The Global Positioning System (GPS) is a global navigation satellite system developed by the United States Department of Defense, and maintained by the US Air Force. It uses 24 medium Earth orbit (12,500 miles above the earth) satellites, each transmitting precise microwave signals, which enable a person with a GPS receiver to determine their current location, the time, and their velocity.
The satellites circle the earth twice a day, but at any given time, it's rare to pick up even the half on any side of the earth. Fortunately, you only need 3 or 4 satellites to use a GPS receiver to navigate. The signals sent by GPS satellites are not able to reach deeply through solid objects, such as buildings, but the system works well outdoors.
Until 1983, the system was not available to the general public, but after Korean Air Lines Flight 007 was shot down that year, after straying into the USSR's prohibited airspace, President Ronald Reagan issued a directive making GPS freely available for civilian use. Since then, GPS has become a widely used aid to navigation worldwide, and a useful tool for map-making, surveying, commerce, and scientific uses, as well as geotagging.
I remember getting my first GPS receiver, plus software to turn my laptop into road navigation system, years ago. It was so much better than reading maps. It could pinpoint your position as you traveled. It's comforting to know exactly where you are, while driving in a new area. Now, when traveling, I use a portable GPS device to get around (OK, I admit I have some maps as backup, just in case.)
When I first began to experiment using GPS with my photography, there were few GPS receivers built specifically for use with Nikon or other GPS enabled DSLR cameras. The one standout at the time was from Red Hen, however, it cost more than $600. I decided to build my own. Like many, I based my system on the Garmin Geko 301 GPS receiver. I modified the Geko to mount on my camera, as well as the Nikon MC-35 GPS cable, and necessary PC serial cable. The unit worked like a charm with my Nikon D200, but was somewhat unwieldy due to the cabling requirements. Last year, I purchased the Solmeta DP-GPS N2 kit, which is small, and pulls in signals much better than my homemade setup.
Over time, GPS technology has dramatically improved. Receivers are now built with new chip sets which have more ability to receive and decode the L band microwave signals sent by the GPS satellites. When deciding which GPS receiver to purchase for your camera check for:
- Compatibility with your camera.
- Size and cable specifications to determine usability.
- If the unit must be attached to the hot shoe of your camera, or if it can be held on the strap, etc. to free the hot shoe for use with your flash.
- If the unit is plugged into a camera port which is used for other purposes, if a splitter is available for simultaneous use of the port with another device.
- If it has it's own power supply (preferable) or uses power supplied by the camera.
- If it has a built-in PNI Electronic Compass, as some cameras can record the direction the camera was pointed when the photograph was taken.
- If it has an auto indoor GPS position fixed mode, so that it will allow the camera to use the last GPS position received, to store with photos taken, while the camera is used inside.
- The sensitivity of the GPS unit to receive data, even in adverse conditions such as bad weather, among tall buildings in cities, and amid forested areas.
- The software must be able to read your camera's Exif data directly, edit it, add new data to it, and use it for mapping purposes.
- In order to create export files, the software must be able to pull the data directly from photos from a list of your choosing.
- Is the software capable of stamping the photos themselves on their face, if desired, with time and GPS information?
- Can the software use Google Earth to directly geotag photos missing GPS information?
- Can the software geotag photos from place names, or IPTC locations?
- The software must be able to create Google Earth KML and KMZ files to create maps of your photos on Google Earth.
- The software must be capable of exporting geotagged photos to Google Maps, Flickr and Yahoo Maps, MapPoint, Shapefiles and create DXF files to be used in 3rd party utility programs.
- The software should be capable of use in GPS Visualizer, an excellent personal mapping web site.
The map sure answers the question, "Hey, exactly where is that?" doesn't it.