How to "elegantly" match BrepFace normal with surface face direction?

Rhino Developer
1

So Curve.OffsetNormalToSurface() is offsetting consistently to one side and not following random surface U,Vs?

2

Hi @Asterisk,

Curve.OffsetNormalToSurface works with surfaces. If you pass it a Brep face, it will just evaluate the face’s underlying surface.

– Dale

3

image
image1180Ă—764 8.42 KB

offset = edge.OffsetNormalToSurface(brepface, -off) # note negative offset to offset opposite of normal

Where brepface is:
image

Result:

image
image1153Ă—787 3.93 KB

After flipping U and V:

image
image1155Ă—763 8.14 KB

image
image949Ă—856 3.35 KB

Same results if I do

offset = edge.OffsetNormalToSurface(face.ToNurbsSurface(), -off)

Is it a bug? I need U,Vs to not matter. Or “fix” 'em to match surface face orientation with a couple of code lines if possible. @dale

4

Sorry if I revive this old topic.

did you find a workaround for that one? I’m bumping in the exact same problem.

Curve.OffsetNormalToSurface(...

doesn’t seem to make a difference between v(0,0,1) and v(0,0,-1) as output.
If I flip the surface, the offsetted crv would stay in the same place.

I then made this:

public Curve OffsetNormal(Surface S, Curve C, double D)
  {
    Point3d cCenter = C.GetBoundingBox(true).Center;
    double u,v = 0.0;
    S.ClosestPoint(cCenter, out u, out v);
    Vector3d normal = S.NormalAt(u, v);
    normal.Unitize();
    C.Transform(Transform.Translation(normal * D));
    return C;
  }

which would give me the same result.

how would i access the “real” direction without being forced to do both directions and compare them.

5

please notice that the brepface and the surface can have reversed normals. you can check this by

https://developer.rhino3d.com/api/RhinoCommon/html/P_Rhino_Geometry_BrepFace_OrientationIsReversed.htm

does this help ? kind regards -tom

6

I solved it by not using edge.OffsetNormalToSurface()

            brepoff = Rhino.Geometry.Brep.CreateFromOffsetFace(face, -offset, 0.001, False, False)
            dist = abs(offset) + 1
            
            for i in brepoff.Edges:
                tstPt = i.PointAt(i.NormalizedLengthParameter(0.5)[1])
                chk = round(refpt.DistanceTo(tstPt), 3)
                if chk < dist: edgeoff, dist = i, chk
            
            newflange = Rhino.Geometry.Brep.CreateFromLoft(
                [edge, edgeoff],
                Rhino.Geometry.Point3d.Unset,
                Rhino.Geometry.Point3d.Unset,
                Rhino.Geometry.LoftType.Straight,
                False)[0]
7

Thank you, this did it!

8

Thank you both, guys. I came to the same conclusion, but was too tired yesterday to finish the workaround. Thanks!!