GPS for 5D3

So here’s the deal with iPhone GPS — I am quite confident in this, for reasons listed at the end:

• The very original iPhone model did not have “real” GPS — it did have some idea where you were, but that only worked based off cell towers and triangulation. It was unquestionably not as good as real GPS.
• All iPhones since, and including, the iPhone 3G (2008) have had true GPS. This means that there’s a GPS antenna in the phone that picks up signals directly from the satellites.
• The GPS in the iPhone is A-GPS. This is actually better than just normal GPS; what it means is that, if it’s available, it will use cell towers and WiFi base stations to help it get a GPS fix faster than normal GPS.
• If an iPhone doesn’t have cell service, it still gets a GPS fix just fine. The “A” part of “A-GPS” doesn’t work, but that’s fine; it means it gets a fix at the same speed as a normal GPS device.
• However, if an iPhone doesn’t have cell service, most apps you have that use GPS will appear not to work — but that’s not because GPS is failing, it’s because they need data to show where you are! For example, the Maps app will show you as a blue dot on a grey background…not terribly useful, but it works. Use the Compass app to get a GPS fix down to seconds of latitude and longitude. There are third-party apps that can download maps ahead of time and show you on them even if they have no data connection; the iPhone’s built in Maps (and Google Maps) don’t do that, however.
• If you turn on Airplane Mode on an iPhone, it disables the GPS receiver, too.

Why do I believe this? Because I've used it. I hiked the John Muir Trail this past August. There’s no cell reception on the entire 220-mile trail except for three small spots, but my iPhone’s GPS worked just fine — the Compass app would locate me down to seconds of latitude/longitude (and third-party programs can give you a fix to much finer precision if needed).

(Also, I work in technology out in Silicon Valley and have several friends who work at Apple — they’ve confirmed this for me.)

Long story short: the iPhone makes a fine GPS receiver, with or without cell service. You need to have the right apps to make much use of it without cell service, which is why it can be confusing, but for geotagging photos, it’s great.

Oh: and HoudahGeo will happily write EXIF to JPEGs, .CR2s, or both.