Geotagging Images for Geoengineers
By Randy Post, PE, GIT
Geotagging refers to adding location information to digital photos. The information can be tremendously useful for a geoengineer in the field. I’m still learning to utilize the technology in my practice, but I thought I would share my experience thus far on the topic. Here are a few possible applications of this technology that might be useful in a geotechnical engineering or engineering geology project:
- Corridor study projects where a large area is covered and photos are used to document existing structures, pavements or geologic hazards.
- Geologic mapping projects where it might be useful to have photos of geologic features either to document them for electronic reports, or to simply refer back to while preparing the final maps or reports.
- Creating virtual field trips for the benefit of clients or others who can’t physically visit a site. I’ve sent Google Earth files to our local geotechnical drilling contractor so he could get a sense of the site without being there.
Obviously there are two main pieces of equipment that you need for geotagging, a digital camera and a GPS. I’m not aware of any commonly used digital cameras with built in GPS, but I’m sure in the future you’ll start to see more of that. Until that time, you can use any digital camera. For GPS, you are looking at either a handheld mapping GPS unit that can records "tracks" as you walk, ride or drive around or a device designed for Geotagging such as the Sony GPSCS1KA GPS Unit or the GiSTEQ GPS Digital PhotoTrackr Lite in Figure 1 below . If you have a Nikon D300 D3 or Fujifilm DSLR camera, you can get an external GPS receiver that will allow the camera to tag the photos as they are taken. Don’t have a GPS and can’t afford one? Don’t worry, you can still manually geotag your photos (discussed below).
Of course, by the time you spend around $150 on a GPS device for geotagging only, you might want to consider buying a handheld mapping GPS unit instead. My company has a Garmin GPSMap 76CS and we have been happy with it over the last couple of years. One nice feature is that it has an external antenna port. This is useful for when you’re in the car, but I’ve also been known to use it in the field to boost satellite reception and allow me to keep the unit in the pouch to continue recording tracks while keeping my hands free (if you tape the receiver to your pack or hat or something). It also has turn-by-turn directions so you can use it in your car, even if it is less cool than some of the dedicated navigation GPS units out right now.
The Garmin eTrex line also allows you to record tracks and download maps (if you pick the right model) but its in a smaller form factor and very well suited to the field. You can pick yourself up a carabiner holster and hang it off your pack or your belt to keep it recording tracks for use in geotagging. No external antenna jack though. I am less familiar with Garmin Colorado 300 and its more expensive siblings, but it has many of the same features of the GPSMap 76CS and is priced similarly but with a nicer screen and a few other nice features as well. I’m not sure, but they may have improved the accuracy with these devices as well. If I had to pick a new GPS for work, I would probably go with the 300. For a slightly less expensive option, I would probably go with the eTrex. I guess you can tell I have an obvious Garmin bias, but I’m sure other brands of GPS can do the job also.
Synchronize your Clocks
Most automatic geotagging programs compare the timestamp on your digital photo with the points in your GPS tracklog. If there is a point on the track (or sometimes a waypoint) at the same time, it uses those coordinates for the photo. Usually there won’t be one at the exact moment you took the picture, so it interpolates. In either case, I think you can see why having the clock on your camera and the clock on your GPS syncronized is so important, especially if you’re taking photos while in the car traveling at a high rate of speed, hopefully as a passenger!
I’m not entirely certain, but I think the GPS might get its time from the satellites. Regardless, it seems to be easier and more appropriate to adjust your camera clock while watching the exact time on the GPS. Set it to the next minute ahead of the GPS time and then accept the new time just as the GPS clock turns over to that minute. If you’re within a few seconds, that should be sufficient. RoboGEO and perhaps other programs allow you to specify a time offset, but I’d use that as a last resort.
In the Field
Check your GPS settings and make sure that it is set to automatically record tracks. Depending on the accuracy you’re after and the amount of available memory on your unit, you might consider changing the frequency of points for your track logs. Then power your unit on and keep it on the whole time you’re taking photos. Like I mentioned, a carabiner or something similar will be useful for keeping your GPS handy but out of your way.
Back in the Office
Once you get back in the office, its time to download your photos and your GPS data. I’d keep a backup copy of you photos in their original format in another folder before you start working. Use the appropriate software for your GPS and save a copy of the tracks and waypoints data in GPX format (GPS Exchange format). This format is what most of the software programs seem to support and you can also import it into Google Earth. I recommend saving the GPS data in your software’s proprietary format as well for later use. I know that with Mapsource, I lose a little information if I try to open the GPX file.