Geotagging is gaining popularity with photographers to produce geotagged photographs. A few cameras have built-in
geolocation capability. Most, apart from
smartphones, do not, so many photographers rely on external
GPS receivers to determine location. Location may be inserted immediately into the picture file by
tethering with
Bluetooth or suitable wired connection, which are about as rare in cameras as the built-in autogeotagging feature.
GPS units, internal or external, require a lock from at least three satellites (for position), which usually requires up to 60 seconds. However,
acquisition time is decreasing rapidly with hardware improvements. Some 21st-century GPS receivers use cell tower location and one global positioning satellite to obtain a faster lock on location. This assisted GPS (
aGPS) technology is usual in cellular phones. One alternative to GPS is
WiFi triangulation which uses the
MAC addresses of nearby
wireless access points to determine position. Automatic geotagging relies on media acquisition devices that contain GPS, aGPS, or WiFi or other
local positioning systems. Many
camera phones use all these methods: GPS, aGPS, cell tower signals, and WiFi triangulation. Locations may be added later using a user's computer or a
photo sharing web site such as
Wikimedia Commons. It has even been proposed that in future, it may be possible to deduce the locations of photos purely by comparison with large numbers of geotagged photos. These geotagging techniques rely on post-processing of media, recorded
tracks and/or MAC addresses, and cannot be used for real-time geotagging. With the rapid rise of mobile
smartphones which
integrate GPS receivers and cameras, and relative market stagnation of separate devices, these phones are the most numerous instruments for autogeotagging. Those that don't include this ability in their stock software may acquire it by installing appropriate
mobile apps. == Applications ==