GPS Accuracy

Facebooktwittergoogle_pluslinkedin

Today’s Question: In a recent episode of Tim Grey TV you made reference to the GPS receiver in your camera. What happens in a situation where you don’t have a reliable GPS signal? Do you get inaccurate location information?

Tim’s Quick Answer: When there is not a reliable GPS signal, the GPS coordinates embedded in metadata may be inaccurate, or they may be missing altogether. Therefore, it is important to keep in mind that even when location information is embedded in your photos automatically by your camera, the information may not be especially accurate.

More Detail: The implantation of the GPS feature varies among the different cameras that include a GPS receiver. My primary camera (in part because it includes a built-in GPS receiver) is the Canon EOS 7D Mk II (http://timgrey.me/tgtv7d2). This camera (similar to other cameras) will present an indication that the GPS feature is enabled, and that a signal has been acquired.

A variety of factors can impact the accuracy of a GPS signal, so even when you have a “good” signal the resulting coordinates may not be completely accurate. The relative accuracy of a GPS signal is often expressed as a distance. For example, a good signal might represent accuracy within 3 meters, while a not-so-good signal might represent accuracy within dozens of meters or more.

During my current travels I actually experienced several situations where a reliable GPS signal could not be achieved. This happens indoors, of course, but while photographing along the inside passage in Alaska there were a couple of situations where no GPS coordinates were recorded by my camera. For example, when in the Russell Fjord photographing Hubbard Glacier, the surrounding landscape was high enough to interfere with acquiring an adequate GPS signal, and so no coordinates were embedded in the metadata for my photos.

In other situations I have observed GPS coordinates that were not very accurate. In some cases the coordinates may have shown that the photo was captured down the street from the actual location, and in other situations I’ve seen coordinates that were off by more distance, perhaps around half a mile or so. Various factors can impact the relative accuracy of the GPS signal, and different cameras will handle the situation differently. But again, there are circumstances where no GPS coordinates will be embedded in your photos even when that feature is enabled, as well as circumstances where the coordinates that are embedded are less accurate than you would normally expect.

In situations where it is important that you know the location where photographs were captured with some precision, I do recommend reviewing the location information for your photos. You can do this, for example, in the Map module in Lightroom, even moving photos on the map to update GPS coordinates as needed based on the map.