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Earth radius (denoted as R 🜨 or R E) is the distance from the center of Earth to a point on or near its surface. Approximating the figure of Earth by an Earth spheroid (an oblate ellipsoid), the radius ranges from a maximum (equatorial radius, denoted a) of nearly 6,378 km (3,963 mi) to a minimum (polar radius, denoted b) of nearly 6,357 km (3,950 mi).
the azimuthal angle φ, which is the angle of rotation of the radial line around the polar axis. [b] (See graphic regarding the "physics convention".) Once the radius is fixed, the three coordinates (r, θ, φ), known as a 3-tuple, provide a coordinate system on a sphere, typically called the spherical polar coordinates.
The fundamental method to create a buffer around a geographic feature stored in a vector data model, with a given radius r is as follows: [4] Single point: Create a circle around the point with radius r. Polyline, which consists of an ordered list of points (vertices) connected by straight lines. This is also used for the boundary of a polygon.
the point's distance from a reference point called the pole, and; the point's direction from the pole relative to the direction of the polar axis, a ray drawn from the pole. The distance from the pole is called the radial coordinate, radial distance or simply radius, and the angle is called the angular coordinate, polar angle, or azimuth. [1]
Extensions to the above notation allow the GEOREF system to be used to designate an area around a reference point. This is achieved by adding an area designation to a base GEOREF co-ordinate. The area designation can be the letter S, to specify the sides of a rectangle (separated by the letter X); or the letter R, to specify the radius of a circle.
Two geofences defined in a GPS application. A geofence is a virtual "perimeter" or "fence" around a given geographic feature. [1] A geofence can be dynamically generated (as in a radius around a point location) or match a predefined set of boundaries (such as school zones or neighborhood boundaries).
The Mercator projection and its use on a world map. This projection first came into use in the 16th century by the Dutch. A circle of latitude or line of latitude on Earth is an abstract east–west small circle connecting all locations around Earth (ignoring elevation) at a given latitude coordinate line.
That point is represented by the entire circular boundary of the map, and the ocean around that point appears along the entire boundary. The Lambert azimuthal equal-area projection with Tissot's indicatrix of deformation. The Lambert azimuthal equal-area projection is a particular mapping from a sphere to a disk.