| |
What Is GPS?
|
|
 |
GPS is a satellite-based positioning system operated by the United States Department of Defense (DoD). GPS encompasses three segments—space, control, and user. The space segment includes the 24 operational NAVSTAR satellites that orbit the earth every 12 hours at an altitude of approximately 20,200 kilometers. Each satellite contains several high-precision atomic clocks and constantly transmits radio signals using a unique identifying code.
One Master Control Station, five Monitor Stations, and Ground Antennas comprise the control segment. The Monitor Stations passively track each satellite continuously and provide this data to the Master Control Station. The Master Control Station calculates any changes in each satellite's position and timing.
These changes are forwarded to the Ground Antennas and transmitted to each satellite daily. This ensures that each satellite is transmitting accurate information about its orbital path. The user segment, comprised of both civilian and military users worldwide, acquires signals sent from the NAVSTAR satellites with GPS receivers. The GPS receiver uses these signals to determine where the satellites are located. With this data and information stored internally, the receiver can calculate its own position on earth. This positional information can be used in many applications such as mapping, surveying, navigation, and mobile GIS. |
What GPS Can Do for GIS ?
|
GPS is an excellent data collection tool for creating and maintaining a GIS. It provides accurate positions for point, line, and polygon features. By verifying the location of previously recorded sites, GPS can be used for inspecting, maintaining, and updating GIS data. GPS provides an excellent tool for validating features, updating attributes, and collecting new features.
Mobile GIS accesses enterprise GIS in the field. Because GPS provides accurate location information in the field, it is an essential component for mobile GIS. Field inspectors, maintenance teams, utility crews, and emergency workers all require timely access to enterprise GIS data so they can make informed decisions. To facilitate the flow of information to and from the field, mobile GIS solutions leverage advances in wireless technology and the Internet. With mobile GIS, data is directly accessible to field-based personnel whenever and wherever it is needed.
|
How GPS Works |
A GPS receiver must acquire signals from at least four satellites to reliably calculate a three-dimensional position. Ideally, these satellites should be distributed across the sky. The receiver performs mathematical calculations to establish the distance from a satellite, which in turn is used to determine its position. The GPS receiver knows where each satellite is the instant its distance is measured. This position is displayed on the datalogger and saved along with any other descriptive information entered in the field software. |
|
|
|
| |
|
|
|
