. They are commonly retrieved from a GPS unit or a mapping application (or from my enhanced live map here).

There are quite a few purposes for geotagging: to illustrate your recent holiday blog, to find pictures of a specific location you are planning to visit, or for varied documentation needs (say, if you happen to be a building surveyor, a crime scene investigator, or just plain pedantic).

Please note that geotagging is about adding coordinates to your files while geocoding is about retrieving coordinates from other geographic information, e.g. by entering an address in Google Maps.

The EXIF Standard

The EXIF specification contains a list of GPS-related fields.

As there are so many different uses and applications for geotagged images, standards are very much needed, and this is the good news: longitude, latitude and elevation values can be stored into most pictures as part of their EXIF metadata header, a descriptive section within the image file. There is very little trouble with compatibility, so that geotags can be read by most programs you are likely to use, including iPhoto, Photoshop, and even Preview.

However, writing geodata is a very specific task, as the EXIF header is generally read-only. This is where geotagging applications come into play.

The IPTC Standard

Adobe Photoshop provides a dialog for reading and writing IPTC location data (in the file information menu).

Additional geo information can be written into the IPTC metadata header: usually the names of the location or street, city, state and country. Most image processing applications can read and write IPTC, so it is easier to modify than EXIF.

However, the IPTC metadata standard requires a little more caution when working with RAW files from digital cameras, because those often depend on external XMP “sidecar” files to store this information. IPTC also has language issues (how would you spell the Russian capital’s name? Moscow, Moskva or Москва?). Yet once the EXIF coordinates are set correctly, location names can be retrieved at any time.

The difference between EXIF and IPTC is easy to remember: EXIF holds technical information about the picture – aperture, shutter speed, creation time etc. – while IPTC is a descriptive section for the picture’s content, such as author, title, caption etc.

MacOS Preview displays geodata as a world map with crosshairs and a button to launch Google maps. For this part of the EXIF header, Preview displays a separate GPS tab.

Meta Luggage

In times of fast moving technical development and relatively short software lifecycles, the second metadata imperative after standardisation is “let the data travel with the file”. This seems obvious but many programs keep metadata information in their proprietary databases rather than storing it into the image files directly.

Travelling files, however, are now a very common phenomenon, as the same images are often used online just as much as offline and in many different applications simultaneously. Another reason for relocation may be that you – like myself – happen to buy a Mac after a decade of Windows and face migration issues (very few, but still).

Finally this is all about archiving: if you want to enjoy showing those pictures to your grandchildren some day, the images and the scribble on their backs should last longer than the applications they were first archived with.

Caveat

There is one big caveat when it comes to modifying metadata: just like with your travelling luggage, parts of the metadata may get lost due to improper handling. Unfortunately, a big number of applications will erase existing metadata when writing or modifying other entries. This may be due to outdated application versions that reflect the metadata mess of by-gone days or  it is – quite frankly – the result of embarrassingly incompetent programmers.

It is a sad fact that even leading applications have issues in that direction. An analysis of metadata handling of Apple’s Aperture, Adobe Lightroom and GIMP that I did about a year ago, showed significant incoherence. Even worse, some Adobe applications would mismatch entries created by their siblings from the same generation.

But this caveat goes even further: some applications cripple metadata even if you do not attempt to modify it. Simply opening and saving an image file will wreak havoc. You may realise what happened only much later, as you probably do not monitor your metadata panel permanently.

So, have a closer look at the applications you are using to avoid trouble. The International Press Telecommunication Council recently issued a list of applications that claim to be standards compliant. If you want to check exactly what your favourite program does to your metadata, have a look at the “Reading All Metadata” section of my “ExifTool and the Automator” post.

Travelling Standards Summary

• The most important location data (longitude, latitude) is stored into the EXIF metadata section of an image file by specialised geotagging software.
• The IPTC metadata section provides room for a more detailed verbal description of the location.
• For archiving reasons, it is a very good idea to keep all geodata information stored within the image file it refers to.
• Applications should be tested for non-destructive metadata handling.

Workflows

There are two main approaches to a geotagging workflow: either you have a track log from a GPS unit that you want to merge with your images or you want to insert geodata manually into existing pictures. Even if you possess a camera with integrated GPS logging (or retrieve images from an iPhone), you will want to have a second look at the data as tracking quality varies depending on satellite reception.

• Log-based workflow: we have a track log from our GPS device and want to merge it with our images.
• Manual workflow: we don’t and want to click-tag. Or we do, but some images need re-positioning.

Both workflows are pretty time-consuming if you want to obtain reliable results. And if your focus is on photography or whatever business is behind your geotagging interest, you want to get it over with quickly while not sacrificing quality. Therefore it is important to establish the core requirements for such a workflow.

The “reliable” accuracy level of course depends on your getoagging purpose. My personal rule of thumb is that if coordinates are within 5-10 meters from the original location I can live with the result of a batch job. For me, it suffices that the spot can be found easily by just looking around.

