Tuesday, September 04, 2007

Geotagging 101

I take a lot of pictures in a lot of different places, especially since going digital three years ago. I don't always remember exactly where I was when a particular photo was taken.

In the bad old days of film, I would use the date imprint function of both my film SLR and my film point-and-shoot cameras to capture the date a photo was taken. It really ruined any artistic value the picture may have had (which, admittedly, was pretty minimal in those days,) but at least knowing when the photo was taken, I could usually deduce the occasion/location of the subject.

For example, here's an otherwise good picture of the harbor in Vernazza, Italy.
Vernazza, Cinque Terre, Italy
That imprint showing that the photo was taken on April 2, 2003 sure is distracting.

With digital photography there is no need to print dates on photos, because that information, plus a whole lot more, is encoded into the file in the Exif information, which is saved with the digital picture file. Exif stands for Exchangeable image file format, and is part and parcel to all digital photography these days. Your camera is recording it whether you know it or not. Some of the information in the Exif data includes date and time information, camera settings (including aperture, shutter speed, focal length, metering mode, and ISO setting, et al.,) a thumbnail, copyright, and other information.

As an example, here's a picture I took of the moon.
Moon Over Mebane

And here's some of the Exif information on that picture.

I can see that I took this picture on January 2nd around 6 pm. It sure gets dark early in January. So that takes care of the when, but what about the where? In the harbor picture above, I know it's in Vernazza based on the date, plus the fact that I have travel journals that correlate the dates to the places. That's fine if you're in a few, very specific places, but that won't work in all situations.

As an example, I shot a lot of pictures around Manhattan last year at Christmas time. New York City is a photographer's dream, as there is an endless supply of photographic subjects everywhere you look. Too much to keep mental track of, actually. I shot one day, and then struggled that night to remember where exactly where each picture was taken. The next day I went out, and when I'd photograph something, I'd immediately take a shot of the nearest street sign so that I could use that as a geo reference. That may work for alright for NYC, but most places it wouldn't, plus it's not very efficient.

Why do you need to know where a photo was taken, anyway? I guess you don't, but to me it sure makes viewing pictures, especially other people's pictures, far more interesting. When I see something really cool in a photo, I want to know where it was taken. Maybe I'd like to go there myself someday.

The best photo sharing sites allow you to incorporate this information into your photos, and then display them on a map. Conversely, you can surf to a particular location on a world map, and get a quick overview of all the photos taken there. It's a traveler's dream.

For example, here's the map view on Zooomr of L'il Saint Louis in Paris, one of my favorite places in the world. (BTW, the island just to the left is L'il de Cite, where Notre Dame cathedral is located. You've definitely seen pictures of that.)

As you can see, there are three pictures taken on different places on the island (all taken by me, incidentally). You can click on any of the thumbnails to get a full-sized version. What a great way to see what's where.

Now there's two ways to get that location information into the Exif data of your photos: after uploading your pictures to Zooomr, or some other, lesser site, you can point to the right spot on a map, and associate that spot with the picture, or you can tag your pictures before you upload. Google's Picasa (free) software allows you to geotag your pictures with the help of Google Earth, but you still have to remember where each photo was taken. Too much of a hassle. I do it the easy way.

I have a Sony GPS-CS1. It's a GPS (Global Positioning System receiver) that you clip on your camera bag, or strap, or belt, or wherever. . . and it records where you are and when. . . that's it. There's no display. You can't go Geocaching with it or use it to navigate in your car. It has three status LED's, runs for about 12 hours on one AA battery, can hold roughly 160 hours of track logs before you'll have to offload, and is about the size of half a bratwurst. (Ever notice that it always comes back to food with me?). I got mine for about 75 bucks, US.

With the GPS on, you just shoot away with your camera, never worrying about trying to remember where you were when you got "the shot." (Make sure your camera's time setting is correct though. This will be very important later.) When you get back to your computer, you connect the GPS via a USB cable, tell the software what time zone you were in, and offload the time/location data. . . which is just a text file, basically. From there you tell the software what photos were taken in the time frame that the log covers, and it automagically tags the photos with the geo lattitude/longitude data. Even if you lost GPS signal for a while when you were out shooting, the software is smart enough to interpolate your position with pretty decent accuracy. When you upload your photos to Zooomr, the Exif geo data carries through, and Zooomr marks the photo on a world map. Officially, this unit only works with Sony Cybershot cameras. Unofficially, it works great with my Canon too.

So there you have it. Now go out and geotag your pictures. Do it the hard way, or the easy way, but do it. You. . . and the world. . . will be glad you did.


Trevor Carpenter said...

Great post. I've read before about apps that will take your GPS info and "blend" it with your photos and add the data to the EXIF info.

This was some time ago, and now I'm on a Linux machine.

Any chance you know of any good open source apps that will to this? I have a Garmin Etrex Legend C, and I know I can get the basic log off of the unit. I'd love to be able to drag it along on a photowalk.

The Roth Family said...

Trevor: I don't know of an app that will do what you're suggesting, though I don't think it would be all that difficult for someone with some programming skills.

The GPS log is basically a three column table: time (in UTC format), lattitude, and longitude, both in DD.DDDDD format, with one row of data for each 15 seconds the log is being recorded. The software would just have to determine the correct line in the log for each photo, and add that data in the correct format to the exif file.

I really expect more cameras to have built-in GPS as an option some day, as the technology and power consumption are improving dramatically.

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