Gnomonic projection
The gnomonic projection (also called the central projection) is a geographic projection characterized by radial symmetry around the central point (centrographic perspective). That is, by means of this projection, any point on a sphere is connected from its center by a line until it intersects in a tangent plane to the sphere (called the projection plane).
Concept
It can be imagined as the projection of a light source on a tangential plane to the Earth, in which the light source is located in the center of the Earth. The scale will rapidly increase from the center to the outside. With this concept great circles are projected as straight lines in the projection plane. The great circle and the center point form a plane that intersects in a straight line in the plane of projection. The smaller circles form conic sections in the plane of projection. This is because the smaller circles form a cone with the center of the sphere through the generatrices, the intersection of the cone forms the corresponding conics.
Uses
The gnomonic projection has several uses in the field of cartography (through the drawing of gnomonic charts) and in gnomonics in the drawing and design of some sundials.
Cartography
In the gnomonic charts made using this projection, every straight line is a terrestrial great circle and the shortest path between two points on the Earth. It is used in aeronautical navigation to plot true courses. A complete hemisphere cannot be represented with this system.
In the polar projection all the meridians are straight lines and are arranged radially, in the equatorial projection the equator and the meridians are straight lines, which are arranged vertically, in the oblique projection the equator and the meridians are straight lines.
Gnomonic
This projection is used in the layout and design of the time scales of some sundials, as well as solar meridians.