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RhinoScript – Self-Intersecting Surface

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  • 7. QED (Oct 24, 2009 23.00):

    Hi Hanno,

    Yes! This is the solution. Whenever the surface intersects itself the offset surface intersects with the original one. I did not run it for a 1000 tests but it does seems to be foolproof so far.
    Thanks!

    Regards,

    Dirk


    'SurfaceSelfIntersectingCheck = Sub SSinC()
    'QED - 23/10/2009
    '--------------------------------------------

    Call SSinC()
    Sub SSinC()
     
    Dim arrSelect
    Dim strSurfaceA, strSurfaceB, arrSSinC

    'selects existing surface
    arrSelect = Rhino.ObjectsByType(8, True)
    If IsArray(arrSelect) Then
    strSurfaceA = arrSelect(0)
    End If

    'creates offset surface at 10 units
    strSurfaceB = Rhino.OffsetSurface(strSurfaceA, 10)

    'checks for intersection between both surfaces
    arrSSinC = Rhino.SurfaceSurfaceIntersection(strSurfaceA, strSurfaceB,, True)

    'the array is empty: the surfaces do not intersect
    If Not IsArray(arrSSinC) Then
    Rhino.Print "Good Surface does not intersect with itself!"
    Rhino.DeleteObject (strSurfaceB)
    Rhino.UnselectAllObjects
    Exit Sub
    End If

    'the array is not empty: the surfaces intersect
    Rhino.Print "Bad Surface with SelfInterSecting problems!!!."
    Rhino.DeleteObject (strSurfaceB)
    Rhino.UnselectAllObjects

    'Deletes unwanted curves which are created
    Dim arrCurves
    arrCurves = Rhino.ObjectsByType(4, True)
    Rhino.DeleteObjects (arrCurves)

    End Sub

  • 6. Hanno (Oct 21, 2009 09.51):

    Hi Dirk,

    you are of course right. The isocurves don't self-intersect at all, there I didn't quite think it to the end :-)
    What you could do is offset your surface in a rather small distance and check if the offset surface and the original one intersect. This way you automatically get a kind of safety margin that you can control by the offset distance.
    But directly limiting the control point distribution at design time is still a more reasonyble approach, if you don't limit yourself too much with that.

    Hanno

  • 5. QED (Oct 20, 2009 17.01):

    Hi Hanno,

    Thanks again!
    I manually played around a little bit with those IsoCurves, but they do not seem to intersect themselves, they curl in 3D space (see jpg). However, I still do have to script a test to be absolutely sure I cannot use this strategy. So, I will overwrite some of the randomly generated xyz-coordenates with fixed numbers. This way I can reasonable control the surface.

    Regards,

    Dirk

  • 4. Hanno (Oct 19, 2009 09.40):

    Hi Dirk,

    another idea: maybe you could use ExtractIsoCurve to iterate through your surfaces and check these isocurves for self-intersection. Given a rather small step size between your test curves, this should be a good indicator.

    Regards

    Hanno

  • 3. QED (Oct 19, 2009 02.23):

    Hi Hanno,

    Thanks for your reply.
    Some command like "SurfaceIntersection" is what I need, but does not exist. I could not find anything else which would give me an indication about "intersecting", but I am not in NURBS-math.

    I empirically checked on the coordinates of the control points, as you suggested. I run the script some 150 times, but I could not detect any significance in the values of the xyz-coordinates of the control points, between "bad" and "good" surfaces (or maybe I could not see/understand if something was "different").
    I tried with "area" of the surface, since I noticed that most of the "bad" surfaces were smaller. But it is not fool proof. Some of the "bad" surfaces are bigger than "good" ones, although a great part of the "bad" ones can be eliminated this way.

    Regards,
    Dirk

  • 2. Hanno (Oct 17, 2009 12.42):

    Hi,

    in my experience, surface analysis via script is a rather complex thing. For curves you can simply use CurveCurveIntersection to check for self-intersections, but that does not work for surfaces. There are also some validation commands like "check" in rhino, but they do not include self-intersetions.
    In your case, maybe you could come up with a control point based approach, checking their positions and discarding surfaces that do not match some criteria?
    If you find out something, I would be glad to hear from you!

    Regards

    Hanno

  • 1. QED (Oct 15, 2009 16.05):

    Hi All,
    I am working on a script which creates new surfaces (p.e. 100 variations) by randomly changing the coordinates of the control points of a simple nurbs surface. Some of the surfaces created, however "fold" through themselves which makes them useless for further exploration. I can visually check the surfaces and manually delete them. I can also reorganize the coordinates of the control points by script, but then resulting surfaces are very similar. I do not find apparently any different value (analyse-definition-list) which I could use to classify the surfaces. Any suggestions how I can detect a "useless" self-intersecting surface?

    Thanks!
    Dirk

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