实体定义
几何（GfcGeometry），所有几何对象的基类。
继承关系
GfcRoot
└GfcGeometry
├
GfcVector2d
├
GfcVector3d
├
GfcIntervald
├
GfcCoordinates3d
├
GfcCoordinates2d
├
GfcBox3d
├
GfcBody
├
GfcCurve2d
├
GfcCurve3d
├
GfcSurface
├
GfcTopology
└
GfcMatrix