For a sphere, the gnomonic projection is a projection from the center of
the sphere onto a plane tangent to the center point of the projection.
This projects great circles to straight lines. For an ellipsoid, it is
the limit of a doubly azimuthal projection, a projection where the
azimuths from 2 points are preserved, as the two points merge into the
center point. In this case, geodesics project to approximately straight
lines (these are exactly straight if the geodesic includes the center
point). For details, see Section 8 of :cite:Karney2013.
Classification: Azimuthal
Available forms: Forward and inverse, spherical and ellipsoidal
Defined area: Within a quarter circumference of the center point
Alias: gnom
Domain: 2D
Input type: Geodetic coordinates
Output type: Projected coordinates
Projection String
+proj=gnom +lat_0=90 +lon_0=-50 +R=6.4e6
Required Parameters
None, all parameters are optional for this projection.
Gnomonic (gnom)
For a sphere, the gnomonic projection is a projection from the center of the sphere onto a plane tangent to the center point of the projection. This projects great circles to straight lines. For an ellipsoid, it is the limit of a doubly azimuthal projection, a projection where the azimuths from 2 points are preserved, as the two points merge into the center point. In this case, geodesics project to approximately straight lines (these are exactly straight if the geodesic includes the center point). For details, see Section 8 of :cite:
Karney2013.Classification: Azimuthal
Available forms: Forward and inverse, spherical and ellipsoidal
Defined area: Within a quarter circumference of the center point
Alias: gnom
Domain: 2D
Input type: Geodetic coordinates
Output type: Projected coordinates
Projection String
Required Parameters
Optional Parameters
+lon_0: Longitude of origin (central meridian).+lat_0: Latitude of origin.+x_0: False easting.+y_0: False northing.+ellps: Ellipsoid.+R: Earth radius.Reference: Wolfram Mathworld "Gnomonic Projection" http://mathworld.wolfram.com/GnomonicProjection.html Accessed: 12th November 2009