Description
This azimuthal projection uses the center of the earth as its perspective point. All great circles are straight lines, regardless of the aspect. This is a useful projection for navigation because great circles highlight routes with the shortest distance.
Projection method
This is a planar perspective projection viewed from the center of the globe. The projection can be any aspect.
Point of tangency
A single point anywhere on the globe.
Polar aspect—North Pole or South Pole.
Equatorial aspect—any point along the equator.
Oblique aspect—any other point.
Linear graticules
All meridians and the equator.
Properties
Shape
Increasingly distorted from the center; moderate distortion within 30 degrees of the center point.
Area
Distortion increases with distance from the center; moderate distortion within a 30 degree radius of the center.
Direction
Accurate from the center.
Distance
No line has an accurate scale, and the amount of distortion increases with distance from the center.
Scalar distortion for polar aspect
| Degrees from center (°) | Meridian distortion (%) | Latitude distortion (%) |
|---|---|---|
15.0 | 7.2 | 3.5 |
30.0 | 33.3 | 15.5 |
45.0 | 100.0 | 41.4 |
60.0 | 300.0 | 100.0 |
Limitations
This projection is limited by its perspective point and cannot project a line that is 90° or more from the center point; this means that the equatorial aspect cannot project the poles, and the polar aspects cannot project the equator.
A radius of 30° produces moderate distortion, as indicated in the table above. This projection should not be used more than about 60° from the center.
Uses and applications
All aspects—routes of navigation for sea and air.
Polar aspect—navigational maps of polar regions.
Equatorial aspect—navigational maps of Africa and the tropical region of South America.
Parameters
Desktop
- False Easting
- False Northing
- Longitude of Center
- Latitude of Center
Gnomonic Auxiliary Sphere (Desktop version 9.3 and later)
- False Easting
- False Northing
- Longitude of Center
- Latitude of Center
- Auxiliary Sphere Type
Workstation
- Radius of the sphere of reference
- Longitude of center of projection
- Latitude of center of projection
- False Easting (meters)
- False Northing (meters)