Yes - in fact they are designed for each other. The 5D III has the ability to communicate with the GP-E2 via the hot-shoe terminal (as compared to, say, a 7D where an external cable is required -- no external cable is required for a 5D III.)
Additionally, when you are reviewing images on the 5D III and using the "info" button to see more data, the 5D III will display the GPS data if that image was taken while using the GPS. Basically the 5D III's menu system already includes the firmware programming to configure and control the unit.
The only requirement for the 5D III is that the firmware version has to support it. The original version of firmware for the 5D III did not... but all subsequent revisions do support it. So if you are keeping your firmware up to date then you are good to go.
Also... one little nicity of the GP-E2 over other GPS units is that it also has an electronic compass built-in. So not only does the camera know where you are, it also knows which way the camera is pointed (and adds that meta-data to the image.)
It runs on a single AA battery.
It has the option of creating a "log" (I don't use that feature). This creates a file that you can import (via USB connection). The file is a KMZ file (Keyhole Markup Language -- Zipped) and is compatible with, for example, Google Earth (KMZ is not a Canon proprietary format.)
And for power saving purposes, you can choose how often it updates your location. Intervals can be set to as frequent as every 1 second, or as infrequent as once every 5 minutes (lots of intervals in between). At the 1 second interval the battery lasts about 10 hours. At the 5 minute interval the battery would last nearly 4 days (but that's continuous use).
I use mine for a few hours at a time (I don't use it all day long) and still find that I can go for days before I need to swap the battery (I use Sanyo Eneloop rechargables and always have a spare in the bag.)
I use Aperture on the Mac to manage all my images. Aperture fully supports the geo-tagging feature - so when I import images, the software can show me a map of where they were taken. I believe LIghtroom also supports this (but I'm not a Lightroom user) -- the point is, no extra plug-ins or utilities had to be installed on my computer since the photo adjustment and management software I use already knows how to deal with the embedded data.
Tim Campbell
5D III, 5D IV, 60Da
