AcDbSpline

Class Hierarchy

AcRxObject
    AcGiDrawable
    AcHeapOperators
        AcDbObject
            AcDbEntity
                AcDbCurve
                    AcDbSpline
                        AcDbHelix

C++

class AcDbSpline : public AcDbCurve;

File

dbspline.h

Description

This class implements the AutoCAD SPLINE entity.

Objects of the AcDbSpline class use an embedded gelib object to maintain the actual spline information. The spline itself may either be a simple curve fit (within a specified tolerance which may be 0) through a set of "fit points," or it may be a NURBS spline (that is, a set of control points, knots, and weights used to define the spline path). Internally, a curve-fit spline still has NURBS data; however the reverse is not true.

The following books are a good place to start to get a basic understanding of spline curves:

Curves and Surfaces for CAGD by Gerald Farin
Mathematical Elements for Computer Graphics by David Rogers and Alan Adams
An Introduction To Splines For Use In Computer Graphics & Geometric Modeling by Richard H. Bartels, John C. Beatty, and Brian A Barsky

Remarks

The AcDbSpline class provides functions to query and set a curve-fit spline and a set of functions to query and set a NURBS spline. It is not recommended that the curve fit functions be called on a NURBS spline or that the NURBS functions be called on a curve fit spline. Invalid data, or worse, may result. The AcDbSpline::hasFitData() method can be used to determine which type of spline is in hand.

Creating a NURBS spline with a sequential series of identical control points results in an unusable spline due to continuity problems.

Links

AcDbSpline Constructor, AcDbSpline Methods