A great-circle segment on the Earth ellipsoid is the shortest route between two points on the ellipsoid surface. It is also called an orthodrome, or a geodetic or geodesic route, or just a geodesic.

The "great-circle" term, which is borrowed from spherical geometry, cannot be taken literally on the ellipsoid, since the shortest route on an ellipsoid is usually not a circle, nor even an ellipse (you cannot construct it by cutting the ellipsoid with a plane).

When a great-circle segment is used by a 3D method in the Crs class, it is assumed that altitude varies linearly with horizontal distance between two nodes.

An approximate great circle. Some Crs methods can accept this line type, for faster but less accurate results.

A rhumb line, also called a loxodrome, is a curve with a constant bearing or azimuth: that is, it intersects each meridian with the same angle. It is not the shortest route on the ellipsoid, except if it is a meridian or the equator.

With older navigation systems, it was easier to split up a route into smaller rhumb-line segments. Modern systems can handle the continuously changing bearing of the great-circle route, but there is still a strong tradition of using rhumb lines in navigation to define waypoints etc.

A rhumb line looks straight on a MercatorProjection map. When an oblique rhumb line approaches a pole, it becomes a spiral that goes around the pole an infinite number of revolutions, but its length to the pole is still finite. An oblique rhumb line has no well-defined direction at the pole.

M. C. Escher's woodcut Sphere Surface with Fish shows black and white fish swimming along eight rhumb lines of a sphere.

When a rhumb line is used by a 3D method in the Crs class, it is assumed that altitude varies linearly with horizontal distance between two nodes.

A truly straight line in 3D space. This line type is supported by Crs methods whose names end with "3D", and also by the methods Crs.Route, Crs.AzimuthFromLineSegment and Crs.PitchFromLineSegment. It is not supported by other Crs methods designed only for 2D calculations, but the footprint of a straight 3D line is very nearly a great-circle route, so the GreatCircle line type can be used instead. (The footprint would be a great-circle route if the earth were modelled as a sphere.)

Note that light rays and radio signals in the earth atmosphere do not follow a straight 3D line precisely, mainly due to atmospheric refraction that tends to bend the rays downwards.

A great-circle segment on the Earth ellipsoid is the shortest route between two points on the ellipsoid surface. It is also called an orthodrome, or a geodetic or geodesic route, or just a geodesic.

The "great-circle" term, which is borrowed from spherical geometry, cannot be taken literally on the ellipsoid, since the shortest route on an ellipsoid is usually not a circle, nor even an ellipse (you cannot construct it by cutting the ellipsoid with a plane).

When a great-circle segment is used by a 3D method in the Crs class, it is assumed that altitude varies linearly with horizontal distance between two nodes.

An approximate great circle. Some Crs methods can accept this line type, for faster but less accurate results.

A rhumb line, also called a loxodrome, is a curve with a constant bearing or azimuth: that is, it intersects each meridian with the same angle. It is not the shortest route on the ellipsoid, except if it is a meridian or the equator.

With older navigation systems, it was easier to split up a route into smaller rhumb-line segments. Modern systems can handle the continuously changing bearing of the great-circle route, but there is still a strong tradition of using rhumb lines in navigation to define waypoints etc.

A rhumb line looks straight on a MercatorProjection map. When an oblique rhumb line approaches a pole, it becomes a spiral that goes around the pole an infinite number of revolutions, but its length to the pole is still finite. An oblique rhumb line has no well-defined direction at the pole.

M. C. Escher's woodcut Sphere Surface with Fish shows black and white fish swimming along eight rhumb lines of a sphere.

When a rhumb line is used by a 3D method in the Crs class, it is assumed that altitude varies linearly with horizontal distance between two nodes.

A truly straight line in 3D space. This line type is supported by Crs methods whose names end with "3D", and also by the methods Crs::route, Crs::azimuthFromLineSegment and Crs::pitchFromLineSegment. It is not supported by other Crs methods designed only for 2D calculations, but the footprint of a straight 3D line is very nearly a great-circle route, so the GreatCircle line type can be used instead. (The footprint would be a great-circle route if the earth were modelled as a sphere.)

Note that light rays and radio signals in the earth atmosphere do not follow a straight 3D line precisely, mainly due to atmospheric refraction that tends to bend the rays downwards.

