SolidWorks generally has two sets of spline functions:
- The spline curve passes through the given points, i.e. spline fitting, (the curve S1 in the below figure)
- The given points are the control points of the spline curve, i.e. spline interpolation (the curve S2 in the below figure)
Accordingly, there are two functions which does the jobs:
- IModelDoc2.CreateSpline
- SketchManager.CreateSplinesByEqnParams
The below data are used in the experiments:
| int nOrder = 4; int nPoints = 5; |
| double[] Pt = new double[3 * nPoints]; Pt[0] = -0.1; Pt[1] = -0.1; Pt[2] = 0; Pt[3] = 0.1; Pt[4] = -0.1; Pt[5] = 0; Pt[6] = 0.1; Pt[7] = 0.1; Pt[8] = 0; Pt[9] = -0.1; Pt[10] = 0.1; Pt[11] = 0; Pt[12] = -0.15; Pt[13] = 0; Pt[14] = 0; |
For the 1st spline fitting problem, another point which is coincident to the 1st point should be appended, to indicate that this curve is closed:
| double[] Pt2 = new double[Pt.Length + 3]; Pt.CopyTo(Pt2, 0); Pt2[Pt.Length] = -0.1; Pt2[Pt.Length + 1] = -0.1; Pt2[Pt.Length + 2] = 0; modDoc.CreateSpline(Pt2); |
For the 2nd interpolation problem, the function call is a bit of cumbersome and the help manual is also less clear. After experimenting for a few times, here comes the solution.
- Prepare a kont vector, it could be uniform ones or whatever valid vector
| double[] pKnotsArray = new double[nOrder + nPoints]; for (int i = 0; i < pKnotsArray.Length; i++) pKnotsArray[i]=i; |
- According to the manual, prepare a property array, note that althought the parameters are integers, however
you must use a double array to hold the data, and later, this double array will be merged into one bigger double array:
| #region Property Array double[] PropertyArray = new double[4]; PropertyArray[0] = 3; //Dimension, 2 is not OK! PropertyArray[1] = nOrder; //Order PropertyArray[2] = nPoints; //Number of control Points PropertyArray[3] = 1; //Periodicity=true #endregion |
- Merge all the double array into a single double []:
|
int n1 = PropertyArray.Length; double [] Parameters=new double[n1+n2+n3]; |
modDoc.SketchManager.CreateSplinesByEqnParams(Parameters);
There are several notes to be mentioned:
- Even though the sketch is on a 2D plane, experiments show that the Z coordinates cannot be omitted;
- Even the spline curve is closed, it is no need to add another point (coincident with the 1st control point) to the control point list!
Otherwise, a sharp corner will result, as shown in the figure below. - I have also tried to use below codes, however in vein.
List<double []> Parameters=new List<double []>;
Parameter.Add(PropertyArray);
Parameter.Add(pKnotArray);
Parameter.Add(Pt);
modDoc.SketchManager.CreateSplinesByEqnParams(Parameters.ToArray()); -
The other function with the same name but different signature does not work in C# COM based programming,
since there is still no way to marshal an "int []" to a "ref int".
virtual SketchSegment ICreateSplineByEqnParams(ref int PropArray,
ref double KnotsArray,ref double CntrlPntCoordArray ); -
By adding another array W into the control point coordiate, the function CreateSplinesByEqnParams
can actually be used to model NURBS curve.
Posted in CAD, Dotnet/C#
