In a Nutshell
Geotagging involves recording your position in the world on a time line using coordinates obtained from some of the 24 GPS (Global Positioning System) satellites orbiting the earth. The information is acquired and saved in a log file using a GPS capable device. The acquired data can identify precisely where you were at specific times during the period you were logging your positions.
A signal from 3 different satellites must be accessible to the GPS device you are using to triangulate latitude and longitude. With 4 satellites, altitude can also be determined.
Before recording a position time line, it’s important to synchronize your camera’s clock to the clock in your GPS datalogger. With the clocks synchronized and the time and date being saved to each photo’s EXIF file (Exchangeable Image File Format) by your camera, software can then later be used to match the times and add the appropriate GPS coordinates from your GPS device’s log to each photo’s EXIF file.
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Summarizing in Layman’s Terms
The camera knows what time the photo was taken and that information is already embedded in the photo’s hidden data field. The GPS data logger records where you are (and what time you were there) constantly when it is activated. Software has been written to look at the photo and the GPS log file to match the times and then copy the appropriate location data from the GPS log file to each photo’s hidden data field.
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There are a few cameras available now with built-in GPS capabilities that can be set to include GPS coordinates in the EXIF data automatically. Also, many smart phones such as the iPhone and its competitors provide built-in GPS capabilities, and much of what is discussed on this site will be of interest to smart phone geotaggers. I also plan to test smart phone geotagging features and trail map apps in the future.
But for high quality photographs, most of us in the near future will be relying on GPS dataloggers that stand alone or attach to a camera for generating the time synchronized GPS coordinates necessary for geotagging our images.
There are software tools and photo websites that facilitate adding location data to pictures taken without GPS data logging. I’ll also discuss my experiences with those options, but my priority has been to develop proficiency with “real” geotagging, generating and logging more precise geographic information in real time as I shoot.
Instead of worrying too much today about how we are going to merge the location data with our photographs, let’s focus on first things first. What are we going to use to accumulate and log the GPS data needed to geographically tag our photos?
In the next entry I’ll discuss the Holux M-241 GPS datalogger, my first GPS device.
Important: If you are new to GPS reliant activities, keep in mind that GPS data acquisition is limited by geography and physical obstacles. Architecture, natural features, and being indoors can all inhibit acquiring a position. I’ll be writing more about how to work around those limitations in future entries.
Image: Photo of the backside of the compact Holux M-241 taken on my deck in Colorado. That’s Red Peak at the southern end of the Gore Range in the background. The Holux M-241 GPS datalogger measures 1.26″ x 1.18″ x 2.93″ (32.1 mm x 30.0 mm x 74.5 mm).
