There are countless photo sites on the Web, but be prepared to spend a lot of time with this one:

GigaPan (www.gigapan.org) is an online collection of ultra-high resolution landscape photos taken by people all over the world, using a combination of ordinary digital cameras and robotic technology.

The site and the technology behind it were designed to link people around the planet.

Most digital photographers think in terms of megapixels when evaluating the quality of an image. But the GigaPan robotic camera mount enables even the humblest of digital cameras to take photos that are measured in gigapixels -- or 1 billion pixels -- instead.

The GigaPan was developed at Carnegie Mellon University, in collaboration with NASA's Ames Intelligent Robotics Group. It's also one of the CMU-developed technologies employed in the citywide Robot 250 exhibits on display this month (robot250.org), including the GigaPan Student Project at The Andy Warhol Museum, an exhibition of six murals by local students now at the Alcoa Business Center, directly behind the museum.

On the GigaPan Web site, you'll find photographs that are extreme wide-angle views of well-known and lesser-known places -- from the Grand Canyon and city skylines to familiar neighborhood street scenes. They're stunning panoramas, but the fun with these photos is just beginning. These are images that not only can be looked at, but explored.

Clicking on individual images yields a larger photo, which can be zoomed in on and navigated to reveal richer detail, giving the viewer an almost virtual reality tour of the place. For example, a city skyline can be magnified to focus in on a single building or person on the street, and a panorama of a national park can zero in on a herd of elk -- or just one of them -- grazing there.

Images are organized by most popular, most recent and by tags, for example, photos of oceans, mountains and Pittsburgh or other cities. Images can also be submitted for inclusion in Google Earth's GigaPan layer.

Photographers don't need to have the robotic mount to create images for the site. They can take a series of overlapping digital images and use software that stitches them together to create the panoramic view. Free photo uploader software will be available through the GigaPan site in August, and release of a free stitching application is also in the works.