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problem with get spline params

Question asked by Moon Wang on Apr 16, 2018
Latest reply on Apr 18, 2018 by Moon Wang

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Hello,everyone.I am now having some poblem with the Api function GetBCurveParams,I want to extract the params of a spline after I have sktched in Solidworks before.Because the skecth is drawed by myself,so I know the coordinates of the spline's control points.However，I have test the api GetBCurveParams(false/true),GetBCurveParams3(true,false/true,false/true),GetBCurveParams4(true,false,false,false)to get the control points and knot vector in cubic curve ,none of them can accurately does well.For eample,I drew the spline with 9 control points ,by SplineArray4 = swCurve.GetBCurveParams4(true, false, true, false);I get the array which gives back me 6 control points ,or the knot vector only consists of 0 and 1.I am really puzzled.Can someone give me some hints,thank you

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Taus Moller Apr 16, 2018 9:18 AM
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Posting you example would help diagnose the problem. However i have had issues with this in the past. One thing to note is that when drawing a spline in solidworks you are note actually placing Controls points, but rather points for the spline to pass through. Try right clicking on the spline and select "Display Control Polygon" this will show you the actual control points. This might give you a hint to what is going on
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- Moon Wang @ Taus Moller on Apr 16, 2018 10:01 AM
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  So you can see that I am really should get the control points, and I have already set their coordinates
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  - Jacob Corder @ Moon Wang on Apr 16, 2018 10:45 AM
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    2018 SOLIDWORKS API Help - GetSplineHandles Method (ISketchSpline)
    2018 SOLIDWORKS API Help - Get and Set Spline Handles Example (VBA)
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    - Moon Wang @ Jacob Corder on Apr 16, 2018 8:33 PM
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      CODE:
      
      object[] skSegments = (object[])swSketch.GetSketchSegments();
      for (int t = 0; t < SegNum; t++)
                              {
                                  SketchSegment iSketchSegmengt;
      int sketchType = iSketchSegmengt.GetType();
                                  if (sketchType == (int)swSketchSegments_e.swSketchSPLINE)
                                  {
                                     ISketchSpline swSketchSpline;
                                      swSketchSpline = (ISketchSpline)iSketchSegmengt;
                                      ICurve swCurve;
                                      swCurve = iSketchSegmengt.IGetCurve();
                                      int size=swCurve.IGetBCurveParamsSize(false);
                                      double[] SplineArray = new double[size];
                                      SplineArray=swCurve.GetBCurveParams(true);
      }
      }
      /////////////////////////////
      I don't think that I need get SplineHandles(),don't you think so?
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      - Taus Moller @ Moon Wang on Apr 18, 2018 5:00 AM
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        You are using and obsolete version of GetBCurveParams. If you check the documentation (GetBCurveParams) you will see that it directs you to another method you should use. In fact it has been deprecate a few times. The current one is GetBCurveParams5.
        
        Note it returns an ISplineParam you can query for the datapoints.
        
        something like this will do the trick:
        ICurve swCurve; swCurve = seg.IGetCurve(); ISplineParamData SplineParams = swCurve.GetBCurveParams5(true,false,false,false); int numpoint = SplineParams.ControlPointsCount; object opoints = new double[numpoint*3]; SplineParams.GetControlPoints(out opoints); double[] point = (double[])opoints;
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        Moon Wang @ Taus Moller on Apr 17, 2018 9:44 PM
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        Thank you for your advice.I have test it,but it turns out that the result is same as before,athough the form of the returned array has changed .If I use swCurve.GetBCurveParams5(true,false,false/true,false), the control points has 6 points,the knot vector has 10 member (0,0,0,0,0.5,0.5,1,1,1,1),If I use swCurve.GetBCurveParams5(true,true,tue,false),the control points has 14 points,knot vector has 18 member.So I think maybe Solidworks api cannot give us right answer....
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        Taus Moller @ Moon Wang on Apr 18, 2018 5:05 AM
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        I am getting the expected result from GetBCurveParams5. I.e. drawing a style spline with 10 points i get a 30 point array from the ISplineCurveData. I suspect the issue is in the part. If you could post the Solidworks part it would help a lot.
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        Moon Wang @ Taus Moller on Apr 18, 2018 8:50 AM
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        Taus,
        Thank you very much for your testing, I am posting the sldprt(Solidworks 2015) and igs file of the Solidworks part, I appricate your help very much.
                 Some of my codes is below:
                                     ICurve swCurve;
                                        swCurve = iSketchSegmengt.IGetCurve();
        
                                        ISplineParamData SplineData=null;
                                        SplineData = (ISplineParamData)swCurve.GetBCurveParams5(true,false,true,false);
                                        int ConNum = SplineData.ControlPointsCount;
                                        int KnotNum = SplineData.KnotPointsCount;
                                        //double []ConPoints=new double[ConNum];
                                        object uConPoints;
                                       // double iConPoints;
                                        object uKontVector;
                                        //object[] KontVector = new object[KnotNum];
                                        SplineData.GetControlPoints(out uConPoints);
                                        //SplineData.IGetControlPoints(ConNum, out iConPoints);
                                        SplineData.GetKnotPoints(out uKontVector);
        
                                        int size3 = swCurve.IGetBCurveParamsSize3(true, false, false);
                                        double[] SplineArray3 = new double[size3];
                                        SplineArray3 = swCurve.GetBCurveParams4(true, false, false, false);
        Attachments
        BsplineTest.IGS.zip5.5 KB
        BsplineTest.SLDPRT.zip58.5 KB
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        Taus Moller @ Moon Wang on Apr 18, 2018 11:10 AM
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        A bit of experimentation gave some quite confusing results for me. I tried deleting everything but the spline in question and to see what the result would be. I got a similar result to you.
        
        Then i tried creating a new style spline to see if it displayed the same behavior. This one returned the expected number of control points at first. However i found that moving around the control points of the spline would change the number of points returned by SplineParamData.GetControlPoints.
        
        My best guess is that Solidworks tries to provide some "user friendly" handles that look like control points but does some secret stuff underneath. I would try to contat API support with the issue, as GetBCurveParams5 certainly does not behave as one would expect
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        Moon Wang @ Taus Moller on Apr 18, 2018 9:15 PM
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        Ok，so the result turns out like this,I am also waiting for the reply from API support.Thank you very much,I will test it later until find the reason....
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problem with get spline params

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