CassiniSoldnerProjection Class
An old-fashioned map projection.
NuGet/Assembly: Carmenta.Engine.5.16.2.nupkg (in the CECore assembly)
Syntax
public class CassiniSoldnerProjection : ProjectionRemarks
The Cassini-Soldner projection can be regarded as an Equidistant Cylindrical projection in transverse aspect (that is, the cylinder touches the earth along the central meridian). The scale is true along the central meridian, and along any great circle that is perpendicular to the central meridian.
This projection was popular before electronic computers were invented, since the projected coordinates are relatively simple to compute from longitude and latitude. However, once computed, the projected coordinates are hard to use for a surveyor who needs to compensate for local scale factors, since the projection is not conformal. So this projection is no longer popular, but it is still in use in some countries.
Some sources omit "Soldner" from the name, but other sources say that without Soldner, the projection has to use spherical formulas.
Accuracy
The projection formulas for CassiniSoldnerProjection use an ellipsoid model of the Earth. However, they are accurate only in a zone extending 3° to 4° from the central meridian. Farther away, the formulas are no longer internally consistent. We have tested some points with the Trinidad Grid:
distance from p to central meridian | distance from p to the result of unprojecting p to LongLat and then projecting it back again. |
|---|---|
3° | 0.01 m |
4° | 0.04 m |
5° | 0.13 m |
10° | 4.6 m |
20° | 196 m |
30° | 1932 m |
Since such differences can lead to all sorts of trouble, you should make sure that your application does not use a Cassini-Soldner projection too far away.
To display a world map in Cassini-Soldner, Carmenta Engine should be forced to use spherical formulas instead. There is no simple way to do it, since Cassini-Soldner is seldom wanted for a world map. However, if you associate your Cassini-Soldner projection with a new GeodeticDatum, whose ellipsoid has an inverseFlattening of 1.0e11 or greater, then the ellipsoid will be very nearly spherical, and spherical projection formulas will be used. (The datum shift for this spherical datum should be an IdentityDatumShift to some ordinary ellipsoidal datum, since the HelmertDatumShift class is not intended for spherical datums.)
Using this trick, we have produced the Cassini-Soldner world map below. The central meridian is 33°W, which gives a good way to present the Arctic Ocean as a small part of the Atlantic. Compare this map will the UtmProjection with the same central meridian.
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Inheritance Hierarchy
System.Object (not available in C#)
EngineObject
ResourceObject
Projection
CassiniSoldnerProjection
Platforms
Windows, Linux, Android
CassiniSoldnerProjection Members
The CassiniSoldnerProjection type has the following members.
Constructors
| Name | Description |
|---|---|
| CassiniSoldnerProjection | Creates a new Cassini-Soldner projection. |
Properties
| Name | Description |
|---|---|
| Authority | Gets the name of an authority, which is often "epsg". Inherited from Projection |
| AuthorityCode | Gets the unique code for the projection instance, according to the Authority, for example "19883". Inherited from Projection |
| CentralLatitude | Gets the central latitude, also known as latitude of origin. |
| CentralLongitude | Gets the central longitude, also known as central meridian or longitude of origin. |
| FalseEasting | Gets the offset added to the projected x coordinates (the eastings). |
| FalseNorthing | Gets the offset added to the projected y coordinates (the northings). |
| IsDisposed | Gets a value that tells whether the current CassiniSoldnerProjection has been disposed. Inherited from EngineObject |
| LengthUnit | Gets the length unit of the projected coordinates. |
 LongLat | Gets a pre-defined LongLatProjection instance. Inherited from Projection |
| Name | Gets or sets the name of the CassiniSoldnerProjection. Inherited from ResourceObject |
| NativeHandle | Gets the native Carmenta Engine kernel object the current CassiniSoldnerProjection represents. Inherited from EngineObject |
| IUserProperties.UserProperties | Gets the AttributeSet that contains the user properties. Inherited from IUserProperties |
Methods
| Name | Description |
|---|---|
| Clone | Creates a copy of an object. Inherited from EngineObject |
| Dispose | Releases the reference to the native Carmenta Engine kernel instance the EngineObject represents. Inherited from EngineObject |
| Equals | Determines whether this instance is equal to another. Inherited from EngineObject |
| Utm | Returns one of the 120 predefined instances of Universal Transverse Mercator. Inherited from Projection |