Cameras with satellite-navigation features and switches that ensure subjects are smiling are among the highlights of the Photokina trade fair that opened on Tuesday.

The fair, held every two years in Cologne, is a major venue to launch new digital and film cameras, camera-phones, camcorders, lenses, flash systems, photo printers and software.

More than 1,520 exhibitors from 49 nations are attending the six-day event, described by its organizers as the world's biggest camera show.

Some of the cameras on display have global positioning system (GPS) applications which record the exact location on the earth of the picture.

On a camera-phone, such a picture can be sent to another sat-nav- enabled phone. The second phone can then be used as a navigation device to guide the way to the scene, or onwards to a nearby restaurant, thanks to map data in the device.

Also on display is Sony's new camcorder with a feature known as the smile shutter which can recognize facial expressions, a spokesman said.

The device, shown earlier this month at the IFA consumer- electronics show in Berlin, grabs still photographs out of the video stream where the subjects are smiling and saves them as portraits.

Photokina is also showing compact cameras with interchangeable lenses, a feature previously reserved for the more upmarket single-lens reflex cameras.

Digital cameras dominate the exhibition, but although sales are booming dealers said there was not a great deal to earn on them because the prices were so low.

Camera phones at the show are to feature bigger displays and software to reduce the effects of camera shake, just like regular digital cameras.

Among the specialized equipment at Photokina will be heat-seeking cameras that can "see" warm surfaces in dark and fog, or detect heat leaks in insulated buildings.