GPS units - like this Garmin handset - continuously store location data into track log files that can be used for geotagging. For photography purposes there are smaller geo loggers available, usually without a display and small enough for any camera bag.

Nine Universal Requirements

Here are nine universal requirements for the geotagging workflow:

1. Support for most common image formats (JPEG, TIFF, PNG, and various RAW formats including Adobe’s DNG)
2. Support for image libraries such as those of iPhoto, Apple’s Aperture or Adobe Lightroom
3. Support for most common track logs (GPX, NMEA etc.) or direct link-ups to GPS units
4. Batch adjustment of time zone and time offset
5. Waypoint administration to let you adjust your tracks, file or categorise them
6. Batch insertion of geotags from track logs, writing latitude, longitude and altitude values; ideally with preferences for the interpolation method
7. Map-based geotagging with point-and-tag feature (cross-hairs!); alternative map views (satellite, map, terrain) are essential for manual tagging; ideally including location search and alternative mapping providers
8. Output saved in EXIF and IPTC or XMP headers of original file; IPTC data for camera RAW files stored in XMP sidecar files
9. Output to a KML/KMZ file to view images in the context of a map

Nos. 1-3 are low priority, as these are rather individual requirements and most formats can easily be converted if needs be.

No. 4 is crucial: sometimes the camera’s time does not match the GPS device’s. A few seconds difference may result in a misplacement of a kilometre or more, depending on the number of waypoints your device creates, your travelling speed and the interpolation method used. (BTW: I prefer to have my camera set to UTC as time reference, no matter where I travel. This helps to avoid confusion with local time zone and daylight saving time issues.)

No. 5 helps to adjust the sometimes highly erratic tracks created by GPS devices, but is also a little off our own track: there are specialised tools that will do that job better. (Of the prominent geotagging applications, myTracks does the job quite well, though.)

Nos. 6-8 are what we are talking about here: geotagging central. For both positions 6 and 7, a reverse geocoding option – i.e. automatic insertion of IPTC location values such as city or country – is a nice-to-have.

When working with maps, offline tagging may be essential for you. But as no consumer mapping application stores all maps, terrain and satellite data locally, a limited functionality is to be expected. A possible workaround is with a Google Earth integration and your target area already in cache.

No. 9 is very useful for turning the result into standardised visual tracks, so I would call it a really-really-nice-to-have feature, but it is not high priority in this context. We will not consider other exporting options here – such as Flickr or Facebook uploads – as this is too much everybody’s own taste. Below are a few examples what a KML/KMZ file with images can be used for.

KML files with images can be viewed using Google Earth.

Google Maps can reference to external KML files and display waypoints together with the associated images.

Post Summary

• A foresighted geotagging approach requires standards and coherent data storage, represented by EXIF location data stored within the image file.
• Reliable geotagging workflows – whether manual or batch process based – should require little intervention, except for adjusting individual coordinates or time shifting a set of subsequent waypoints.

Related Posts

• All posts in “Geotagging” category
• Geotagging and the Mac (2) – Test Scenario
• Geotagging and the Mac (3) – iPhoto ‘09 “Places”
• Geotagging and the Mac (4) – HoudahGeo
• Geotagging and the Mac (5) – Google Picasa

Dictionary Links

• DST – Daylight Saving Time
• DNG – Digital Negative: non-proprietary RAW format
• EXIF – Exchangeable Image File Format: metadata specification
• Geocoding: retrieving coordinates from other geographic information
• Geotagging: adding coordinates to images and other media types
• GPS – Global Positioning System
• GPX – GPS eXchange format: XML schema for geographic annotation
• IPTC – International Press Telecommunications Council’s information interchange model: metadata specification 
• JPEG or JPG – Joint Photographic Experts Group’s image specification: image file type
• KML/KMZ – Keyhole Markup Language/zipped version: XML schema for geographic annotation and visualisation
• NMEA – National Marine Electronics Association: data specification for communication between marine electronic devices, e.g. GPS receivers
• PNG – Portable Network Graphics: image file format
• RAW – generic term for “raw” i.e. unprocessed image file formats (NEF, CRW, CR2 etc.), usually created by high quality digital cameras
• TIFF or TIF – Tagged Image File Format
• UTC – Coordinated Universal Time: time standard, can be used as synonym for Greenwich Mean Time (GMT) for photographic purposes
• XMP – eXtensible Metadata Platform: unifying metadata specification

Updates

• March 7th, 2009: added “Caveat” section
• March 8th, 2009: added reference to IPTC in “Caveat” section
• March 23rd, 2009: added reference to my live map
• March 27th, 2009: added reference to “Reading All Metadata” section
• April 3rd, 2009: replaced “Upcoming Posts” with “Related Posts” section
• April 18th, 2009: added alternative maps/mapping providers and offline tagging to 9 requirements

Tags: Geotagging, Metadata, Review, Software

This entry was posted on Wednesday, February 25th, 2009 at 4:18 pm and is filed under Geotagging, Reviews. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.