Curvature Graph - RhinoCommon

Rhino Developer
1

Hi,

I would like to ask about curvature graphs in grasshopper component

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Is there any rhinocommon method that could do the same display?
I was thinking that the values of vectors are osculating circle radius, but they are not.

@AndersDeleuran for bending rods and kangaroo you were displaying these graphs.
Could you share the code regarding this issue? :slight_smile:

Or is it display of second derivative of a curve?

2

I certainly can. Though mine was operating on bendy polylines of course, so I’m not sure if that would help much?

Edit: Here’s the method extracted from the larger bendy beam analysis class:

    def __calculateBendingRadii(self,polyline,roundDecimal,maxCircleRadius,minCircleRadius):
        
        """
        Calculate the local bending radius for each vertex of a polyline.
        """
        
        # Return lists
        radii = []
        planes = []
        circles = []
        
        # Cast to polyline
        if type(polyline) is not rc.Geometry.Polyline:
            polyline = polyline.TryGetPolyline()[1]
            
        # Get polyline vertices and adjust list if closed
        vertices = list(polyline)
        if polyline.IsClosed:
            del vertices[-1]
            
        # Calculate the angle between each vertex and its neighbours
        for i in range(len(vertices)):
            
            # Get vertex and its neighbours
            if i < len(vertices)-1:
                vtL = vertices[i-1]
                vt = vertices[i]
                vtR = vertices[i+1]
            else:
                vtL = vertices[i-1]
                vt = vertices[i]
                vtR = vertices[0]
                
            # Average the vectors to the two neighbour vertices
            vec1 = (vt - vtL)
            vec2 = vt - vtR
            vec1.Unitize()
            vec2.Unitize()
            vecLvr = -(vec1+vec2)/2
            vecLvr.Unitize()
            
            # Make a circle and a plane through the three vertices
            crc = rc.Geometry.Circle(vtL,vt,vtR)
            pl = rc.Geometry.Plane(vt,vec1,vec2)
            circles.append(crc)
            
            # Rotate the plane to align with the averaged vector
            vecPA = rc.Geometry.Vector3d.VectorAngle(pl.YAxis,vecLvr)
            pl.Rotate(vecPA,pl.ZAxis)
            planes.append(pl)
            
            # Get radius and adjust for large/infinite radii (else Rhino viewport fucks up)
            r = round(crc.Radius,roundDecimal)
            if r < minCircleRadius:
                r = maxCircleRadius
            if r > maxCircleRadius or r == 0:
                r = maxCircleRadius
                crc = None
            radii.append(r)
            
        # Case for open curve (sets end radii/planes to same as neighbour)
        if not polyline.IsClosed:
            
            # Start vertex
            radii[0] = maxCircleRadius
            planes[0].XAxis = planes[1].XAxis
            planes[0].YAxis = planes[1].YAxis
            planes[0].ZAxis = planes[1].ZAxis
            
            # End vertex
            radii[-1] = maxCircleRadius
            planes[-1].XAxis = planes[-2].XAxis
            planes[-1].YAxis = planes[-2].YAxis
            planes[-1].ZAxis = planes[-2].ZAxis
            
        return radii,planes,circles
3

Thank you:)

4

as this topic was the first hit …
just for others that search:
there is also
https://developer.rhino3d.com/api/rhinocommon/rhino.display.displaypipeline/drawcurvaturegraph