Absolute Position refers to the location of an object or device determined within a fixed, globally unified coordinate system. It typically refers to a position determined by a global coordinate system (such as latitude and longitude) relative to the Earth’s surface, unaffected by changes in the surrounding environment or reference objects. Absolute position provides not only the object’s latitude and longitude (horizontal coordinates), but also its altitude (vertical coordinate).
Components of Absolute Position
- Longitude: Indicates the position in the east-west direction.
- Latitude: Indicates the position in the north-south direction.
- Altitude: Indicates the vertical position of the object relative to sea level, usually measured in meters (m).
1. Definition of Longitude
- Longitude describes the angular position of a point on Earth relative to the Prime Meridian (0° longitude).
- The Prime Meridian is located at the Royal Observatory in Greenwich, UK, and serves as the starting point for global longitude. The greater the longitude value, the further the location is from the Prime Meridian.
- East Longitude (E): Indicates a position east of the Prime Meridian, with values ranging from 0° to 180°.
- West Longitude (W): Indicates a position west of the Prime Meridian, with values ranging from 0° to 180°.
2. Definition of Latitude
- Latitude describes the angular position of a point on Earth relative to the Equator (0° latitude).
- The Equator is the Earth’s largest circle, dividing the Earth into the Northern and Southern Hemispheres.
- North Latitude (N): Indicates a position north of the Equator, with values ranging from 0° to 90°.
- South Latitude (S): Indicates a position south of the Equator, with values ranging from 0° to 90°.
3. Definition of Altitude
- Ellipsoid Height: The height of an object above the Earth’s reference ellipsoid, typically obtained through GPS or similar devices.
- Geoid Height: The height of an object relative to the Earth’s sea level, taking into account the Earth’s irregular gravitational field (a more accurate Earth model). This is commonly used in fields like aviation and geodesy.
4. Combination of Longitude and Latitude and Data Interpretation
Longitude and latitude, when combined, precisely describe any point on the Earth’s surface. The combination of these two coordinates is frequently used in GPS positioning, map making, and navigation systems.
Common Latitude and Longitude Formats:
- Degrees, Minutes, Seconds (DMS) Format: For example, 40° 42′ 46″ N, 74° 00′ 21″ W. Here, degrees (°), minutes (‘), and seconds (“) represent subdivisions of each degree and are typically used for higher precision positioning.
- Decimal Degrees (DD) Format: For example, 40.7128° N, 74.0060° W. This format is commonly used in modern GPS systems, offering high precision and ease of calculation.
Example:
- 40.7128° N, 74.0060° W, 10m: This is the latitude and longitude of New York City, indicating that it is located at 40.7128° North and 74.0060° West, with an altitude of 10 meters above sea level.
