public double SpheroidSemiMajorAxis {get;}

// Get datum of a spatial reference
SpatialReference srWgs84 = SpatialReferences.WGS84;
Datum datum = srWgs84.Datum;
// datum.Name = "D_WGS_1984"
// datum.Wkid = 6326
// datum.SpheroidName = "WGS_1984"
// datum.SpheroidWkid = 7030
// datum.SpheroidFlattening = 0.0033528106647474805
// datum.SpheroidSemiMajorAxis = 6378137.0
// datum.SpheroidSemiMinorAxis = 6356752.3142451793

// Custom WKT
string wyomingWkt = "PROJCS[\"Wyoming_State_Pl_NAD_1927\",GEOGCS[\"GCS_North_American_1927\",DATUM[\"D_North_American_1927_Perry\",SPHEROID[\"Clarke_1866_Chase\",6378210.0,250.0]],PRIMEM[\"Greenwich\",0.0],UNIT[\"Degree\",0.0174532925199433]],PROJECTION[\"Transverse_Mercator\"],PARAMETER[\"false_easting\",500000.0],PARAMETER[\"false_northing\",0.0],PARAMETER[\"central_meridian\",-107.3333333],PARAMETER[\"scale_factor\",0.9999412],PARAMETER[\"latitude_of_origin\",40.66666667],UNIT[\"Foot_US\",0.3048006096012192]]";
SpatialReference srFromWkt = SpatialReferenceBuilder.CreateSpatialReference(wyomingWkt);
datum = srWgs84.Datum;
// datum.Name = "D_North_American_1927_Perry"
// datum.Wkid = 0
// datum.SpheroidName = "Clarke_1866_Chase"
// datum.SpheroidWkid = 0
// datum.SpheroidFlattening = 0.004
// datum.SpheroidSemiMajorAxis = 6378210.0
// datum.SpheroidSemiMinorAxis = 6352697.16