PrimeMeridian Class
The meridian whose longitude is zero, usually Greenwich.
NuGet/Assembly: Carmenta.Engine.5.16.2.nupkg (in the CECore assembly)
Syntax
public class PrimeMeridian : ResourceObjectRemarks
A PrimeMeridian object must be attached to a GeodeticDatum, which is attached to a Crs; see the class diagram.
When coordinates are expressed in longitude and latitude, it is easy to agree where the equator should be (since the earth is rotating). But the choice of prime meridian, where the longitude is defined to be zero, is quite arbitrary. In the 1800s and earlier, many countries used a prime meridian through their capital for national mapping. The Ferro meridian, going through the westmost of the Canary Islands (now known as El Hierro), was suggested as an international prime meridian by France in 1634, since it would give (most) locations in the Old World a positive longitude. The Ferro meridian became popular in European mapping, but since it was defined to be exactly 20 degrees west of the Paris meridian, the Englishmen regarded it as the Paris meridian in disguise, and continued to use the Greenwich meridian. At the International Meridian Conference in 1884, twenty-five nations agreed to use Greenwich as the international prime meridian. But the vote was not unanimous, and to this day the maps of some countries use a prime meridian that differs from Greenwich (and from Ferro).
If a coordinate reference system uses the Projection.LongLat, then it is important to use the correct PrimeMeridian in the GeodeticDatum. But if the coordinate reference system uses a national projection that is formally based on a non-Greenwich prime meridian, then you must decide how to represent it:
You can follow the national definition, and use the non-Greenwich prime meridian. Then, the central longitude should be expressed relative to this prime meridian.
You can normalize the national definition to use Greenwich instead. Then, the central longitude should be expressed relative to Greenwich.
If the application has to export the Crs to some common format, like Well-Known Text, we recommend using the Greenwich-based variant of the Crs, since that is less likely to cause interoperability problems.
In Carmenta Engine itself, the two choices are equivalent in most situations, but the difference can be noticed if the application calls the methods Crs.ProjectFromLongLat and Crs.UnprojectToLongLat. This is one reason why the Crs.ProjectTo methods are recommended as more robust and easier to understand.
Inheritance Hierarchy
System.Object (not available in C#)
EngineObject
ResourceObject
PrimeMeridian
Platforms
Windows, Linux, Android
PrimeMeridian Members
The PrimeMeridian type has the following members.
Constructors
| Name | Description |
|---|---|
| PrimeMeridian | Creates a new PrimeMeridian. |
Properties
| Name | Description |
|---|---|
 Athens | Gets the predefined prime meridian for Athens. |
| Bern | Gets the predefined prime meridian for Bern. |
| Bogota | Gets the predefined prime meridian for Bogota. |
| Brussels | Gets the predefined prime meridian for Brussels. |
| FerroAlbrecht | Gets a predefined prime meridian for Ferro, using Theodor Albrecht's value for the longitude from Greenwich. |
| FerroRounded | Gets a predefined prime meridian for Ferro, using a rounded longitude from Greenwich. |
| Greenwich | Gets the predefined prime meridian for Greenwich. |
| IsDisposed | Gets a value that tells whether the current PrimeMeridian has been disposed. Inherited from EngineObject |
| Jakarta | Gets the predefined prime meridian for Jakarta. |
| Lisbon | Gets the predefined prime meridian for Lisbon. |
| LongitudeFromGreenwich | Gets the longitude from Greenwich, in degrees (positive east). |
| Madrid | Gets the predefined prime meridian for Madrid. |
| Name | Gets or sets the name of the PrimeMeridian. Inherited from ResourceObject |
| NativeHandle | Gets the native Carmenta Engine kernel object the current PrimeMeridian represents. Inherited from EngineObject |
| Oslo | Gets the predefined prime meridian for Oslo. |
| Paris | Gets a predefined prime meridian for Paris, based on French sources. |
| Rome | Gets the predefined prime meridian for Rome. |
| Stockholm | Gets the predefined prime meridian for Stockholm. |
| 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 |