The geometry of an Alignment, Parcel, or PlanFeature makes use of a CoordGeom element to store a part of its geometry. A CoordGeom element consists of any number of linear elements or curve/spiral elements.
The LandXML Reader currently has limited support for Curve and Spiral elements. Curve elements which are arc types, defined by three points (start, center, end) will be read. Chord Curve elements are not read, and no Spiral elements are read. If a Curve or spiral type is not read it will result in an interpolation between segments of a CoordGeom element. A warning will be issued if a spiral element or an unsupported Curve element is encountered. Support for these elements will be added in future versions of the reader.
It is recommended that if the data contains a spiral or curve element as part of a CoordGeom element that the geometry of the output be considered faulty (since when a spiral or curve is skipped, the intervening space will be linearly interpolated from the surrounding segments). But if linear interpolation produced correct geometry, then there would have been no need for a curve or spiral component.