Predefined Ellipsoids

Programming with JViews Maps > Ellipsoid and Geodetic Datums > Ellipsoids > Predefined Ellipsoids

Predefined Ellipsoids

The IlvEllipsoidCollection class manages lists of predefined ellipsoids. A list of predefined ellipsoids, or kernel collection, can be retrieved using the method GetKernelCollection().

Ellipsoid collections are read from XML files containing the ellipsoid definitions. The Document Type Definition (DTD) for these definition files is:

<!DOCTYPE ellipsoid-list [
   <!ELEMENT ellipsoid EMPTY>
  <!ATTLIST ellipsoid
     a       CDATA   #IMPLIED
     b       CDATA   #IMPLIED
     invf    CDATA   #IMPLIED
     name    CDATA   #REQUIRED
     comment CDATA   #IMPLIED
  >

  <!ELEMENT ellipsoid-ref EMPTY>
  <!ATTLIST ellipsoid-ref
     ref     CDATA   #REQUIRED
     id      CDATA   #REQUIRED
  >

  <!ELEMENT ellipsoid-list (ellipsoid|ellipsoid-ref)* >
]>

In an ellipsoid definition file, you can find:

An ellipsoid

Defined either by its name, or its semi-major axis a and inverse flattening invf, or its semi-major axis a and semi-minor axis b.

An alias for an ellipsoid

Defined in the kernel collection of Maps. In case of alias, the required information is the id of the ellipsoid (the name to retrieve the ellipsoid) and the name of the ellipsoid in the kernel. When retrieving an alias ellipsoid from a collection, the ellipsoid is searched for using its id as a key, while the name of the returned ellipsoid is the one defined in the kernel collection.

The following XML file defines the Clarke 1880 ellipsoid, modified for IGN. This ellipsoid will be available as "Clarke 1880 (IGN)". Then you must set "WGS 1984" as an alias for the kernel "WGS 84" ellipsoid:

<ellipsoid-list>
  <ellipsoid name="Clarke 1880 (IGN)"
     comment="Clarke 1880 (Modified for IGN)"
     a="6378249.2"
     invf="293.4660213"
  />

  <ellipsoid-ref id="WGS 1984"
                 ref="WGS84"
  />

</ellipsoid-list>

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