How to solve the "Curve.CreateBooleanDifference" creating more unwanted curves?

Grasshopper
1

Hi guys,
My goals:1.Red boundaries;2.Short time;(Picture-00,Picture-01)
My problems:1.Emtpy results;2.Missing wanted curves;3.Result include unwanted curves.(Picture-02,Picture-03,Picture-04,Picture-05)
Firstly,I wish to get the curve boundaries inside of the CrvBase which is showen as red area on picture-01.

Picture0
Picture0669×546 14.7 KB
Picture1
Picture1652×563 17.9 KB

Secondly,I want the whole operation consume time as short as possible.
My codes with Will_wang’s help for Case A and B:

Curve[] Union_Crvs = Curve.CreateBooleanUnion(ListCrvs, 1.0);
Curve[] Dif_Crvs = Curve.CreateBooleanDifference(CrvBase, Union_Crvs, 1.0);
List<Curve> LCrv = new List<Curve>();
foreach(Curve iCrv in Dif_Crvs)
{
  Point3d iCenPt = Rhino.Geometry.AreaMassProperties.Compute(iCrv).Centroid;
  Rhino.Geometry.PointContainment PtCont = CrvBase.Contains(iCenPt, Plane.WorldXY, 0);
  if(Convert.ToInt32(PtCont) == 1){LCrv.Add(iCrv);}
}
A = LCrv;

Unfortunately,problems have happened.
Case A (CrvBase is a convex curve):
When angle is between 4.64 and 4.67,the results are empty.But the ListCrvs obviously overlap on CrvBase.(picture-2)

Picture2
Picture21776×569 77.1 KB

When angle is 4.79,the results lost some curves.(picture-03)
Picture3
Picture31669×610 111 KB

Case B (CrvBase is a concave curve):
When anlge is between 1.78 and 1.87,the results show an unwanted curve outside CrvBase as a “wanted” one.(picture-04)
Picture4
Picture41703×541 66.7 KB

"Centroid " method will not sort it out.
Codes for Case C:
Although I fix the “unwanted” problem,it cost much more time.

Curve[] Union_CrvsTmp = Curve.CreateBooleanUnion(ListCrvs, 0.1);
Curve[] Union_Crvs = Curve.CreateBooleanUnion(Union_CrvsTmp, 0.1);
Curve[] Dif_Crvs = Curve.CreateBooleanDifference(CrvBase, Union_Crvs, 0.1);//find all possible curves
List<Curve> LCrv = new List<Curve>();
if(Dif_Crvs.Length != 1)
{
  List<Curve> Select_Crvs = new List<Curve>();
  List<Curve> Remove_Crvs = new List<Curve>();
  for(int i = 0;i < Dif_Crvs.Length;i++)
  {
    //Inside the CrvBase，IsetCrv.Length != 0
    Curve[] IsetCrv = Curve.CreateBooleanIntersection(Dif_Crvs[i], CrvBase, 0.1);
    if(IsetCrv.Length != 0){Select_Crvs.Add(Dif_Crvs[i]);}
    for(int j = 0;j < Union_Crvs.Length;j++)
    {
      //find the curves outside of the CrvBase,store their indexes
      Curve[] IsetPRBs = Curve.CreateBooleanIntersection(Dif_Crvs[i], Union_Crvs[j], 0.1);
      if(IsetPRBs.Length != 0){Remove_Crvs.Add(Dif_Crvs[i]);}
    }
  }
  LCrv = Select_Crvs.Except(Remove_Crvs).ToList();//remove the outside ones
}
else{LCrv = new List<Curve>(Dif_Crvs);}
A = LCrv;

Case C (CrvBase is a concave curve):
Unluckily,when anlge is between 3.35 and 4.09,the results also lost some curves.(picture-05)

Picture5
Picture51742×467 77.4 KB

Could anybody help me to solve my 3 problems?I attach relevant documents.
Question.3dm (41.7 KB) Question.gh (15.1 KB)

2

for starters, you can test Curve.Contains()
somehow get a centroid-like point and exclude those outside of your “CrvBase”
only works for close curves obviously…

3

Thank you for your suggestion.I successfully select the inside curves.But it still cost much time.Is there any methods to save time?

    Curve[] Union_Crvs = Curve.CreateBooleanUnion(ListCrvs, 1.0);
    Curve[] Union_UnCrvs = Curve.CreateBooleanUnion(Union_Crvs, 1.0);
    Curve[] Dif_Crvs = Curve.CreateBooleanDifference(CrvBase, Union_UnCrvs, 1.0);    
    List<Curve> LCrv = new List<Curve>();
    foreach(Curve iCrv in Dif_Crvs)
    {
      Point3d iCenPt = Rhino.Geometry.AreaMassProperties.Compute(iCrv).Centroid;
      Rhino.Geometry.PointContainment PtCont = CrvBase.Contains(iCenPt, Plane.WorldXY, 0.01);      
      if(Convert.ToInt32(PtCont) == 1){LCrv.Add(iCrv);}
    }
    A = LCrv;
4

Here is a solution, although it still doesn’t help you reduce computing time.

  private void RunScript(Curve H, List<Curve> S, ref object A)
  {
    double tol = RhinoDoc.ActiveDoc.ModelAbsoluteTolerance;
    Curve[] u = Curve.CreateBooleanUnion(S, tol);
    var rd = nic.Components.FindComponent("RegionDifference");
    object[] args = new object[]{H, u, Plane.WorldXY};
    // you can change the world xy to your curve plane
    string[] msg;
    var results = rd.Evaluate(args, false, out msg);
    A = results[0];
  }

remember to add this reference at the top
using nic = Rhino.NodeInCode;

image
image780×493 55.1 KB

2 Likes
5

Thanks a lot ! Your method fixes out the “Red boundaries”.I am trying to reduce time with multi-threading.

6

Hi Will,
I finally find that the key factor in these problems is the “tolerance”(Curve.CreateBooleanDifference(curveA,curveB,tolerance)).When tolerance is as small as possible,“empty results” and “Missing wanted curves” can be sorted out.Using “RegionDifference” is truely a bright way.Thank you all the same.