A great-circle segment on the Earth ellipsoid is the shortest route between two points on the ellipsoid surface. It is also called an orthodrome, or a geodetic or geodesic route, or just a geodesic.

The "great-circle" term, which is borrowed from spherical geometry, cannot be taken literally on the ellipsoid, since the shortest route on an ellipsoid is usually not a circle, nor even an ellipse (you cannot construct it by cutting the ellipsoid with a plane).

When a great-circle segment is used by a 3D method in the Crs class, it is assumed that altitude varies linearly with horizontal distance between two nodes.

An approximate great circle. Some Crs methods can accept this line type, for faster but less accurate results.

A rhumb line, also called a loxodrome, is a curve with a constant bearing or azimuth: that is, it intersects each meridian with the same angle. It is not the shortest route on the ellipsoid, except if it is a meridian or the equator.

With older navigation systems, it was easier to split up a route into smaller rhumb-line segments. Modern systems can handle the continuously changing bearing of the great-circle route, but there is still a strong tradition of using rhumb lines in navigation to define waypoints etc.

A rhumb line looks straight on a MercatorProjection map. When an oblique rhumb line approaches a pole, it becomes a spiral that goes around the pole an infinite number of revolutions, but its length to the pole is still finite. An oblique rhumb line has no well-defined direction at the pole.

M. C. Escher's woodcut Sphere Surface with Fish shows black and white fish swimming along eight rhumb lines of a sphere.

When a rhumb line is used by a 3D method in the Crs class, it is assumed that altitude varies linearly with horizontal distance between two nodes.

A truly straight line in 3D space. This line type is supported by Crs methods whose names end with "3D", and also by the methods Crs.route, Crs.azimuthFromLineSegment and Crs.pitchFromLineSegment. It is not supported by other Crs methods designed only for 2D calculations, but the footprint of a straight 3D line is very nearly a great-circle route, so the GreatCircle line type can be used instead. (The footprint would be a great-circle route if the earth were modelled as a sphere.)

Note that light rays and radio signals in the earth atmosphere do not follow a straight 3D line precisely, mainly due to atmospheric refraction that tends to bend the rays downwards.

A great-circle segment on the Earth ellipsoid is the shortest route between two points on the ellipsoid surface. It is also called an orthodrome, or a geodetic or geodesic route, or just a geodesic.

The "great-circle" term, which is borrowed from spherical geometry, cannot be taken literally on the ellipsoid, since the shortest route on an ellipsoid is usually not a circle, nor even an ellipse (you cannot construct it by cutting the ellipsoid with a plane).

When a great-circle segment is used by a 3D method in the Crs class, it is assumed that altitude varies linearly with horizontal distance between two nodes.

An approximate great circle. Some Crs methods can accept this line type, for faster but less accurate results.

A rhumb line, also called a loxodrome, is a curve with a constant bearing or azimuth: that is, it intersects each meridian with the same angle. It is not the shortest route on the ellipsoid, except if it is a meridian or the equator.

With older navigation systems, it was easier to split up a route into smaller rhumb-line segments. Modern systems can handle the continuously changing bearing of the great-circle route, but there is still a strong tradition of using rhumb lines in navigation to define waypoints etc.

A rhumb line looks straight on a MercatorProjection map. When an oblique rhumb line approaches a pole, it becomes a spiral that goes around the pole an infinite number of revolutions, but its length to the pole is still finite. An oblique rhumb line has no well-defined direction at the pole.

M. C. Escher's woodcut Sphere Surface with Fish shows black and white fish swimming along eight rhumb lines of a sphere.

When a rhumb line is used by a 3D method in the Crs class, it is assumed that altitude varies linearly with horizontal distance between two nodes.

A truly straight line in 3D space. This line type is supported by Crs methods whose names end with "3D", and also by the methods Crs.route, Crs.azimuthFromLineSegment and Crs.pitchFromLineSegment. It is not supported by other Crs methods designed only for 2D calculations, but the footprint of a straight 3D line is very nearly a great-circle route, so the GreatCircle line type can be used instead. (The footprint would be a great-circle route if the earth were modelled as a sphere.)

Note that light rays and radio signals in the earth atmosphere do not follow a straight 3D line precisely, mainly due to atmospheric refraction that tends to bend the rays downwards.