Boundary line of a flat object

onrender · April 25, 2018, 6:37am

Hi,

I am thinking how to find the boundary line of a flat object that includes splines, semicircle and lines.
It could be easy in case of a polygonal object by selecting grips but for curves I have no idea.

I can also evaluate the curves and simplify it by some points on the curve and then connect it but there might other way.

Can anybody suggest how to do it?

tom_makin · April 25, 2018, 11:03am

Can you give an example of the geometry?

And what tools are you hoping to use to extract the boundary? e.g. PythonScript, RhinoCommon Plugin, Grasshopper?

onrender · April 25, 2018, 10:10pm

Thanks, it is like in the picture. This will be the duplicate surfaceBorder

tom_makin · April 26, 2018, 8:14am

Cool, this script should help get you started.

github.com

mcneel/rhinocommon/blob/master/examples/py/ex_dupborder.py

import Rhino
import scriptcontext

def DupBorder():
    filter = Rhino.DocObjects.ObjectType.Surface | Rhino.DocObjects.ObjectType.PolysrfFilter
    rc, objref = Rhino.Input.RhinoGet.GetOneObject("Select surface or polysurface", False, filter)
    if rc != Rhino.Commands.Result.Success: return rc

    rhobj = objref.Object()
    brep = objref.Brep()
    if not rhobj or not brep: return Rhino.Commands.Result.Failure
    rhobj.Select(False)
    curves = brep.DuplicateEdgeCurves(True)
    tol = scriptcontext.doc.ModelAbsoluteTolerance * 2.1
    curves = Rhino.Geometry.Curve.JoinCurves(curves, tol)
    for curve in curves:
        id = scriptcontext.doc.Objects.AddCurve(curve)
        scriptcontext.doc.Objects.Select(id)
    scriptcontext.doc.Views.Redraw()
    return Rhino.Commands.Result.Success

This file has been truncated. show original

This is a python script, but you could translate the principles to a RhinoCommon plugin if needs. Let me know if you need help modifying it to fit your use case.

onrender · April 26, 2018, 8:54pm

Thank you Tom. The method works just fine.