SphereRadiusSource Enumeration
Specifies how the sphere radius is determined, for a map projection using spherical formulas.
NuGet/Assembly: Carmenta.Engine.5.16.2.nupkg (in the CECore assembly)
Syntax
public enum SphereRadiusSourceValues
| Value name | Value | Description |
|---|---|---|
| EquatorialRadius | 0 | The sphere radius equals the equatorial radius of the ellipsoid. |
| MeanRadiusOfCurvatureAtStandardParallel | 1 | The sphere radius is the mean radius of curvature, at the standard parallel, on the ellipsoid. |
| MeanRadiusOfCurvatureAtCentralLatitude | 2 | The sphere radius is the mean radius of curvature, at the central latitude, on the ellipsoid. |
| EqualArea | 3 | Use the radius of the sphere that has the same surface area as the ellipsoid. |
| RadiusFromArgument | 4 | The sphere radius is explicitly given as an argument to the projection constructor. |
Remarks
When using spherical map projection formulas just to display data, the exact choice of sphere radius is not important. But when reading geodata stored in a spherical map projection, it is important to reproduce the sphere radius that was used by the data provider, in order to interpret the geodata correctly.
The RadiusFromArgument can always be used, and is simplest to understand.
Each of the other choices represents a common rule of thumb that derives a reasonable sphere radius from the reference ellipsoid. (Remember that a Projection is always used as a part of a Crs, which has a GeodeticDatum, which has a reference Ellipsoid.)
The EquatorialRadius is used in the predefined Crs.Wgs84MercatorWeb. It is also the default choice.
The EqualArea is generally useful, but some sources recommend it only for equal-area map projections.
When the mean radius of curvature is mentioned above, the radius of curvature of the ellipsoid will be computed at a single point at the specified latitude, but since the radius of curvature varies with the direction (azimuth) from the point, the result is averaged over all directions. The latitude can be specified as the standard parallel only in the EquidistantCylindricalProjection. The mean radius of curvature, either on the standard parallel or the central latitude, is recommended by EPSG except for equal-area projections.
Platforms
Windows, Linux, Android