API Reference > imodeljs-common > Geometry > HorizontalCRSProps > ellipsoid ellipsoid ellipsoid: undefined | GeodeticEllipsoidProps The complete definition of the geodetic datum referred to by datumId. It can also be used if the datum is not stored in either service or dictionary Defined in core/common/src/geometry/CoordinateReferenceSystem.ts Line 110 Last Updated: 12 June, 2024